tag:theconversation.com,2011:/es/topics/curious-kids-us-74795/articles
Curious Kids US – The Conversation
2024-03-25T12:39:22Z
tag:theconversation.com,2011:article/224152
2024-03-25T12:39:22Z
2024-03-25T12:39:22Z
What is dirt? There’s a whole wriggling world alive in the ground beneath our feet, as a soil scientist explains
<figure><img src="https://images.theconversation.com/files/582688/original/file-20240318-24-77z9su.jpg?ixlib=rb-1.1.0&rect=0%2C9%2C3110%2C2057&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Dig into soil and you'll find rock dust but also thousands of living species.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/little-childs-hands-digging-in-the-mud-royalty-free-image/619539728">ChristinLola/iStock/Getty Images Plus</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>What is dirt? – Belle and Ryatt, ages 7 and 5, Keystone, South Dakota</strong></p>
</blockquote>
<hr>
<p>When you think about dirt, you’re probably picturing soil. There’s so much more going on under our feet than the rock dust, or “dirt,” that gets on your pants.</p>
<p>When <a href="https://arts-sciences.und.edu/academics/biology/brian-darby/index.html">I began studying soil</a>, I was amazed at how much of it is actually alive. Soil is teeming with life, and not just the earthworms that you see on rainy days.</p>
<p>Keeping this vibrant world healthy is <a href="https://www.youtube.com/watch?v=Qas9tPQKd8w">crucial for food, forests and flowers to grow</a> and for the animals that live in the ground to thrive. Here’s a closer look at what’s down there and how it all works together.</p>
<figure class="align-center ">
<img alt="Cupped hands holds soil against a dark background with a tendril of plant root dangling through the fingers." src="https://images.theconversation.com/files/582689/original/file-20240318-20-8yglsj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/582689/original/file-20240318-20-8yglsj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/582689/original/file-20240318-20-8yglsj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/582689/original/file-20240318-20-8yglsj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/582689/original/file-20240318-20-8yglsj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/582689/original/file-20240318-20-8yglsj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/582689/original/file-20240318-20-8yglsj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Soil is a vibrant ecosystem.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/bokeh-photography-of-person-carrying-soil-jin4W1HqgL4">Gabriel Jimenez via Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<h2>The rocky part of soils</h2>
<p>If you scoop up a handful of dry soil, the basic dirt that you feel in your hand is actually very small pieces of <a href="https://passel2.unl.edu/view/lesson/c62dc027ae56/1">weathered rock</a>. These tiny bits eroded from larger rocks over millions of years.</p>
<p>The <a href="https://www.soils4teachers.org/physical-properties/">balance of these particles</a> is important for how well soil can hold water and nutrients that plants need to thrive. </p>
<p>For example, <a href="https://www.masterclass.com/articles/sandy-soil-guide">sandy soil</a> has larger rock grains, so it will be loose and can easily wash away. It won’t hold very much water. <a href="https://www.thespruce.com/understanding-and-improving-clay-soil-2539857">Soil with mostly clay</a> is finer and more compact, making it difficult for plants to access its moisture. In between the two in size is <a href="https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/what-is-silt.htm">silt, a mix of rock dust and minerals</a> often found in fertile flood plains.</p>
<p>Some of the most productive soils have a good balance of sand, clay and silt. <a href="https://www.masterclass.com/articles/how-to-create-loam-soil-for-your-garden">That combination</a>, along with the remnants of plants and animals that have died, helps the soil to retain water, allows plants to access that water and minimizes erosion from wind or rain.</p>
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<img alt="Three tipped over pots spill different types of soil – sandy is heavier grain, clay is finer grain and thicker, and loamy is darker." src="https://images.theconversation.com/files/581414/original/file-20240312-16-meqnvu.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581414/original/file-20240312-16-meqnvu.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581414/original/file-20240312-16-meqnvu.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581414/original/file-20240312-16-meqnvu.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581414/original/file-20240312-16-meqnvu.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=467&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581414/original/file-20240312-16-meqnvu.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=467&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581414/original/file-20240312-16-meqnvu.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=467&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Loamy soil, ideal for gardens, is a mix of sand, clay and silt.</span>
<span class="attribution"><a class="source" href="https://www.nesdis.noaa.gov/learn-about-soil-types">NOAA</a></span>
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<h2>The wriggling, munching parts of soil</h2>
<p>Among all those rock particles is a <a href="https://doi.org/10.3390/app10113717">whole world of living things</a>, each busy doing its job.</p>
<p>To get a sense of just how many creatures are there, picture this: The zoo in Omaha, Nebraska, boasts <a href="https://www.omahazoo.com/">over 1,000 animal species</a>. But if you scooped up a small spoonful of soil in your backyard, it would likely contain <a href="https://www.ceh.ac.uk/our-science/case-studies/case-study-why-do-soil-microbes-matter">at least 10,000 species</a> and around a billion living microscopic cells.</p>
<p>Most of those species are <a href="https://www.westernsydney.edu.au/newscentre/news_centre/story_archive/2018/first_soil_atlas">still largely a mystery</a>. Scientists don’t know much about them or what they do in soil. In fact, most species in soil don’t even have a formal scientific name. But each plays some kind of role in the vast soil ecosystem, including generating the <a href="https://www.aces.edu/blog/topics/farming/essential-plant-elements/">nutrients that plants need to grow</a>.</p>
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<a href="https://images.theconversation.com/files/581410/original/file-20240312-20-vn3j2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two centipede-like creatures caught on camera immediately after a rock is lifted." src="https://images.theconversation.com/files/581410/original/file-20240312-20-vn3j2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581410/original/file-20240312-20-vn3j2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=439&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581410/original/file-20240312-20-vn3j2x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=439&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581410/original/file-20240312-20-vn3j2x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=439&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581410/original/file-20240312-20-vn3j2x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=552&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581410/original/file-20240312-20-vn3j2x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=552&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581410/original/file-20240312-20-vn3j2x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=552&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Lifting a rock reveals a symphylan, or garden centipede, left, and a poduromorph, or plump springtail, munching through the soil.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Symphylan_%26_poduromorph_springtail_(3406419924).jpg">Marshal Hedin via Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>Imagine a leaf falling from a tree in late autumn.</p>
<p>Inside that leaf are a lot of nutrients that plants need, such as nitrogen, potassium and phosphorus. There is also a lot of <a href="https://scied.ucar.edu/learning-zone/earth-system/biogeochemical-cycles">carbon in that leaf</a>, which holds energy that can be used by other organisms such as bacteria and fungi.</p>
<p>The leaf itself is too large for a plant to take up through its roots, of course. But that leaf can be broken down into smaller and smaller pieces. This process of breaking down plant and animal tissue is <a href="https://youtu.be/IBvKKMzXYtY?feature=shared">known as decomposition</a>.</p>
<p>When the leaf first falls to the ground, <a href="https://doi.org/10.3390%2Finsects11010054">arthropods</a> – such as insects, mites and <a href="https://www.chaosofdelight.org/collembola-springtails">collembolans</a> – break the leaf down into smaller chunks by shredding the tissue. Then, an <a href="https://youtu.be/n3wsUYg3XV0?feature=shared">earthworm might come along</a> and eat one of the smaller chunks and break it down even more in <a href="https://www.pbs.org/video/how-do-worms-turn-garbage-into-compost-jwj6cm/">its digestive tract</a>.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/2Pa1FwmKZcQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">PBS explores how earthworms help turn dead plants into fertile soil.</span></figcaption>
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<p>Now the broken-up leaf is small enough for microbes to come in. <a href="https://ohioline.osu.edu/factsheet/anr-36">Bacteria</a> and <a href="https://ohioline.osu.edu/factsheet/anr-37">fungi secrete enzymes</a> into the soil that further break down organic material into even smaller pieces. If enough microbes are active, eventually this organic material will be broken down enough that it can dissolve in water and be taken up by plants that need it.</p>
<p>To aid in this process, there are many small animals, such as <a href="https://www.canr.msu.edu/news/are_soil_nematodes_beneficial_or_harmful">nematodes</a> and <a href="https://www.livingsoil.net/protozoa">amoebae</a>, that consume bacteria and fungi. There are also predatory nematodes that feed on other nematodes to make sure they don’t become too abundant, so everything remains in balance as much as possible. </p>
<p>It’s quite a complicated food web of interacting species in a delicate balance.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/IBvKKMzXYtY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A time-lapse video filmed about 4 inches underground shows a leaf decomposing over 21 days in July. At the end, radish roots make their way down into the soil. Video by Josh Williams.</span></figcaption>
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<p>While some fungi and bacteria <a href="https://www.growingagreenerworld.com/bacteria-fungus-and-viruses-an-overview/">can harm plants</a>, there are many species that are considered beneficial. In fact, they <a href="https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soils/soil-health">may be the key</a> to figuring out how to grow enough crops to feed everyone without degrading and overburdening the soil.</p>
<h2>Figuring out your soil type</h2>
<p>Scientists have named <a href="https://www.nrcs.usda.gov/resources/education-and-teaching-materials/soil-facts">over 20,000 different types</a> of unique soils. If you’re curious about the <a href="https://www.nesdis.noaa.gov/learn-about-soil-types">soil and dirt in your area</a>, the University of California, Davis has a <a href="https://casoilresource.lawr.ucdavis.edu/gmap/">website where you can learn</a> more about local soils and their chemical and physical attributes.</p>
<p><a href="https://www.farmers.gov/conservation/soil-health">Caring for soil</a> to promote its living creatures’ benefits and minimize their harm takes work, but it’s essential for keeping the land healthy and growing food for the future.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/224152/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brian Darby receives funding from the United States Department of Agriculture. </span></em></p>
Rock dust is only part of the story of soil. Living creatures, many of them too tiny to see, keep that soil healthy for growing everything from food to forests.
Brian Darby, Associate Professor of Biology, University of North Dakota
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/222847
2024-03-18T12:30:59Z
2024-03-18T12:30:59Z
How do airplanes fly? An aerospace engineer explains the physics of flight
<figure><img src="https://images.theconversation.com/files/578175/original/file-20240227-28-cejldv.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C7668%2C4449&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">U.S. airlines carry more than 800 million passengers per year.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/airplane-isolated-on-sky-3d-rendering-royalty-free-image/1147868750?phrase=airplanes">Lasha Kilasonia/iStock via Getty Images Plus</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>How do airplanes fly? – Benson, age 10, Rockford, Michigan</strong></p>
</blockquote>
<hr>
<p>Airplane flight is one of the most significant technological achievements of the 20th century. The <a href="https://airandspace.si.edu/explore/stories/wright-brothers">invention of the airplane</a> allows people to travel from one side of the planet to the other in less than a day, compared with weeks of travel by boat and train.</p>
<p>Understanding precisely why airplanes fly is an ongoing challenge for <a href="https://www.clarkson.edu/people/craig-merrett">aerospace engineers, like me</a>, who study and design airplanes, rockets, satellites, helicopters and space capsules. </p>
<p>Our job is to make sure that flying through the air or in space is safe and reliable, by using tools and ideas from science and mathematics, like computer simulations and experiments. </p>
<p>Because of that work, flying in an airplane is <a href="https://usafacts.org/articles/is-flying-safer-than-driving/">the safest way to travel</a> – safer than cars, buses, trains or boats. But although aerospace engineers design aircraft that are stunningly sophisticated, you might be surprised to learn there are still some details about the physics of flight that we don’t fully understand.</p>
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<a href="https://images.theconversation.com/files/577439/original/file-20240222-28-v3tjb4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram of an airplane that shows the four forces of flight." src="https://images.theconversation.com/files/577439/original/file-20240222-28-v3tjb4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/577439/original/file-20240222-28-v3tjb4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=381&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577439/original/file-20240222-28-v3tjb4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=381&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577439/original/file-20240222-28-v3tjb4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=381&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577439/original/file-20240222-28-v3tjb4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=479&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577439/original/file-20240222-28-v3tjb4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=479&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577439/original/file-20240222-28-v3tjb4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=479&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The forces of weight, thrust, drag and lift act on a plane to keep it aloft and moving.</span>
<span class="attribution"><a class="source" href="https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/airplane-cruise-balanced-forces/">NASA</a></span>
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<h2>May the force(s) be with you</h2>
<p>There are <a href="https://www.nasa.gov/stem-content/four-forces-of-flight/#:%7E">four forces</a> that aerospace engineers consider when designing an airplane: weight, thrust, drag and lift. Engineers use these forces to help design the shape of the airplane, the size of the wings, and figure out how many passengers the airplane can carry. </p>
<p>For example, when an airplane takes off, the thrust must be greater than the drag, and the lift must be greater than the weight. If you watch an airplane take off, you’ll see the wings change shape using flaps from the back of the wings. The flaps help make more lift, but they also make more drag, so a powerful engine is necessary to create more thrust. </p>
<p>When the airplane is high enough and is cruising to your destination, lift needs to balance the weight, and the thrust needs to balance the drag. So the pilot pulls the flaps in and can set the engine to produce less power.</p>
<p>That said, let’s define what force means. According to <a href="https://ca.pbslearningmedia.org/resource/4079abf0-7a4b-4f49-80ad-c69cd06a80f9/newtons-second-law-of-motion/">Newton’s Second Law</a>, a force is a mass multiplied by an acceleration, or F = ma. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/579678/original/file-20240304-22-jrh9mr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A black and white historical photograph of the first flight of the Wright brothers." src="https://images.theconversation.com/files/579678/original/file-20240304-22-jrh9mr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/579678/original/file-20240304-22-jrh9mr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=381&fit=crop&dpr=1 600w, https://images.theconversation.com/files/579678/original/file-20240304-22-jrh9mr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=381&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/579678/original/file-20240304-22-jrh9mr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=381&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/579678/original/file-20240304-22-jrh9mr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=479&fit=crop&dpr=1 754w, https://images.theconversation.com/files/579678/original/file-20240304-22-jrh9mr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=479&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/579678/original/file-20240304-22-jrh9mr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=479&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">On Dec. 17, 1903, the Wright brothers made their first flight at Kitty Hawk, N.C. Orville Wright is at the controls, while Wilbur looks on.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-flyer-takes-off-from-kill-devil-hill-with-orville-news-photo/517389284?adppopup=true">Bettmann via Getty Images</a></span>
</figcaption>
</figure>
<p>A force that everyone encounters every day is <a href="https://spaceplace.nasa.gov/what-is-gravity/en/#:%7E">the force of gravity</a>, which keeps us on the ground. When you get weighed at the doctor’s office, they’re actually measuring the amount of force that your body applies to the scale. When your weight is given in pounds, that is a measure of force. </p>
<p>While an airplane is flying, gravity is pulling the airplane down. That force is the weight of the airplane. </p>
<p>But its engines push the airplane forward because they create <a href="https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/what-is-thrust/">a force called thrust</a>. The engines pull in air, which has mass, and quickly push that air out of the back of the engine – so there’s a mass multiplied by an acceleration. </p>
<p>According to <a href="https://www.youtube.com/watch?v=a-wh3fJRdjo">Newton’s Third Law</a>, for every action there’s an equal and opposite reaction. When the air rushes out the back of the engines, there is a reaction force that pushes the airplane forward – that’s called thrust.</p>
<p>As the airplane flies through the air, the shape of the airplane pushes air out of the way. Again, by Newton’s Third Law, this air pushes back, <a href="https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/what-is-drag/#:%7E">which leads to drag</a>. </p>
<p>You can experience something similar to drag when swimming. Paddle through a pool, and your arms and feet provide thrust. Stop paddling, and you will keep moving forward because you have mass, but you will slow down. The reason that you slow down is that the water is pushing back on you – that’s drag. </p>
<h2>Understanding lift</h2>
<p><a href="https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/what-is-lift/">Lift</a> is more complicated than the other forces of weight, thrust and drag. It’s created by the wings of an airplane, and the shape of the wing is critical; that shape is <a href="https://howthingsfly.si.edu/media/airfoil#:%7E">known as an airfoil</a>. Basically it means the top and bottom of the wing are curved, although the shapes of the curves can be different from each other. </p>
<p>As air flows around the airfoil, <a href="https://www.youtube.com/watch?v=UO75jDwGCdQ">it creates pressure</a> – a force spread out over a large area. Lower pressure is created on the top of the airfoil compared to the pressure on the bottom. Or to look at it another way, air travels faster over the top of the airfoil than beneath. </p>
<p>Understanding why the pressure and speeds are different on the top and the bottom is <a href="https://airandspace.si.edu/multimedia-gallery/lift-and-copjpg">critical to understand lift</a>. By improving our understanding of lift, engineers can design more fuel-efficient airplanes and give passengers more comfortable flights.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/579698/original/file-20240304-24-6df49v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram that shows how the airfoil of a plane works." src="https://images.theconversation.com/files/579698/original/file-20240304-24-6df49v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/579698/original/file-20240304-24-6df49v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=385&fit=crop&dpr=1 600w, https://images.theconversation.com/files/579698/original/file-20240304-24-6df49v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=385&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/579698/original/file-20240304-24-6df49v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=385&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/579698/original/file-20240304-24-6df49v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=484&fit=crop&dpr=1 754w, https://images.theconversation.com/files/579698/original/file-20240304-24-6df49v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=484&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/579698/original/file-20240304-24-6df49v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=484&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Note the airfoil, which is a specific wing shape that helps keep a plane in the air.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/how-airplanes-fly-royalty-free-illustration/1401215523?phrase=airfoil+diagram&adppopup=true">Dimitrios Karamitros/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<h2>The conundrum</h2>
<p>The reason why air moves at different speeds around an airfoil remains mysterious, and <a href="https://www.scientificamerican.com/video/no-one-can-explain-why-planes-stay-in-the-air/">scientists are still investigating</a> this question. </p>
<p>Aerospace engineers have measured these pressures on a wing in both wind tunnel experiments and during flight. We can create models of different wings to predict if they will fly well. We can also change lift by changing a wing’s shape to create airplanes that fly for long distances or fly very fast. </p>
<p>Even though we still don’t fully know why lift happens, aerospace engineers work with mathematical equations that recreate the different speeds on the top and bottom of the airfoil. Those equations describe a process <a href="https://howthingsfly.si.edu/media/circulation-theory-lift">known as circulation</a>. </p>
<p>Circulation provides aerospace engineers with a way to model what happens around a wing even if we do not completely understand why it happens. In other words, through the use of math and science, we are able to build airplanes that are safe and efficient, even if we don’t completely understand the process behind why it works.</p>
<p>Ultimately, if aerospace engineers can figure out why the air flows at different speeds depending on which side of the wing it’s on, we can design airplanes that use less fuel and pollute less.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/222847/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Craig Merrett receives funding from the Office of Naval Research and L3Harris. He is affiliated with the American Institute for Aeronautics and Astronautics, and is a licensed professional engineering in Ontario, Canada. Dr. Merrett is an associate professor in the Department of Mechanical and Aerospace Engineering at Clarkson University, Potsdam, NY. </span></em></p>
People have been flying airplanes for well over a century. Engineers know how to balance all the forces at play, but still aren’t exactly sure how some of the physics of flight actually works.
Craig Merrett, Professor of Mechanical and Aerospace Engineering, Clarkson University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/213208
2024-03-04T13:35:40Z
2024-03-04T13:35:40Z
Why do bees have queens? 2 biologists explain this insect’s social structure – and why some bees don’t have a queen at all
<figure><img src="https://images.theconversation.com/files/578405/original/file-20240227-30-jjne39.jpg?ixlib=rb-1.1.0&rect=9%2C0%2C3019%2C1971&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The queen, on the right with a larger, darker body, is bigger than the worker bees in the colony and lives several times longer.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/bees-from-a-bee-colony-with-a-queen-are-seen-on-a-honeycomb-news-photo/1233050929">Jens Kalaene/picture alliance via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why do bees have queens? – Rhylie, age 8, Rosburg, Washington</strong></p>
</blockquote>
<hr>
<p>When you think “bee,” you likely picture one species that lives all over the world: the <a href="https://www.natgeokids.com/au/discover/animals/insects/honey-bees/">honey bee</a>. And honey bees have queens, a female who lays essentially all of the eggs for the colony.</p>
<p>But most bees don’t have queens. With about <a href="https://www.usgs.gov/faqs/how-many-species-native-bees-are-united-states#:%7E">20,000 species of bees worldwide</a> – that’s about 2 trillion bees – the majority of them don’t even live in groups. They do just fine <a href="https://tpwd.texas.gov/huntwild/wild/wildlife_diversity/nongame/native-pollinators/solitary-social.phtml#:%7E">without queens or colonies</a>. </p>
<p>Instead, a single female lays eggs in a simple nest, either inside a plant stem or an underground tunnel. She provides each egg with a ball of pollen mixed with nectar that she collected from flowers, and she leaves the eggs to hatch and develop on their own. She doesn’t have anyone to help with this process. </p>
<p>These bee species, often spectacularly beautiful, are <a href="https://www.fs.usda.gov/wildflowers/pollinators/animals/bees.shtml">important pollinators of many crops and plants</a>, though most people aren’t even aware of them. </p>
<p>Since lots of bees successfully live without a queen, what is it that queens provide for the bee species that do have them? <a href="https://scholar.google.com/citations?user=KF4sBDIAAAAJ&hl=en&oi=ao">We are behavioral ecologists</a> <a href="https://scholar.google.com/citations?user=r9Wuv18AAAAJ&hl=en&oi=ao">who study social insects</a>, and this question is at the heart of our research. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/578406/original/file-20240227-26-jefrkz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="handful of bees flying toward a busy hive" src="https://images.theconversation.com/files/578406/original/file-20240227-26-jefrkz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/578406/original/file-20240227-26-jefrkz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/578406/original/file-20240227-26-jefrkz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/578406/original/file-20240227-26-jefrkz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/578406/original/file-20240227-26-jefrkz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/578406/original/file-20240227-26-jefrkz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/578406/original/file-20240227-26-jefrkz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A bee colony may have many thousands of workers who support the single queen.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/bees-flying-royalty-free-image/172457089">bo1982/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<h2>A queen, workers and drones</h2>
<p>Along with honey bees, two other kinds of bees also have queens: <a href="https://www.treehugger.com/bumblebee-facts-5119379">bumble bees</a>, which are found on all continents except Australia and Antarctica, and <a href="https://beeswiki.com/stingless-bees/">stingless bees</a>, which are found primarily in tropical areas. </p>
<p>One honey bee colony – also called a hive – may have <a href="https://www.buzzaboutbees.net/honey-bee-facts.html">more than 50,000 bees</a>, while bumble bee colonies usually have just a few hundred bees. Stingless bee colonies are often small, but some are as large as the biggest honey bee hives. </p>
<p>These bees’ social structures have two more things in common besides the egg-laying queen: the female workers who care for the colony, and the males, <a href="https://www.buzzaboutbees.net/dronebee.html">sometimes called “drones</a>.” </p>
<p>Notice the males are not included in the “worker” group. Males generally don’t help collect nectar or pollen, protect and maintain the hive, or care for the young larvae. The females do all of those jobs. </p>
<p>Instead, the males have one task: to find and then mate with a female who may become a future queen. After building their strength, males leave the hive to join thousands of other drones to wait for new queens that are also looking for mates. If males are lucky enough to mate, they die soon afterward. In contrast, females typically mate with many different males before starting their lives as egg-laying queens. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/9ePic3dtykk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Female worker bees do pretty much all the work.</span></figcaption>
</figure>
<h2>The isolated queen</h2>
<p>Maybe you imagine a queen as the one in charge, ordering everyone around. But that’s a case of language being misleading. Unlike human queens who lead their people, bee queens don’t rule over their workers. </p>
<p>Instead, particularly for honey bees, the queen is rather isolated from what’s happening in the hive. Remember, she just lays eggs, up to 2,000 in a day. The workers surround and take care of her while managing the colony. The queen bee might <a href="https://www.buzzaboutbees.net/how-long-do-bees-live.html">live for a few years</a>, much longer than female worker bees and drones.</p>
<p>Other animals also live in social groups with a division of labor between those who reproduce and those who maintain the colony. <a href="https://www.natgeokids.com/uk/discover/animals/insects/ant-facts/">Ants</a>, <a href="https://kids.britannica.com/kids/article/termite/353849#:%7E">termites</a> and <a href="https://kids.britannica.com/kids/article/wasp/353914#:%7E">some wasps</a> – like yellow jackets and hornets – have a similar kind of colony structure. So does the <a href="https://nationalzoo.si.edu/animals/naked-mole-rat">naked mole rat</a>. Why did these groups evolve to have queens? </p>
<h2>Family ties</h2>
<p>One way for an organism to pass on genes is by having offspring. </p>
<p>Another way is to help close relatives, who are likely to share many of your same genes, to produce more offspring than they would if they were on their own. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/578408/original/file-20240227-28-3bsd6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="dozens of hexagonal cells, each containing a tiny white egg or slightly larger white worm" src="https://images.theconversation.com/files/578408/original/file-20240227-28-3bsd6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/578408/original/file-20240227-28-3bsd6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/578408/original/file-20240227-28-3bsd6f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/578408/original/file-20240227-28-3bsd6f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/578408/original/file-20240227-28-3bsd6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/578408/original/file-20240227-28-3bsd6f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/578408/original/file-20240227-28-3bsd6f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Honey bee eggs and larvae develop one to a cell.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/honey-bee-eggs-and-larva-in-comb-with-black-royalty-free-image/1455295651">Megan Kobe/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<p>This option is pretty much what happens in a bee colony. Those thousands of female worker bees may not themselves reproduce, but the queen is their mother. They help her produce another generation of siblings who will one day be their sisters. In this way, the female worker bees are passing their genes on to the next generation, just not directly. </p>
<p>Something else to consider: A honey bee hive is a <a href="https://www.beebasket.in/stories/nature/hive-architecture-the-engineering-marvel-of-beehives/#:%7E">wonderfully complex structure</a>. The layers of wax combs built to store honey and raise offspring are a marvel of architecture and require a large workforce for construction, ongoing repairs and protection from intruders or predators. </p>
<p>So you might ask: Which came first? Social groups with queens and workers producing large numbers of related offspring that required more elaborate nest structures? Or did the complex nest arise first, which led to greater success for groups that evolved to divide tasks among queens and workers? </p>
<p>These are fascinating questions that biologists have been exploring for decades. But both of these factors – the division of labor and the complex hive structures – help explain why there are bees with queens. </p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/213208/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
A queen’s main job in the hive is to lay eggs and pass genes on to offspring. But many bee species do just fine without queens or big colonies.
Phil Starks, Associate Professor of Biology, Tufts University
Aviva Liebert, Professor of Biology, Framingham State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/222851
2024-02-26T13:38:23Z
2024-02-26T13:38:23Z
How is snow made? An atmospheric scientist describes the journey of frozen ice crystals from clouds to the ground
<figure><img src="https://images.theconversation.com/files/576863/original/file-20240220-22-v6kq2o.jpg?ixlib=rb-1.1.0&rect=22%2C5%2C3764%2C2055&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Some parts of the U.S. see well over 100 inches (2.5 meters) of snow per year.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/downhill-sledging-royalty-free-image/488074477?phrase=sledding+in+snow">Edoardo Frola/Moment Open via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>How is snow made? – Tenley, age 7, Rockford, Michigan</strong></p>
</blockquote>
<hr>
<p>The thought of snow can conjure up images of powdery slopes, days out of school or hours of shoveling. For millions of people, it’s an inevitable part of life – but you may rarely stop to think about what made the snow.</p>
<p>As a <a href="https://www.eaps.purdue.edu/people/profile/ablanch.html">professor of atmospheric and planetary sciences</a>, <a href="https://scholar.google.com/citations?user=xClwTzUAAAAJ&hl=en&oi=ao">I’ve studied how ice crystals floating</a> in the sky become the snow that coats the ground.</p>
<p>It all starts in the clouds.</p>
<p>Clouds form when air near the Earth’s surface rises. This happens when sunlight warms the ground and the air closest to it, just like the Sun can warm your face on a cold winter day. </p>
<p>As the slightly warmer air rises, it cools – and the water vapor in that rising air condenses to form liquid water or water ice. From that, <a href="https://climatekids.nasa.gov/cloud-formation/#:%7E">a cloud is born</a>. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/Cf6El0mI1fM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">You need just two things for snow to form.</span></figcaption>
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<h2>Endless pathways</h2>
<p>When temperatures are well below freezing on the ground, the clouds are primarily made of water in the form of ice. Under 32 degrees Fahrenheit – that’s zero degrees Celsius – the frozen water molecules arrange themselves into a hexagonal, or six-sided, crystalline shape. As ice crystals grow and clump together, they become too heavy to stay aloft. With the help of gravity, they begin to fall back down through and eventually out of the cloud.</p>
<p>What these ice crystals look like once they reach land depends on the temperature and humidity of the atmosphere. As the humidity – or the amount of water vapor in the cloud – increases, some of the ice crystals will grow intricate arms at their six corners. That branching process creates what we think of as the <a href="https://www.timeforkids.com/g2/snowflake-science-g2-5-plus/?rl=en-500">characteristic shapes of snowflakes</a>. </p>
<p>No two ice crystals take the same path through a cloud. Instead, every ice crystal experiences different temperatures and humidities as it travels through the cloud, whether going up or down. The ever-changing conditions, combined with the infinite number of paths the crystals could take, result in a unique growth history and crystalline shape for each and every snowflake. This is why you’ve likely heard the saying, “<a href="https://www.willyswilderness.org/post/no-two-snowflakes-are-alike-it-s-actually-true">No two snowflakes are exactly alike</a>.” </p>
<p>Many times, these differences are visible to the naked eye; sometimes a microscope is required to tell them apart. Either way, scientists who study clouds and snow can examine a snowflake and ultimately understand the path it took through the cloud to land on your hand. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Snow crystals attached to a window." src="https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=636&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=636&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=636&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=799&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=799&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=799&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">It takes approximately one hour for a snowflake to reach the ground.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/snowflakes-royalty-free-image/158720307?phrase=snowflakes">LiLi/iStock via Getty Images Plus</a></span>
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<h2>Liquid water as glue</h2>
<p>When snow falls from the sky, you don’t usually see individual ice crystals, but rather clumps of <a href="https://scied.ucar.edu/learning-zone/storms/snowflakes">crystals stuck together</a>. One way ice crystals aggregate is through what’s called mechanical interlocking. When ice crystals bump into each other, crystals with intricate branches and arms intertwine and stick to others. </p>
<p>This mechanism is the main sticking process in cooler, drier conditions – what people call a “<a href="https://compuweather.com/the-important-difference-between-wet-snow-and-dry-snow/">dry snow</a>.” The result is a snow perfect for skiing, and easily picked up by the wind, but that won’t hold together when formed into a snowball. </p>
<p>The second way to stick ice crystals together is to warm them up a bit. When ice crystals fall through a region of cloud or atmosphere where the temperature is slightly above freezing, the edges of the crystals start to melt. Just a tiny bit of liquid water allows ice crystals that bump into each other to stick together very efficiently, almost like glue. </p>
<p>The result? Large clumps of ice crystals falling from the sky, what we call a “<a href="https://www.acurite.com/blog/types-of-snow.html">wet snow</a>” – less than ideal for hitting the slopes but perfect for building a snowman. </p>
<p>Snow formed in clouds typically reaches the ground only in winter. But almost all clouds, no matter the time of year or location, <a href="https://scijinks.gov/clouds/">contain some ice</a>. This is true even for clouds in warm tropical regions, because the atmosphere above us is much colder and can reach temperatures below freezing even on the warmest of days. In fact, scientists who study weather discovered that clouds containing ice produce more rain than those that don’t contain any ice at all.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/222851/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alexandria Johnson receives funding from NASA. </span></em></p>
There are an infinite number of paths an ice crystal can take before you touch it.
Alexandria Johnson, Professor of Atmospheric and Planetary Sciences, Purdue University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/218330
2024-02-19T13:36:56Z
2024-02-19T13:36:56Z
Why does a leap year have 366 days?
<figure><img src="https://images.theconversation.com/files/575717/original/file-20240214-24-h6q6if.jpg?ixlib=rb-1.1.0&rect=38%2C23%2C5137%2C3422&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Leap Day is coming.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/calendar-on-february-29-on-a-leap-year-leap-day-royalty-free-image/1196849410">Marvin Samuel Tolentino Pineda/iStock, via Getty images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p>Why does a leap year have 366 days? Does the Earth move slower every four years? – Aarush, age 8, Milpitas, California</p>
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<hr>
<p>You may be used to hearing that it takes the Earth 365 days to make a full lap, but that journey actually lasts about 365 and a quarter days. Leap years help to keep the 12-month calendar matched up with Earth’s movement around the Sun. </p>
<p>After four years, those leftover hours add up to a whole day. In a leap year, we add this extra day to the month of February, making it 29 days long instead of the usual 28.</p>
<p>The idea of an annual catch-up dates back to ancient Rome, where people had a calendar with 355 days instead of 365 because it was based on cycles and phases of the Moon. They noticed that their calendar was getting out of sync with the seasons, so they began adding an extra month, <a href="https://www.britannica.com/science/Roman-republican-calendar">which they called Mercedonius</a>, every two years to catch up with the missing days.</p>
<p>In the year 45 B.C.E., Roman emperor Julius Caesar introduced a solar calendar, based on one developed in Egypt. Every four years, February received an extra day to keep the calendar in line with the Earth’s journey around the Sun. In honor of Caesar, this system is still known as the Julian calendar.</p>
<p>But that wasn’t the last tweak. As time went on, people realized that the Earth’s journey wasn’t exactly 365.25 days – it <a href="https://airandspace.si.edu/stories/editorial/science-leap-year">actually took 365.24219 days</a>, which is about 11 minutes less. So adding a whole day every four years was actually a little more correction than was needed. </p>
<p>In 1582, Pope Gregory XIII signed an order that made a small adjustment. There would still be a leap year every four years, except in “century” years – years divisible by 100, like 1700 or 2100 – unless they were also divisible by 400. It might sound a bit like a puzzle, but this adjustment made the calendar <a href="https://airandspace.si.edu/stories/editorial/science-leap-year">even more accurate</a> – and from that point on, it was known as the Gregorian calendar.</p>
<h2>What if we didn’t have leap years?</h2>
<p>If the calendar didn’t make that small correction every four years, it would gradually fall out of alignment with the seasons. Over centuries, this could lead to the <a href="https://www.britannica.com/story/whats-the-difference-between-a-solstice-and-an-equinox">solstices and equinoxes</a> occurring at different times than expected. Winter weather might develop in what the calendar showed as summer, and farmers could become confused about when to plant their seeds.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/YTOr8_ILqGw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Without leap years, our calendar would gradually become disconnected from the seasons.</span></figcaption>
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<p>Other calendars around the world have their own ways of keeping time. The Jewish calendar, which is regulated by <a href="https://www.britannica.com/topic/Jewish-religious-year">both the Moon and the Sun</a>, is like a big puzzle with a 19-year cycle. Every now and then, it adds a leap month to make sure that special celebrations happen at just the right time. </p>
<p>The <a href="https://ing.org/resources/for-all-groups/calendar-of-important-islamic-dates/">Islamic calendar</a> is even more unusual. It follows the <a href="https://spaceplace.nasa.gov/moon-phases/en/">phases of the Moon</a> and doesn’t add extra days. Since a lunar year is only about 355 days long, key dates on the Islamic calendar move 10 to 11 days earlier each year on the solar calendar. </p>
<p>For example, Ramadan, the <a href="https://ing.org/resources/for-all-groups/calendar-of-important-islamic-dates/">Islamic month of fasting</a>, falls in the ninth month of the Islamic calendar. In 2024, it will run from March 11 to April 9; in 2025, it will occur from March 1-29; and in 2026, it will be celebrated from Feb. 18 to March 19.</p>
<h2>Learning from the planets</h2>
<p>Astronomy originated as a way to make sense of our daily lives, linking the events around us to celestial phenomena. The concept of leap years exemplifies how, from early ages, humans found order in conditions that seemed chaotic. </p>
<p>Simple, unsophisticated but effective tools, born from creative ideas of ancient astronomers and visionaries, provided the first glimpses into understanding the nature that envelops us. Some <a href="https://www.britannica.com/science/astronomy/History-of-astronomy">ancient methods</a>, such as <a href="https://sci.esa.int/web/gaia/-/53196-the-oldest-sky-maps">astrometry and lists of astronomical objects</a>, persist even today, revealing the timeless essence of our quest to understand nature. </p>
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<a href="https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Photograph of an intricate schematic guide to the night sky." src="https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=356&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=356&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=356&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=447&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=447&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=447&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Ancient Egyptians were dedicated astronomers. This section from the ceiling of the tomb of Senenmut, a high court official in Egypt, was drawn sometime circa 1479–1458 B.C.E. It shows constellations, protective gods and 24 segmented wheels for the hours of the day and the months of the year.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Senenmut-Grab.JPG">NebMaatRa/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>People who do research in physics and astronomy, the <a href="https://scholar.google.com/citations?user=t4L_D18AAAAJ&hl=en">field that I study</a>, are inherently curious about the workings of the universe and our origins. This work is exciting, and also extremely humbling; it constantly shows that in the grand scheme, our lives occupy a mere second in the vast expanse of space and time – even in leap years when we add that extra day.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/218330/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bhagya Subrayan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Humans have synced their calendars to the sun and moon for centuries, but every so often, these systems need a little correction.
Bhagya Subrayan, PhD Student in Physics and Astronomy, Purdue University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/221677
2024-02-12T13:24:56Z
2024-02-12T13:24:56Z
Can anyone make a citizen’s arrest? The history and legalities of catching criminals yourself
<figure><img src="https://images.theconversation.com/files/574490/original/file-20240208-28-q5mmu6.jpg?ixlib=rb-1.1.0&rect=0%2C6%2C4600%2C2452&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Can you detain someone you just saw break the law?</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/man-mugging-woman-in-street-royalty-free-image/BC3542-001">Alan Thornton/The Image Bank via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Can anyone make a citizen’s arrest, even me? – Henry, age 12, Winter Hill, Massachusetts</strong></p>
</blockquote>
<hr>
<p>What does Spider-Man do when he sees someone commit a crime and there are no police officers around to help? He swings in, wraps the wrongdoer in his web and leaves them hanging from a telephone pole until the cops take over. </p>
<p>But is he allowed to do that? Are you?</p>
<h2>Seizing criminals</h2>
<p>Until about 200 years ago, uniformed police officers and police departments as we know them today <a href="https://time.com/4779112/police-history-origins/">didn’t exist in the United States</a>. It was up to the citizens to arrest criminals.</p>
<p>In 1285, England introduced what we now know as “citizen’s arrests” in a law called <a href="https://study.sagepub.com/rowe3e/student-resources/chapter-3/the-statute-of-winchester">the Statute of Winchester</a>. It allowed any person to arrest – in other words, capture – lawbreakers. This concept spread throughout the English colonies, which ultimately became their own countries, including Australia, Canada and the United States. Other <a href="https://en.wikipedia.org/wiki/Citizen%27s_arrest">countries have adopted similar rules</a>.</p>
<p>In the United States, citizen’s arrests have a pretty dark history. Originally, <a href="https://www.fastcompany.com/90528764/the-troubling-history-of-citizens-arrests-from-slave-patrols-to-ahmaud-arbery-to-ice">only white men could make citizen’s arrests</a>. By the mid-1600s, many militias and city watchmen, especially in the South, used that power to <a href="https://www.fastcompany.com/90528764/the-troubling-history-of-citizens-arrests-from-slave-patrols-to-ahmaud-arbery-to-ice">intimidate and terrorize enslaved and free Black communities</a>.</p>
<p>This practice continued <a href="https://racism.org/articles/law-and-justice/criminal-justice-and-racism/134-police-brutality-and-lynchings/9617-a-legacy">through the Civil War</a>, <a href="https://historynewsnetwork.org/article/175619">the Jim Crow era and even into the 1900s</a>, with vigilantes – people who appoint themselves to catch and punish others – engaging in heinous abuses, <a href="https://theconversation.com/lynching-memorial-shows-women-were-victims-too-95029">including lynchings</a>. Just recently, in 2020, Ahmaud Arbery, a Black man who was jogging around his Georgia neighborhood, <a href="https://theconversation.com/jury-finds-3-georgia-men-guilty-of-ahmaud-arbery-murder-3-essential-reads-172493">was shot and killed</a> by a group of white men who accosted him because they wrongly thought he had committed a crime.</p>
<p>Despite this history, most states still have citizen’s arrest <a href="https://www.washingtonpost.com/nation/2021/11/05/ahmaud-arbery-citizens-arrest-vigilante/">laws on the books</a>.</p>
<h2>Making a legal citizen’s arrest</h2>
<p>Arrest literally means “to stop.” If someone wants to leave, you usually can’t stop them – that could be considered false imprisonment or even kidnapping. Citizen’s arrest laws are an exception to that general rule; they allow everyday people to make an arrest.</p>
<p>When the police make an arrest, they typically handcuff the subject and take them in a secure transport vehicle to a booking facility, such as the county jail. When Spidey webs a wrongdoer, he can’t just take them back to Aunt May’s apartment. Making a citizen’s arrest means holding the lawbreaker in place until the police arrive and take over.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/574491/original/file-20240208-24-qtcx1d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A blurry, dark black-and-white picture of a figure holding what could be a knife, or something else entirely" src="https://images.theconversation.com/files/574491/original/file-20240208-24-qtcx1d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/574491/original/file-20240208-24-qtcx1d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/574491/original/file-20240208-24-qtcx1d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/574491/original/file-20240208-24-qtcx1d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/574491/original/file-20240208-24-qtcx1d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/574491/original/file-20240208-24-qtcx1d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/574491/original/file-20240208-24-qtcx1d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">You’d better be sure about what you think you saw.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/man-holding-knife-in-kitchen-rear-view-silhouette-royalty-free-image/588312130">Glasshouse Images/The Image Bank via Getty Images</a></span>
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<p>When can someone make a citizen’s arrest? The rules are a bit different in every state, which can make things confusing. You can ask a librarian to help you find information about the law in your state, but here are some common requirements to get you started:</p>
<p><strong>Who can make a citizen’s arrest?</strong> Although some state laws use the word “<a href="https://www.scstatehouse.gov/code/t17c013.php">citizen</a>,” most states allow any “<a href="https://statutes.capitol.texas.gov/Docs/CR/htm/CR.14.htm">person</a>” or any “<a href="https://www.revisor.mn.gov/statutes/cite/629.37">private person</a>” – as opposed to a public employee such as a police officer – to make a citizen’s arrest. Despite the name, you usually don’t have to be a citizen. And most states don’t require any minimum age, so it looks like high school student Peter Parker, Spider-Man’s alter ego, is good to go.</p>
<p><strong>Did you see it, and how serious is it?</strong> Most states allow you to make a citizen’s arrest for a minor crime – those <a href="https://www.britannica.com/topic/crime-law/Classification-of-crimes">categorized as a misdemeanor</a> – only if you actually saw the person commit the crime. Some states allow a citizen’s arrest for a minor crime only if it is considered a “breach of peace,” meaning the crime is likely to disturb other people, such as fighting in public. For felonies, a more serious category of crime, the law usually allows you to make a citizen’s arrest even if you didn’t see the person commit the crime.</p>
<p><strong>You’d better be sure!</strong> In most states, citizen’s arrest laws apply only if the person actually committed a crime. If you make a mistake by making a citizen’s arrest of someone who didn’t actually commit a crime, the <a href="https://www.findlaw.com/injury/torts-and-personal-injuries/false-imprisonment.html">person you arrested can sue you</a>. You might even get <a href="https://www.law.cornell.edu/wex/false_imprisonment">arrested</a> yourself!</p>
<p>This is different from when police arrest someone. Law enforcement officers need “<a href="https://www.law.cornell.edu/wex/probable_cause">probable cause</a>,” which is the legal standard for how sure you need to be that a person committed a crime before arresting them. As long as an officer meets the probable cause standard, they won’t get in trouble, even if they’re ultimately mistaken about the person committing a crime.</p>
<p><strong>Try not to rough anyone up.</strong> Someone making a citizen’s arrest is usually allowed to use a reasonable amount of physical force to ensure that the lawbreaker stops committing the crime and can’t leave. But that doesn’t mean you can do anything you want. The type and amount of force you use must be <a href="https://nyupress.org/9781479814657/evaluating-police-uses-of-force/">closely related</a> to whether the other person is trying to get away and, if so, what they’re doing.</p>
<p><strong>Just because you can doesn’t mean you should.</strong> Making a citizen’s arrest is no joke. There’s the danger of making a mistake about what the person did and whether it was a crime. After all, most people don’t know exactly what the law allows or prohibits, so it’s easy to get something wrong.</p>
<p>And there’s the danger of getting hurt. Most people aren’t trained or equipped to arrest someone safely, and they rarely have backup available like the police do. If you see a crime occur, it’s better to call the police and be a good witness than it is to try to make a citizen’s arrest yourself. </p>
<p>So, what do you think: Is Spider-Man allowed to make a citizen’s arrest? And if he is, does that make him a hero or a vigilante?</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/221677/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Stopping someone against their will can be false imprisonment or even kidnapping. There are laws that determine who is acting as a hero and who is acting as a vigilante.
Seth W. Stoughton, Professor of Law, University of South Carolina
Caroline McAtee, Law Student at the University of South Carolina School of Law, Research Assistant for the Excellence in Policing and Public Safety Program, University of South Carolina
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/219169
2024-02-05T13:30:00Z
2024-02-05T13:30:00Z
Why do people and animals need to breathe? A biologist explains why you need a constant source of oxygen
<figure><img src="https://images.theconversation.com/files/567973/original/file-20240104-26-jrvms0.jpg?ixlib=rb-1.1.0&rect=419%2C364%2C3255%2C2085&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Your blood's natural limit to how much oxygen it can hold means you can't stockpile it.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/girl-swimming-in-idyllic-caribbean-sea-take-a-royalty-free-image/1394071551">Lisa520/E+ via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why do humans and animals have to breathe? – Tennessee, age 7, Hartford, Kentucky</strong></p>
</blockquote>
<hr>
<p>You need to breathe for the same reason you need to eat: It helps you make the energy your body requires. </p>
<p>You probably already know that food is fuel for your body. When you eat, food gets broken down in your stomach and <a href="https://www.vattenhallen.lu.se/english/experiences/from-mouth-to-rectum/">enters your bloodstream</a>.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/568258/original/file-20240108-16-q7f3ve.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A plastic object on a stand that is tube shaped with part of it cut off showing an interior space with fuzzy looking walls with dividers." src="https://images.theconversation.com/files/568258/original/file-20240108-16-q7f3ve.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/568258/original/file-20240108-16-q7f3ve.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=801&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568258/original/file-20240108-16-q7f3ve.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=801&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568258/original/file-20240108-16-q7f3ve.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=801&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568258/original/file-20240108-16-q7f3ve.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1006&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568258/original/file-20240108-16-q7f3ve.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1006&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568258/original/file-20240108-16-q7f3ve.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1006&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A plastic model of a mitochondrion.</span>
<span class="attribution"><a class="source" href="https://coimages.sciencemuseumgroup.org.uk/images/24/460/large_2010_0084__0001_.jpg">Science Museum Group Collection © The Board of Trustees of the Science Museum</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<p>From there, it gets delivered to your cells. Inside your cells are even <a href="https://collection.sciencemuseumgroup.org.uk/objects/co505977/plastic-organelle-model-of-a-mitochondrion-from-a-cell-model-representation">tinier structures called mitochondria</a>, which are the engines that power your entire body. Your mitochondria use the nutrients from food as fuel. But to turn it into energy, they need one more ingredient – oxygen.</p>
<p><a href="https://scholar.google.com/citations?hl=en&user=tuuK7xcAAAAJ">I am a biologist who studies</a> animals and plants. All living things need oxygen, except for <a href="https://en.wikipedia.org/wiki/Obligate_anaerobe">some bacteria</a> and <a href="https://www.doi.org/10.1186/1741-7007-8-30">a few tiny animals</a> that don’t. You might be surprised to learn how many ways there are to get oxygen – breathing is only one of them.</p>
<h2>Lungs and their linings</h2>
<p>When you breathe in, your lungs temporarily trap oxygen, allowing it to pass through very <a href="https://www.britannica.com/science/pulmonary-alveolus">thin surfaces in your lungs</a> into your bloodstream. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/567972/original/file-20240104-19-n4vt7u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A central tube comes down, which then branches and rebranches over and over." src="https://images.theconversation.com/files/567972/original/file-20240104-19-n4vt7u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/567972/original/file-20240104-19-n4vt7u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=603&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567972/original/file-20240104-19-n4vt7u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=603&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567972/original/file-20240104-19-n4vt7u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=603&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567972/original/file-20240104-19-n4vt7u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=758&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567972/original/file-20240104-19-n4vt7u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=758&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567972/original/file-20240104-19-n4vt7u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=758&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A CT scan of healthy lungs.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/healthy-lungs-ct-scan-royalty-free-image/1786377109">RAJAAISYA/Science Photo Library via Getty Images</a></span>
</figcaption>
</figure>
<p>Because you need a lot of oxygen, your lungs need a lot of surface area to do their job. They achieve this by having millions of <a href="https://upload.wikimedia.org/wikipedia/commons/b/bb/Lung_structure_normal.jpg">little air sacs</a> lined with tiny blood vessels called capillaries.</p>
<p>If you could somehow flatten out all the capillary surface area in your lungs, it would more than cover the floor of <a href="https://seatingchartmaker.app/articles/average-classroom-size-square-feet/#classroom-size-by-us-state">an average classroom</a> – around <a href="https://www.sciencedirect.com/topics/engineering/pulmonary-capillary">1,350 square feet (125 square meters)</a>. </p>
<h2>Getting enough oxygen</h2>
<p>If breathing is kind of like eating, why can’t you just take three breaths a day?</p>
<p>One reason is that <a href="https://climate.nasa.gov/news/2915/the-atmosphere-getting-a-handle-on-carbon-dioxide/">air on Earth</a> is only 21% oxygen – the rest is mostly nitrogen. That means you need to take five breaths just to get the equivalent of one complete lungful of oxygen. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/567971/original/file-20240104-14-2jppnf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration depicting the tunnel-like inside of a blood vessel, with vaguely donut-shaped spheres flowing through it." src="https://images.theconversation.com/files/567971/original/file-20240104-14-2jppnf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/567971/original/file-20240104-14-2jppnf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567971/original/file-20240104-14-2jppnf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567971/original/file-20240104-14-2jppnf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567971/original/file-20240104-14-2jppnf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567971/original/file-20240104-14-2jppnf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567971/original/file-20240104-14-2jppnf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Your blood can carry only so much oxygen.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/3d-render-of-red-blood-cells-or-corpuscle-flowing-royalty-free-image/1144992100">libre de droit/iStock via Getty Images</a></span>
</figcaption>
</figure>
<p>Also, when you take a breath, only some of the oxygen makes it into your bloodstream. Even though people and many animals make specialized <a href="https://teachchemistry.org/chemmatters/february-2010/the-many-colors-of-blood">proteins to grab and carry oxygen</a>, there’s a limit to how much they can hold at once. To keep your body’s oxygen levels high enough to power all your cells, you need to keep breathing.</p>
<p>Of course, once you breathe in, you also have to breathe out. The gas you breathe out is called <a href="https://learningzone.oumnh.ox.ac.uk/respiration">carbon dioxide</a>. You can think of it as the exhaust from your mitochondria engines, the leftovers once the mitochondria burn oxygen and nutrients to release energy.</p>
<h2>Other animals and plants</h2>
<p>Most living things get oxygen without lungs. </p>
<p>Many aquatic animals use gills, which are sort of like lungs turned inside out. Instead of a bunch of capillaries wrapped around air sacs, <a href="https://theconversation.com/curious-kids-how-do-gills-work-150375">gills are a bunch of capillaries</a> sticking out into the water. Just like in your lungs, the blood vessels take in oxygen from the water and release carbon dioxide.</p>
<p>Insects take in oxygen through a network of little <a href="https://askabiologist.asu.edu/how-insects-breathe">air tubes just under their skin</a>, sort of like the chimneys of a building. This system works because insects are small, so the tubes are already close enough to their cells to give them oxygen. When large insects need extra energy, they <a href="https://askabiologist.asu.edu/how-insects-breathe">pump air through the tubes</a> with their muscles.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/567945/original/file-20240104-28-4qdii8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A microscopic photo showing a green mouth shape." src="https://images.theconversation.com/files/567945/original/file-20240104-28-4qdii8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/567945/original/file-20240104-28-4qdii8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=507&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567945/original/file-20240104-28-4qdii8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=507&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567945/original/file-20240104-28-4qdii8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=507&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567945/original/file-20240104-28-4qdii8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=637&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567945/original/file-20240104-28-4qdii8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=637&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567945/original/file-20240104-28-4qdii8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=637&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A close-up look at the underside of this tomato leaf shows where the air goes in and out.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/8/85/Tomato_leaf_stomate_cropped_and_scaled.jpg">Vojtěch Dostál</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Plants have <a href="https://www.rhs.org.uk/advice/understanding-plants/how-plants-breathe">little holes in their leaves called stomata</a>. They open and close to let in air when plants need it. Plant roots need oxygen, too, which they usually get from the soil.</p>
<p>You may have heard that plants are the opposite of people: They <a href="https://www.britannica.com/story/do-plants-emit-oxygen-and-carbon-dioxide-at-night">breathe in carbon dioxide and breathe out oxygen</a>. That’s true because carbon dioxide is a crucial ingredient in <a href="https://www.britannica.com/science/photosynthesis">photosynthesis</a> – the process plants use to make their own sugar fuel – and oxygen is a byproduct. But plants’ mitochondria also need oxygen to make energy, just like yours do.</p>
<p>Even though most animals and plants don’t breathe in and out the way people do, they all have ways of getting enough oxygen. Learning how organisms solve the same problem in different ways is one of my favorite things about biology.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/219169/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christina S. Baer does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Inhaling air is how you get the oxygen your body needs to turn your food into energy. Other living things use different strategies.
Christina S. Baer, Assistant Professor of Biological Sciences, Binghamton University, State University of New York
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/217185
2024-01-29T13:34:21Z
2024-01-29T13:34:21Z
Who created the alphabet? A historian describes the millennia-long story of the ABCs
<figure><img src="https://images.theconversation.com/files/560517/original/file-20231120-20-pxbkgm.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4928%2C3260&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Creating the alphabet took thousands of years.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/english-alphabet-royalty-free-image/498549449?phrase=alphabet">kovalchuk/iStock via Getty Images Plus</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Who created the alphabet and decided its order? – Priti C., age 12, Mumbai, India</strong></p>
</blockquote>
<hr>
<p>A, B, C, D, E, F, G – makes you want to hum <a href="https://www.youtube.com/watch?v=75p-N9YKqNo">the alphabet song</a>. But there’s no real reason why people should learn these letters in this order. There are plenty of ways we could structure the alphabet; the computer keyboard in front of me provides one alternative. Plenty of other alphabets exist too, as well as languages that don’t use alphabets at all. </p>
<p>So why did we end up with this one – and who’s responsible for it? </p>
<p><a href="https://www.uml.edu/fahss/history/faculty/sancinito-jane.aspx">As a historian</a>, I love “why” questions. I often like them a lot more than “who” questions, because it’s actually really rare for a single person to change the world. Instead, most of history’s biggest innovations come from teamwork, collaboration and groups figuring out how to make life better, easier and more fun. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ZBiuJ40t4rk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A fascinating story on the origins of writing.</span></figcaption>
</figure>
<h2>What is a letter?</h2>
<p>The alphabet is a perfect example of this process. Our ABCs, known as <a href="https://kids.kiddle.co/Latin_alphabet">the Latin alphabet</a>, are the result of millions of people over thousands of years slowly working together and ultimately agreeing on which letters to use and under what circumstances. </p>
<p>To figure out why they settled on the version we have today, you first need to understand what a letter is and what an alphabet is. Then, you can trace your way back to the very first examples of both. </p>
<p>Letters are symbols, just like emojis or crosswalk signs. Letters are shapes that we – the users – associate with a sound in a particular language. </p>
<p>But many letters change sound completely when they appear in a different language. The English “H,” for example, makes a “ha” sound, but the same symbol “H” is pronounced as “en” in Russian; in the Cyrillic alphabet, “H” makes a “n” sound. </p>
<p>Even when the shape and sound of a letter stay the same within a single language, the letters themselves can have different names. In America, “Z” is called “zee,” while in Canada, the United Kingdom and pretty much every other English-speaking country, it is called “zed.” </p>
<p>All this variety is possible because letters, <a href="https://www.pearson.com/languages/community/blogs/2020/06/how-the-english-language-has-changed-over-the-decades.html">like languages, evolve and change over time</a> based on what local people do out of habit or trend or just for the fun of it. </p>
<h2>What is an alphabet?</h2>
<p>An alphabet is a collection of letter-symbols that have been more or less standardized, and which often – though not always – reflect all of the sounds made in a particular language. </p>
<p>Some languages, <a href="https://goeastmandarin.com/chinese-characters-for-kids/">like Chinese</a>, don’t have alphabets at all, using symbols to represent whole words. Others, <a href="https://www.native-languages.org/cherokee_alphabet.htm">like Cherokee</a>, use symbols that represent syllables. </p>
<p>The first alphabet was <a href="https://www.historyforkids.net/ancient-egyptian-alphabet.html">invented in ancient Egypt</a>, more than 5,000 years ago, and was developed to record religious texts. That’s where its name “hieroglyphs,” or “sacred carvings,” comes from. </p>
<p>Hieroglyphs are beautiful and they do a good job recording prayers, but they are difficult to write quickly, because they are so detailed and often take the form of <a href="https://discoveringegypt.com/egyptian-hieroglyphic-writing/egyptian-hieroglyphic-alphabet/">animals, people or day-to-day objects</a>. Over time, people developed simplified forms of each glyph so they could take notes and write informally. </p>
<p>While hieroglyphs were mostly used by priests and elites, common people, including travelers and traders from other places, <a href="https://magazine.krieger.jhu.edu/2021/10/learning-to-write-in-ancient-cultures/#:">learned informal writing</a>. These visitors realized the Egyptians had developed something useful – a way to record sales or send letters that would be clear to those who could read it but mysterious to everyone else. Many people never learned to read at all, because they did not need to or because they were denied access to education.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/gL18gFhRwq4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Once visitors learned hieroglyphs, the world took a major step toward the creation of our alphabet.</span></figcaption>
</figure>
<h2>Vowels, consonants and the letter ‘J’</h2>
<p>The most important traders in this period <a href="https://www.worldhistory.org/phoenicia/">were from Phoenicia</a> – known today as Syria, Lebanon and Israel – and they spread the alphabet to the towns and villages that surrounded the Mediterranean Sea. </p>
<p>The Phoenicians <a href="https://phoenician.org/alphabet/">established alphabetical order</a> to make it easier to learn and share with others. But the Phoenicians and Egyptians used only consonants; eventually, as people began to write more and more, and more words needed to be created to describe different things, <a href="https://teachphonics.blog/2019/10/10/what-are-vowels-and-consonants/">the Greeks adopted vowels</a>. </p>
<p>The Greek alphabet looks a lot like ours, but our letters took their final form in Italy. First the Etruscan people, and then the Romans, adapted Greek letters to fit their language. The Romans spread their language, Latin, and its alphabet all over modern Europe, the Near East and North Africa. The earliest example of the Latin alphabet in use is called <a href="https://kids.kiddle.co/Duenos_inscription">the duenos inscription</a> and comes from the sixth century BCE, 2,500 years ago. </p>
<p>Even then, the alphabet was still incomplete, because Latin didn’t have all the sounds that are common today. The most obvious is the letter “J”; even though the first month of the Roman calendar was January, it was written with an “I,” “ianuarius,” and pronounced with a “ya” sound. The “J” <a href="https://www.dictionary.com/e/j/">came into use during the Renaissance</a> – during the 1500s in Europe – two or three centuries after the “W” was added, during the Middle Ages.</p>
<p>And there’s no reason to think the alphabet might not change again. English, especially, has a habit of borrowing words from other languages, like karaoke from Japanese, cookie from Dutch and avatar from Sanskrit. Maybe, because of this borrowing, we might eventually need to add new symbols to our alphabet. In short, as the world grows more connected, the alphabet may have to adapt. It won’t be the first time.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/217185/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jane Sancinito does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Turns out ‘A’ didn’t have to be the first letter in the alphabet, nor ‘Z’ the last.
Jane Sancinito, Assistant Professor of History, UMass Lowell
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/216859
2024-01-22T13:29:39Z
2024-01-22T13:29:39Z
Why do people have different tastes in music? A music education expert explains why some songs are universally liked, while others aren’t
<figure><img src="https://images.theconversation.com/files/566074/original/file-20231215-21-eo0769.jpg?ixlib=rb-1.1.0&rect=19%2C0%2C2121%2C1409&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The types of music you listen to can reflect your personality traits. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/group-of-young-friends-listening-to-music-with-royalty-free-image/1156897122?phrase=listening+to+music&adppopup=true">Smile/Stone via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why do we have a certain taste in music, different than others? – Shirya R., age 11</strong></p>
</blockquote>
<hr>
<p>When you turn on the radio, you might hear songs you like and other songs you just skip past. But even the songs you don’t like usually have some fans. Maybe you don’t like older music, but your parents or grandparents might love it <a href="https://theconversation.com/why-do-old-people-hate-new-music-123834">because they grew up</a> with it. It’s familiar and comfortable. When you’re older, you’ll likely return to music you love too.</p>
<p>As a <a href="https://scholar.google.com/citations?user=QXuOzQIAAAAJ&hl=en">music education professor</a> who teaches music psychology, I’ve spent a lot of time thinking about music preferences and how music weaves its way through people’s brains.</p>
<p>Some composers produce music with <a href="https://theconversation.com/burt-bacharach-mastered-the-art-of-the-perfect-pop-song-and-that-aint-easy-199660">cross-generational appeal</a>. Look at the song “True Colors,” which artists have remade time and time again. It was originally released in 1986 by <a href="https://www.youtube.com/watch?v=LPn0KFlbqX8">Cyndi Lauper</a>.</p>
<p>Ten years later, Disney World’s Epcot used it as part of a <a href="https://www.youtube.com/watch?v=yUm22pobGU4">pre-show video</a>. Ten years after that, it made its way to our ears again as part of the “Trolls” movie. Now, if you scour the internet, you’ll find lots of covers of this song.</p>
<p>How can this one song appeal to many different people over time, while other songs do not? Why do some people have wildly different tastes in music, even while certain songs can unite people from a variety of backgrounds and generations? </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/3JIpIsgHqV0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">‘True Colors’ from the movie ‘Trolls,’ starring Justin Timberlake and Anna Kendrick.</span></figcaption>
</figure>
<p>Researchers have looked at <a href="https://www.ucf.edu/pegasus/your-brain-on-music/">how music works in the brain</a>. They suggest people like music with unexpected twists and turns, which sometimes cause <a href="https://theconversation.com/why-do-only-some-people-get-skin-orgasms-from-listening-to-music-59719">pleasurable physical reactions</a> <a href="https://doi.org/10.3389/fnins.2020.565815">or chills</a>. This finding suggests that humans have created and listened to music over time <a href="https://doi.org/10.1093/scan/nsw009">because it is pleasurable or rewarding</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/jyG8eWrpQ3Y?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">When you listen to music, you might get chills.</span></figcaption>
</figure>
<h2>Emotions and personality</h2>
<p>Some researchers suggest people experience emotions through music, or that they choose music based on what they want to feel. A <a href="https://doi.org/10.1037/a0022406">2011 study</a> suggests musical preference may reflect the emotions people feel when listening to music, regardless of the music’s style.</p>
<p>Some people respond to mellow and relaxing music. Others’ emotions are triggered by classical-style music. Still others emotionally react to singer-songwriter music like country, folk and some pop music. Preferences for certain types or styles of music might come from the time and place they’re first heard, or it may simply be specific to each person, regardless of what’s going on around them. </p>
<p>Though people might like certain music at one point in their lives, their music preferences change over time based on their lived experiences. When you’re struggling through a tough time, you might choose music that reflects what you wish was happening and <a href="https://doi.org/10.1007/s10824-022-09454-7">search for happy songs</a>. On the flip side, sometimes people <a href="https://doi.org/10.3389/fnhum.2015.00404">gravitate toward sad songs</a>. People want to move through grief, so they may search for songs that help them make sense of their emotions.</p>
<p>However, people’s choices don’t account for the whole picture. Musical taste goes <a href="https://doi.org/10.3389/fpsyg.2023.1062146">deeper than the music type or genre</a>. People who like pop or rock music don’t all like the same pop or rock music. </p>
<p>Studies on <a href="https://doi.org/10.1177/0956797618761659">personality and social media interaction</a> suggest your musical tastes can tell others what kind of personality you have. If someone knows what kind of music you like, that might tell them something about your personality. </p>
<p>Other <a href="https://doi.org/10.1037/pspp0000397">research suggests</a> your music preferences mirror your unique personality. So, people who already know you may be able to suggest music that you would like to hear.</p>
<p>For example, those who are more open might prefer mellow, sophisticated music like Billie Eilish’s “<a href="https://www.youtube.com/watch?v=cW8VLC9nnTo">What Was I Made For?</a>” or intense music like Imagine Dragons’ “<a href="https://www.youtube.com/watch?v=V5M2WZiAy6k">Natural</a>.”</p>
<p><a href="https://doi.org/10.1037/pspp0000397">The research found</a> extroverts may lean toward contemporary music. Agreeable people prefer unpretentious music, like Garrett Kato & Elina’s “<a href="https://www.youtube.com/watch?v=zgxNu8fBrgw">Never Alone</a>.” Conscientious people lean toward <a href="https://www.youtube.com/watch?v=0o5NTQMzNPo">unpretentious music</a> or intense music like Marshmello’s “<a href="https://www.youtube.com/watch?v=IYfejxVZ7lg">Power</a>.” People who are more anxious might prefer many different types of music.</p>
<p>People may like music by artists they like, rather than how the music sounds. Some prefer music from <a href="https://doi.org/10.1037/pspp0000293">artists who are like them</a>, especially when they can view their profiles on <a href="https://doi.org/10.1177/0956797618761659">social media</a>.</p>
<p>Why does knowing what music others like matter? Knowing about different people’s musical preferences and personalities <a href="https://www.youtube.com/watch?v=evVRxrOo5iw">can bridge gaps between people</a> with different personalities and identities. </p>
<h2>The music people stream</h2>
<p>A <a href="https://doi.org/10.1038/s41562-018-0508-z">study of 765 million songs streamed</a> by people worldwide revealed several reasons people listen to music. People’s preferences tended to change based on the time of day, their age and particular styles of music. Most people listened to more relaxing music at night but more intense music during the day. </p>
<p>Music streamed in Latin America often produced quicker physical and emotional reactions. Music streamed in Asia was usually relaxing. People who stay up later at night listened to less intense music. Depending on where participants lived, the length of the day also played a part in their music listening habits. In short, people’s environments and their individual moods shaped their preferences.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/TOhANADfR04?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Harmony in the Brain: Unraveling the Neuroscience of Music.</span></figcaption>
</figure>
<p>So, why do we have different tastes in music? People have complex personalities, and the music they like may be related to this. People’s brains work in unique ways as they process music. Some may have a physical reaction to certain music, while others may not. People may like music because a musician’s views might be like their own views. That said, some songs surprise, intrigue and entertain a wide variety of listeners, which makes them universally liked.</p>
<p>The bottom line? Each person is unique in many ways, and their musical tastes reflect that uniqueness.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/216859/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jane Kuehne does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Lots of factors can influence your music taste, from your age and where you’re from to the personality traits you have.
Jane Kuehne, Associate Professor of Music Education, Auburn University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/214919
2024-01-15T13:33:10Z
2024-01-15T13:33:10Z
What if every germ hit you at the exact same time? An immunologist explains
<figure><img src="https://images.theconversation.com/files/565348/original/file-20231212-15-ba3kr2.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2121%2C1412&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Your immune system encounters a legion of potential pathogens every day.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/woman-shielding-eyes-by-large-green-coronavirus-royalty-free-image/1250588799">Klaus Vedfelt/DigitalVision via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>What would happen if all the diseases in the world hit us at the exact same time? – Gabriella, age 12, Irving, Texas</strong></p>
</blockquote>
<hr>
<p>When I was younger, I would watch “Batman” on my black-and-white television after school. Usually, Batman would face either the Joker, the Penguin, the Puzzler, Catwoman or any one of his usual opponents. However, on some occasions, Batman would have to face them all at the same time.</p>
<p>What would happen if, like Batman, the immune system had to face all of its rivals at once?</p>
<p><a href="https://scholar.google.com/citations?user=6JOQvNwAAAAJ&hl=en">I am an immunologist</a> who teaches the fundamentals of immunology to college undergraduates. My research generally focuses on factors that regulate immune responses and prevent autoimmune diseases – conditions where the immune system attacks your own body. As a scientist studying how we build immunity against pathogens such as the virus that causes COVID-19, understanding how the immune system combats multiple threats at the same time is immensely important to me. </p>
<p>There’s no reason why you can’t come down with strep throat at the same time as when you have a cold. In fact, sometimes fighting off one enemy can leave a hole in your defenses that another opportunistic pathogen can take advantage of.</p>
<h2>BAM! Understanding the rivals</h2>
<p>The first point to consider is what your immune system protects you from. The potential bad guys <a href="https://theconversation.com/immune-cells-that-fight-cancer-become-exhausted-within-hours-of-first-encountering-tumors-new-research-210947">include cancer cells</a> and dangerous microorganisms – including bacteria, viruses, fungi and more – that cause infections. The immune system must also be careful <a href="https://theconversation.com/immune-health-is-all-about-balance-an-immunologist-explains-why-both-too-strong-and-too-weak-an-immune-response-can-lead-to-illness-215217">not to damage</a> healthy cells and beneficial microorganisms that live on and inside you. </p>
<p>You interact with <a href="https://kids.frontiersin.org/articles/10.3389/frym.2022.629355">thousands of microorganisms</a> with every breath of air you take. Is the immune system facing off against all of them? Sort of. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/565525/original/file-20231213-27-oegbgf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Microscope images of two T regulatory cells wrapped around an antigen-presenting cell" src="https://images.theconversation.com/files/565525/original/file-20231213-27-oegbgf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565525/original/file-20231213-27-oegbgf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565525/original/file-20231213-27-oegbgf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565525/original/file-20231213-27-oegbgf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565525/original/file-20231213-27-oegbgf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565525/original/file-20231213-27-oegbgf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565525/original/file-20231213-27-oegbgf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">T regulatory cells (red) determine whether an immune response should be mounted.</span>
<span class="attribution"><a class="source" href="https://flic.kr/p/SjQFf7">NIAID/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>It takes a <a href="https://theconversation.com/how-does-fever-help-fight-infections-theres-more-to-it-than-even-some-scientists-realize-210240">tremendous amount of energy</a> to fight a battle once a rival gains a foothold within your blood or tissues, so your immune system works to <a href="https://theconversation.com/how-do-viruses-get-into-cells-their-infection-tactics-determine-whether-they-can-jump-species-or-set-off-a-pandemic-216139">prevent it from getting in the body</a> in the first place. Your skin, <a href="https://theconversation.com/why-do-our-noses-get-snotty-when-we-are-sick-a-school-nurse-explains-the-powers-of-mucus-212949">snot</a>, saliva and <a href="https://theconversation.com/can-you-cry-underwater-205464">tears</a> form a critical <a href="https://www.ncbi.nlm.nih.gov/books/NBK279396/">first line of defense</a>. This is why <a href="https://doi.org/10.1089%2Fsur.2013.134">burn victims</a> who lose too much skin often die from overwhelming infection – their defensive barriers are too compromised and pathogens pour in.</p>
<p>The immune system greatly prefers <a href="https://theconversation.com/a-pediatric-nurse-explains-the-science-of-sneezing-160970">catching a microbe in snot</a> and blowing it out of your nose, or giving you time to wash it off the skin of your hands, over having to wage a cellular war. Gathering an army of <a href="https://theconversation.com/coronavirus-b-cells-and-t-cells-explained-141888">immune cells</a> to fight pathogens takes a lot of energy and makes you feel awful. </p>
<p>For example, the immune system <a href="https://theconversation.com/how-does-fever-help-fight-infections-theres-more-to-it-than-even-some-scientists-realize-210240">increases your body temperature</a> to make it an uncomfortable place for microorganisms to live and grow, but that fever can also make you want to lie down for days.</p>
<h2>BOOM! Where are their weaknesses?</h2>
<p>When Batman faced multiple opponents, he would find a weakness shared by all of the opponents and target it to foil their plans. The immune system uses the exact same strategy.</p>
<p>Certain microbes are considered pathogens largely because they are in the wrong place – such as inside your body instead of on your skin – and causing damage. Pathogens have specific parts on their surfaces called <a href="https://doi.org/10.1038/s41392-021-00687-0">pathogen associated molecular patterns, or PAMPs</a>.</p>
<p>Very importantly, your body doesn’t make PAMPS. This means if your immune system comes across a PAMP, it knows it isn’t supposed to be there and will mount an attack. Because the same PAMP is present on many different pathogens, a strategy to combat one PAMP can defeat many pathogens.</p>
<p>There are molecules in cells all over your body that can recognize PAMPS and destroy anything those PAMPS are on. It’s as though your immune system set up booby traps that can only attack your enemies.</p>
<p>Many of those booby traps are <a href="https://doi.org/10.1038/35100529">toll-like receptors</a>. This family of molecules is located on the surface and inside of many of your cells. Once microbes contact these booby traps, they trigger an alarm that warn other cells of potential danger. In technical terms, this alarm is <a href="https://theconversation.com/what-is-inflammation-two-immunologists-explain-how-the-body-responds-to-everything-from-stings-to-vaccination-and-why-it-sometimes-goes-wrong-193503">called inflammation</a>.</p>
<h2>SPLAT! Raising an army of defenders</h2>
<p>Whereas Batman would need to think of a new strategy to combat the Joker, the Penguin and Catwoman, your immune system devised a plan long ago. </p>
<p>When the virus that causes COVID-19 emerged in 2019, it was something people’s immune systems likely had never seen before. However, some people already had immune cells that could target components of the virus. How is that possible?</p>
<p>The immune system makes many immune cells that are specific to antigens, or unique and recognizable parts of cancers and microorganisms, it hasn’t encountered before. This occurs through a process where pieces of your DNA <a href="https://doi.org/10.1038/nri2941">randomly recombine to form</a> unique immune cell receptors. The DNA in each of these immune cells is different from the DNA in any other cell in your body. Researchers believe that each person can generate <a href="https://www.ncbi.nlm.nih.gov/books/NBK27140/">at least a trillion different combinations</a> of immune receptors, which is <a href="https://doi.org/10.1038/nrmicro2644">more than the number of pathogens</a> an average person would ever face in their lifetime overall.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Na-Zc-xWCLE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Your immune system can churn out billions of unique antibodies.</span></figcaption>
</figure>
<p>Although the immune system makes a lot of immune cells, most of them aren’t used because you’re not exposed to the antigen they’re made to recognize. However, when an immune cell recognizes an antigen, it rapidly <a href="https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Boundless)/11%3A_Immunology/11.07%3A_Antibodies/11.7C%3A_Clonal_Selection_of_Antibody-Producing_Cells">makes many copies of itself</a>. Since pathogens can also multiply rapidly, clonal selection allows you to rapidly raise an army to fight them.</p>
<p>Usually this strategy works well with <a href="https://theconversation.com/when-covid-19-or-flu-viruses-kill-they-often-have-an-accomplice-bacterial-infections-187056">one or two coinfections</a>, such as if you have the common cold and an eye infection at the same time. But what if you were infected with a trillion pathogens at the same time? It would take a tremendous amount of energy and time to build an appropriate army against each microorganism all at once. Unfortunately, the immune system likely would be overwhelmed by this challenge, and you would probably die. </p>
<p>Fortunately, your immune system – like Batman – usually figures out the best way to shift a battle against rivals to its favor, pulling out a victory in the final minutes of the episode.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/214919/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joseph Larkin III receives funding from the Grayson Jockey Research Foundation, The National Institutes of Health, and industry. </span></em></p>
Your immune system is often able to fend off pathogens it’s never seen before. But defending your body against all of them all at once is a tough challenge.
Joseph Larkin III, Associate Professor of Microbiology and Cell Science, University of Florida
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/209196
2024-01-08T13:36:16Z
2024-01-08T13:36:16Z
What happens to the ocean if we take out all the fish? A marine ecologist explains the complex roles fish play in their ecosystem
<figure><img src="https://images.theconversation.com/files/543088/original/file-20230816-19-h6b36a.jpg?ixlib=rb-1.1.0&rect=6%2C12%2C2038%2C1348&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Fish swim in a reef at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/UNBiodiversity/3ead5d56c624402893c0df11ab789657/photo?Query=ocean%20fish&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=262&currentItemNo=31&vs=true">AP Photo/Jacob Asher </a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>What would happen to the ocean if we took out all the fish? – Reny, age 12</strong></p>
</blockquote>
<hr>
<p>The ocean is massive and covers most of the surface of our planet. In addition to its size, it’s packed with life, ranging from an astounding diversity of plants, microbes, worms, corals and crabs to squids, whales and, yes, even fish. The ocean is full of fish, so much so that they make up the <a href="https://doi.org/10.1073/pnas.1711842115">second-largest amount of all carbon</a> – the material that makes up living things – in the entire animal kingdom. They’re just behind the group containing insects and crustaceans.</p>
<p>Most people only interact with the ocean from a beach or in a boat, so it can be hard to wrap your head around how many fish there really are. But the ocean is swarming with them, from its surface <a href="https://www.nbcnews.com/news/world/deepest-ever-fish-filmed-japan-scientists-rcna77858">to its depths</a>. </p>
<p>These fish also come in all kinds of shapes and sizes, ranging from the tiny sardines, guppies and blennies that you might <a href="https://www.palmbeachpost.com/story/opinion/columns/guest/2020/01/25/point-of-view-call-for-more-diversity-not-only-more-fish-in-marine-protected-areas/112150854/">see on a coral reef</a> to massive tunas and whale sharks that you might find <a href="https://www.fisheries.noaa.gov/feature-story/surface-slicks-are-pelagic-nurseries-diverse-ocean-fauna">out in the open ocean</a>. </p>
<p>These fish perform all kinds of <a href="https://doi.org/10.1002/ecs2.4288">roles in their ecosystems</a> that support the lives of other organisms around them. If they disappeared one day, the ocean would look very different.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">School of slopehead parrotfish.</span>
<span class="attribution"><span class="source">NOAA, Kevin Lino</span></span>
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</figure>
<p>I’m a <a href="https://koryevans.weebly.com/">scientist who studies fish</a>, their diversity and all the ways they contribute to ocean environments.</p>
<h2>Fish as food</h2>
<p>Fish play important roles as both <a href="https://www.noaa.gov/education/resource-collections/marine-life/aquatic-food-webs">predators and prey</a> in ocean ecosystems. Thousands of species throughout the ocean and terrestrial ecosystems rely on fish for food – <a href="https://www.fisheries.noaa.gov/feature-story/economic-importance-seafood">including people</a>. </p>
<p>In coral reef ecosystems, small fish are eaten by larger fish and other marine animals. This means the little fish form the base of the food web – they provide energy to the bigger fish and other creatures. </p>
<figure class="align-center ">
<img alt="Conceptual food web of a coral reef ecosystem identifying key functional groups." src="https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=569&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=569&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=569&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=715&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=715&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=715&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Links between different species of coral reef animals.</span>
<span class="attribution"><span class="source">Global Change Biology, Rogers et al., 2015</span></span>
</figcaption>
</figure>
<p>Outside of the water, many birds, mammals and reptiles eat fish and rely on them as an <a href="https://doi.org/10.1016/S0921-8009(99)00015-4">essential source of protein</a>. </p>
<p>Even land plants can benefit from the presence of fish. On the western coast of the United States, salmon returning to small streams after spending several years at sea function as a conveyor belt of nutrients. The salmon feed not only animals that catch them, like bears, but also the plants that border the streams. Studies have shown that some plants get <a href="https://www.adfg.alaska.gov/index.cfm?adfg=wildlifenews.view_article&articles_id=407">70% of their nitrogen</a> from salmon that die on or near the river banks. </p>
<p>Humans also depend on fish as a food source. Fish and other seafood products are an important protein source for <a href="https://www.nature.org/en-us/what-we-do/our-priorities/provide-food-and-water-sustainably/food-and-water-stories/global-fisheries/">nearly 3 billion people</a>. Human populations have been eating and following fish around the world for <a href="https://doi.org/10.1073/pnas.1710186114">thousands of years</a>. </p>
<h2>Fish maintain habitats</h2>
<p>Fish are also more than just food. As fish themselves forage for food, they can create and maintain important <a href="https://doi.org/10.1007/s00338-006-0112-y">habitats for other organisms</a>. In coral reef ecosystems, plant-eating fish control the growth of algae by constantly grazing it down. Without the help of these herbivores, or plant-eating fish, the algae would rapidly grow and smother the coral, effectively killing it. </p>
<p>One type of herbivorous fish, the parrotfish, <a href="https://ocean.si.edu/ocean-life/fish/tough-teeth-and-parrotfish-poop">feeds directly on the corals</a>. At first, this may seem bad for the corals, but the grazing done by parrotfish can actually increase a coral colony’s rate of growth. And <a href="https://ocean.si.edu/ocean-life/fish/tough-teeth-and-parrotfish-poop">the poop</a> – yes, the poop – from parrotfish has been shown to be <a href="https://doi.org/10.1016/j.tim.2022.03.006">particularly nutritious</a> for corals. Parrotfish poop also forms part of the <a href="https://ocean.si.edu/ocean-life/fish/tough-teeth-and-parrotfish-poop">beautiful white sand beaches</a> that you may have enjoyed on a family vacation.</p>
<p>Other fish create habitats for other animals and influence their environment by <a href="https://www.ingentaconnect.com/content/umrsmas/bullmar/1986/00000038/00000001/art00006">disturbing sand</a> while they feed. By moving the sand around, they’re exposing tiny organisms hiding in the sand, which other animals can eat. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/_pN5-96nduge?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Some fish sift through sand to find their food. That creates more opportunities for other creatures to find food in the sand.</span></figcaption>
</figure>
<p>Despite the fact that many types of fish are confined to the ocean, their presence can be felt across many habitats. They can directly and indirectly affect the lives of the organisms that depend on them for food and shelter. Without fish, Earth would gradually lose its beautiful white sand beaches, the coral reef ecosystems would be overgrown with algae, lots of people would run out of food to eat, and we would lose some of the planet’s most fascinating creatures.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/209196/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kory Evans receives funding from National Science Foundation. </span></em></p>
There are so many fish in the ocean that if you took them out, important habitats and food sources for many creatures would be lost.
Kory Evans, Assistant Professor of BioSciences, Rice University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/217241
2023-12-18T13:23:27Z
2023-12-18T13:23:27Z
Why are some black holes bigger than others? An astronomer explains how these celestial vacuums grow
<figure><img src="https://images.theconversation.com/files/562536/original/file-20231129-23-ug9ynd.jpg?ixlib=rb-1.1.0&rect=5%2C15%2C3429%2C2863&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Black holes use gravity to pull matter into them. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/HungryBlackHole/4cd9b7c1c318427ba2f3b78c77cfe6de/photo?Query=black%20hole&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=418&currentItemNo=7&vs=true&vs=true">NASA/Chandra X-ray Observatory/M.Weiss via AP</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why are there small and big black holes? Also, why are some black holes invisible and others have white outlines? – Sedra and Humaid, Abu Dhabi, United Arab Emirates</strong></p>
</blockquote>
<hr>
<p><a href="https://theconversation.com/the-scariest-things-in-the-universe-are-black-holes-and-here-are-3-reasons-148615">Black holes</a> are dense astronomical objects with gravity so strong that nothing, not even light, can escape. Anything that crosses the boundary of a black hole’s gravitational influence, called the event horizon, will fall into the black hole. Inside this deep, dense pit, it is never to be seen again. </p>
<p>Black holes litter the universe. Some smaller black holes are sprinkled randomly throughout galaxies like our Milky Way. Other gigantic ones, called <a href="https://theconversation.com/supermassive-black-hole-at-the-center-of-our-galaxy-may-have-a-friend-128295">“supermassive” black holes</a>, lie at the centers of galaxies. Those can weigh anywhere between a million to a billion times the mass of our Sun. So you might be wondering: How can astronomers possibly see something so dark and so big?</p>
<p>I am an <a href="https://jackiechampagne.com">astronomer</a> who studies the very first supermassive black holes that formed in our universe. I want to understand how black holes form and what kinds of astrophysical neighborhoods they grow up in.</p>
<h2>Types of black holes</h2>
<p>Let’s talk about how black holes begin their lives. Two famous scientists, <a href="https://www.britannica.com/biography/Albert-Einstein">Albert Einstein</a> and <a href="https://www.britannica.com/biography/Karl-Schwarzschild">Karl Schwarzchild</a>, first pitched the <a href="https://www.astronomy.com/science/a-brief-history-of-black-holes/">idea of a black hole</a>. They thought that when a large star dies, its core might shrink and shrink until it <a href="https://universe.nasa.gov/black-holes/types/">collapses under its own weight</a>. This is what we astronomers call a “<a href="https://www.nasa.gov/image-article/stellar-mass-black-hole/">stellar mass black hole</a>,” which is just another way of saying it’s comparatively very small.</p>
<p>Stellar mass black holes are only a few times bigger than our Sun. Supermassive black holes are more of a mystery, though. They are many millions of times heavier than our Sun, and they are packed into a small area that’s about the size of our solar system. Some scientists think supermassive black holes might form by <a href="https://science.nasa.gov/astrophysics/focus-areas/black-holes/">many stars colliding and collapsing at once</a>, while others think they might have already started growing several billion years ago. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tMax0KgyZZU?wmode=transparent&start=13" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Stars at the center of the Milky Way are orbiting around an invisible object, a supermassive black hole, like planets orbit around the Sun. Credit: Andrea Ghez/UCLA/W.M. Keck Observatory.</span></figcaption>
</figure>
<h2>Growing black holes</h2>
<p>What do black holes look like? Most of the time, they are not actively growing, so they are invisible. But we can tell they’re there because <a href="https://theconversation.com/2020-nobel-prize-in-physics-awarded-for-work-on-black-holes-an-astrophysicist-explains-the-trailblazing-discoveries-147614">stars can still orbit around them</a>, just like Earth around the Sun. </p>
<p>When something is orbiting an invisible object at high speeds, scientists know there <a href="https://theconversation.com/2020-nobel-prize-in-physics-awarded-for-work-on-black-holes-an-astrophysicist-explains-the-trailblazing-discoveries-147614">must be a massive black hole</a> in the middle. This is the case for the closest supermassive black hole to us, which lies at the center of the Milky Way – safely millions of miles away from you.</p>
<p>Meanwhile, when a hungry black hole is eating up gas in a galaxy, it heats that gas up until you can see a <a href="https://universe.nasa.gov/black-holes/anatomy/">glowing ring</a> of X-rays, optical light and infrared light around the black hole. Once it exhausts all of the fuel near the event horizon, the light dies down once again and it becomes invisible. </p>
<h2>Outlines around black holes</h2>
<p>One of the most famous “white outlines” is the <a href="https://cerncourier.com/a/building-gargantua/">image of a black hole</a> from <a href="https://www.imdb.com/title/tt0816692/">the movie “Interstellar</a>.” In that movie, they were trying to show the white-hot, glowing ring of gases that are falling into the actively growing black hole. </p>
<p>In real life, we don’t get such a close-up view. The best image of the ring around a real black hole comes from the <a href="https://eventhorizontelescope.org/">Event Horizon Telescope</a>, showing scientists the supermassive black hole at the center of a <a href="https://science.nasa.gov/resource/first-image-of-a-black-hole/">galaxy called M87</a>. It might look blurry to you, but this doughnut is actually the sharpest image ever taken of something so far away.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A blurry golden circle against a black background." src="https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=439&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=439&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=439&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The first-ever image of a black hole was taken by the Event Horizon Telescope in 2019. You can see the light as it bends around the intense gravity of the black hole at the center of a galaxy called M87. It might look blurry, but this is the equivalent of being able to read a newspaper on a table in Paris if you were standing in New York.</span>
<span class="attribution"><a class="source" href="https://eventhorizontelescope.org/press-release-april-10-2019-astronomers-capture-first-image-black-hole">Event Horizon Telescope</a></span>
</figcaption>
</figure>
<p>There are lots of types of black holes out there in the universe. Some are small and invisible, and some grow to gigantic proportions by eating up stuff inside a galaxy and shining bright. But don’t worry, black holes can’t just keep sucking in everything in the universe – eventually there is nothing close enough to the black hole to fall in, and it will become invisible again. So you are safe to keep asking questions about black holes. </p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/217241/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jaclyn Champagne receives funding from the National Science Foundation and the Space Telescope Science Institute. </span></em></p>
Pictures of black holes have a white outline around them when photographed, due to one of black holes’ unique and key features.
Jaclyn Champagne, JASPER Postdoctoral Researcher, University of Arizona
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/216148
2023-12-11T13:12:05Z
2023-12-11T13:12:05Z
Why do people have wisdom teeth?
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why do people have wisdom teeth? – Jack J., age 17, Dedham, Massachusetts</strong></p>
</blockquote>
<hr>
<p>Wisdom teeth are the third set of molars located at the very back of the mouth. They look just like the first and second molars, but can sometimes be a little smaller. </p>
<p>They are commonly called wisdom teeth because they are the last of the 32 permanent teeth to appear, emerging <a href="https://doi.org/10.1159/000151214">between 17 and 25 years of age</a>, when you are older and wiser.</p>
<p>You might know that <a href="https://doi.org/10.7717/peerj.10367">not everyone grows</a> all four wisdom teeth. You might also know many people get them pulled. So it’s fair to wonder – why do humans even have them? </p>
<p><a href="https://scholar.google.com/citations?hl=en&user=0lZq0kYAAAAJ">We</a> <a href="https://scholar.google.com/citations?hl=en&user=GYMrNdIAAAAJ">study</a> teeth and can tell you the answer has a lot to do with the distant past – and a bit about the present day, too. </p>
<h2>More powerful jaws</h2>
<p>Just like you have many features in common with the people you’re related to, humans share features with their extended family – the primates. <a href="https://doi.org/10.3389/fdmed.2023.1158482">Monkeys, gorillas and chimpanzees</a> all have wisdom teeth. </p>
<p>A few million years ago, early human ancestors had larger jaws and teeth than humans do today. For example, a species called <em>Australopithecus afarensis</em>, <a href="https://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-afarensis">nicknamed Lucy’s species</a> after a <a href="https://www.nature.com/scitable/knowledge/library/lucy-a-marvelous-specimen-135716086/">famous fossil specimen called Lucy</a>, lived roughly 3 million to 4 million years ago. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A fossilized jaw showing powerful molars and some broken and missing front teeth." src="https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560510/original/file-20231120-21-9261y5.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A fossilized jaw from the extinct human ancestor, <em>Australopithecus afarensis</em>, also known as Lucy’s species.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Australopithecus_afarensis_jaw_-_Fossils_in_the_Arppeanum_-_DSC05509.JPG">Daderot/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The jaw and teeth of an <em>Australopithecus afarensis</em> individual were quite a bit <a href="https://doi.org/10.1002/ajpa.21183">larger and thicker</a> than your own. They had three <a href="https://doi.org/10.1007/s12052-010-0249-6">big molar teeth with thick enamel</a>. The fossil skulls of some of these very early humans also show evidence of <a href="https://doi.org/10.1002/ajpa.21183">powerful chewing muscles</a>.</p>
<h2>Changes in diet</h2>
<p>Scientists think more robust jaws and teeth were needed because the foods early human ancestors ate, like raw meat and <a href="https://doi.org/10.1016/j.jhevol.2017.10.013">plants</a>, were much more difficult to chew than food is today. Researchers look at things like <a href="https://doi.org/10.1038/sj.bdj.2014.353">marks and microscopic wear patterns</a> <a href="https://theconversation.com/tooth-be-told-millions-of-years-of-evolutionary-history-mark-those-molars-71428">on fossilized teeth</a> to figure out <a href="https://press.princeton.edu/books/hardcover/9780691160535/evolutions-bite">what extinct ancestors may have eaten</a>. </p>
<p>Today’s food is much softer than it was in the past due to many factors, including <a href="https://doi.org/10.1111/joim.13011">agriculture</a>, <a href="https://doi.org/10.1007/s12110-009-9075-3">cooking</a> and <a href="https://doi.org/10.1038/nplants.2016.194">food storage</a>. Softer, easier-to-chew food means teeth have a less challenging job. As a result, modern human jaws have evolved to be <a href="https://doi.org/10.1038/s41559-019-0865-7">smaller and faces to be flatter</a> than our extinct ancestors’ were, because our meals don’t require the same big, sharp teeth that theirs did. </p>
<p>Given these changes, which took place very slowly over millions of years, the third molars – wisdom teeth – might not be as important now as they once were.</p>
<h2>Missing wisdom teeth</h2>
<p>About <a href="https://www.ncbi.nlm.nih.gov/books/NBK572295/">25% of people today are missing at least</a> one wisdom tooth completely, meaning it never formed at all. While people occasionally don’t grow other teeth, it’s <a href="https://pubmed.ncbi.nlm.nih.gov/34292692/">much more common for wisdom teeth</a>. </p>
<p>Scientists are not sure why this is the case, but it <a href="https://doi.org/10.1007/s11914-022-00761-8">may have to do with the genes</a> <a href="https://doi.org/10.3390/genes9050255">you inherit from your parents</a>. Some scientists have argued that the <a href="https://doi.org/10.1093/ejo/cjad057">lack of wisdom teeth is an advantage</a> for modern, smaller-jawed humans. It’s certainly easier to fit fewer teeth into a smaller jaw.</p>
<p>Sometimes, due to lack of space, wisdom teeth can get stuck inside the jawbone and never fully come up – or they only partially emerge. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A radiograph showing a back molar growing sideways into its neighbor." src="https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/560516/original/file-20231120-18-71m6oo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An impacted wisdom tooth will never come up properly.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Impacted_Wisdom_Tooth_aka_Lower_Right_Third_Molar_48_RVG_IOPA_Xray.jpg">Nizil Shah/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>A so-called impacted wisdom tooth happens <a href="https://pubmed.ncbi.nlm.nih.gov/2205795/">more often in the lower jaw</a> than in the upper jaw. In cases where wisdom teeth are only partially up, people can sometimes experience pain, tooth decay or gum inflammation, which is why they have them pulled by a dentist.</p>
<p>But wisdom teeth don’t usually need to be removed if they are fully erupted in the mouth, positioned correctly and healthy.</p>
<p>Dentists can examine your mouth to see if your wisdom teeth are present, or look at X-ray pictures of your jaw if these last molars haven’t yet emerged and you suspect they may be impacted.</p>
<p>Dentists can also advise you if any treatment – or removal – is recommended for your wisdom teeth. In the meantime, <a href="https://www.mouthhealthy.org/all-topics-a-z/brushing-your-teeth">brushing</a> at least twice a day and <a href="https://www.mouthhealthy.org/all-topics-a-z/flossing">flossing</a> daily will help keep all your teeth healthy. </p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/216148/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ariadne Letra receives funding from the National Institute for Dental and Craniofacial Research.</span></em></p><p class="fine-print"><em><span>Seth M. Weinberg receives funding from the National Institutes of Health. </span></em></p>
Two dental experts explain that these furthest-back molars may be a not-so-necessary leftover from early human evolution.
Ariadne Letra, Professor of Dental Medicine, University of Pittsburgh
Seth M. Weinberg, Professor of Oral and Craniofacial Sciences and Human Genetics, University of Pittsburgh
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/217885
2023-12-04T13:25:52Z
2023-12-04T13:25:52Z
Why isn’t there any sound in space? An astronomer explains why in space no one can hear you scream
<figure><img src="https://images.theconversation.com/files/560865/original/file-20231121-23-g49y80.png?ixlib=rb-1.1.0&rect=0%2C5%2C1957%2C1992&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Matter in deep space is very spread out, which makes it impossible for any sound waves to travel. </span> <span class="attribution"><a class="source" href="https://webbtelescope.org/contents/media/images/2022/038/01G7JGTH21B5GN9VCYAHBXKSD1?news=true">NASA, ESA, CSA, STScI</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>How far can sound travel through space, since it’s so empty? Is there an echo in space? – Jasmine, age 14, Everson, Washington</strong></p>
</blockquote>
<hr>
<p>In space, no one can hear you scream.</p>
<p>You may have heard this saying. It’s the tagline from the famous 1979 science fiction movie “<a href="https://screenrant.com/space-no-one-hear-scream-alien-movie-origin/">Alien</a>.” It’s a scary thought, but is it true? The simple answer is yes, no one can hear you scream in space because there is no sound or echo in space.</p>
<p>I’m a <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">professor of astronomy</a>, which means I study space and how it works. Space is silent – for the most part.</p>
<h2>How sound works</h2>
<p>To understand why there’s no sound in space, first consider how sound works. <a href="https://www.scienceworld.ca/resource/sound/">Sound is a wave</a> of energy that moves through a solid, a liquid or a gas. </p>
<p>Sound is <a href="https://www.britannica.com/science/longitudinal-wave">a compression wave</a>. The energy created when your vocal cords vibrate slightly compresses the air in your throat, and the compressed energy travels outward. </p>
<p>A good analogy for sound is a <a href="https://www.scienceworld.ca/resource/modelling-sound-wave/">Slinky toy</a>. If you stretch out a Slinky and push hard on one end, a <a href="https://www.youtube.com/watch?v=GKzpVUUrwM8">compression wave travels</a> down the Slinky.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fMJrtheQfZw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Slinky toys can demonstrate how sound waves, a type of compression wave, work.</span></figcaption>
</figure>
<p>When you talk, your vocal cords vibrate. They jostle air molecules in your throat above your vocal cords, which in turn jostle or bump into their neighbors, causing a sound to come out of your mouth. </p>
<p>Sound moves through air the same way it moves through your throat. Air molecules near your mouth bump into their neighbors, which in turn bump into their neighbors, and the sound moves through the air. The <a href="https://www.grc.nasa.gov/www/k-12/BGP/sound.html">sound wave travels quickly</a>, about 760 miles per hour (1,223 kilometers per hour), which is faster than a commercial jet.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/sQZtKAPv7lI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Sound waves are created when matter vibrates.</span></figcaption>
</figure>
<h2>Space is a vacuum</h2>
<p>So what about in space?</p>
<p>Space is a vacuum, which means it contains almost no matter. The word vacuum <a href="https://www.etymonline.com/word/vacuum">comes from the Latin word for empty</a>.</p>
<p>Sound is carried by atoms and molecules. In space, with no atoms or molecules to carry a sound wave, there’s no sound. There’s nothing to get in sound’s way out in space, but there’s nothing to carry it, so it doesn’t travel at all. No sound also means no echo. <a href="https://theconversation.com/curious-kids-what-makes-an-echo-109141">An echo</a> happens when a sound wave hits a hard, flat surface and bounces back in the direction it came from.</p>
<p>By the way, if you were caught in space outside your spacecraft with no spacesuit, the fact that no one could hear your cry for help is the least of your problems. Any air you still had in your lungs would expand because it was at higher pressure than the vacuum outside. Your lungs would rupture. In a mere <a href="https://www.space.com/how-long-could-you-survive-in-space-without-spacesuit">10 to 15 seconds</a>, you’d be unconscious due to a lack of oxygen. </p>
<h2>Sound in the solar system</h2>
<p>Scientists have wondered how human voices would sound on our nearest neighboring planets, Venus and Mars. This experiment is hypothetical because <a href="https://www.space.com/16907-what-is-the-temperature-of-mars.html">Mars is usually below freezing</a>, and its atmosphere is <a href="https://science.nasa.gov/mars/facts/">thin, unbreathable carbon dioxide</a>. <a href="https://science.nasa.gov/venus/facts/">Venus is even worse</a> – its air is hot enough to melt lead, with a thick carbon dioxide atmosphere.</p>
<p>On Mars, your voice would sound tinny and hollow, like the <a href="https://www.youtube.com/watch?v=cE26bD_-hN4">sound of a piccolo</a>. <a href="https://www.nbcnews.com/science/cosmic-log/how-would-you-sound-mars-flna659387">On Venus</a>, the pitch of your voice would be much deeper, like the sound of a booming bass guitar. The reason is the thickness of the atmosphere. On Mars the thin air creates a high-pitched sound, and on Venus the thick air creates a low-pitched sound. The team that worked this out <a href="https://www.southampton.ac.uk/news/2012/04/the-sounds-of-mars-and-venus.page">simulated other solar system sounds</a>, like a waterfall on Saturn’s moon Titan.</p>
<h2>Deep space sounds</h2>
<p>While space is a good enough vacuum that normal sound can’t travel through it, it’s actually not a perfect vacuum, and it does have some particles floating through it.</p>
<p><a href="https://www.universetoday.com/34074/interplanetary-space/">Beyond the Earth</a> and its atmosphere, there are five particles in a typical cubic centimeter – the volume of a sugar cube – that are mostly hydrogen atoms. By contrast, the air you are breathing is 10 billion billion (10<sup>19)</sup> times more dense. The density goes down with distance from the Sun, and in <a href="https://www.space.com/interstellar-space-definition-explanation">the space between stars</a> there are 0.1 particles per cubic centimeter. In vast <a href="https://www.livescience.com/why-is-space-a-vacuum.html">voids between galaxies</a>, it is a million times lower still – fantastically empty.</p>
<p>The voids of space are kept very hot by radiation from stars. The very spread-out matter found there is in a physical state <a href="https://www.psfc.mit.edu/vision/what_is_plasma">called a plasma</a>. </p>
<p>A plasma is a gas in which electrons are separated from protons. In a plasma, the <a href="https://www.iflscience.com/is-there-really-no-sound-in-space-69612">physics of sound waves get complicated</a>. Waves travel much faster in this low-density medium, and their wavelength is much longer.</p>
<p>In 2022, NASA released a <a href="https://www.vice.com/en/article/y3p3dv/nasa-has-captured-actual-sound-in-space-and-its-honestly-terrifying">spectacular example of sound in space</a>. It used X-ray data to make an audible recording that represents the way a massive black hole stirs up plasma in the Perseus galaxy cluster, 250 million light years from Earth. The black hole itself emits no sound, but the diffuse plasma around it carries very long wavelength sound waves.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1561442514078314496"}"></div></p>
<p>The natural sound is far too low a frequency for the human ear to hear, 57 octaves below middle C, which is the middle note on a piano and in the middle of the range of sound people can hear. But after raising the frequency to the audible range, the result is chilling – it’s the sound of a black hole growling in deep space.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/217885/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation. </span></em></p>
Sound needs matter to propagate, so the vast vacuum of space is not just empty − it’s silent.
Chris Impey, University Distinguished Professor of Astronomy, University of Arizona
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/213211
2023-11-27T13:40:22Z
2023-11-27T13:40:22Z
Why are bullies so mean? A youth psychology expert explains what’s behind their harmful behavior
<figure><img src="https://images.theconversation.com/files/555404/original/file-20231023-19-fns0q3.jpg?ixlib=rb-1.1.0&rect=10%2C0%2C6781%2C3574&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Spreading rumors about others is one form of bullying.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/young-sad-teenage-girl-feeling-lonely-and-excluded-royalty-free-image/1413738081?phrase=bullying+school&adppopup=true">LumiNola/E+ via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why are bullies so mean? – Daisy, age 9, Lake Oswego, Oregon</strong></p>
</blockquote>
<hr>
<p>Being bullied can make your life miserable, and decades of research prove it: Bullied children and teens <a href="https://doi.org/10.1080/00405841.2016.1148988">are at risk</a> for anxiety, depression, dropping out of school, peer rejection, social isolation and self-harm.</p>
<p>Adults can be bullied too, often at a job, and they <a href="https://doi.org/10.1016/j.avb.2020.101508">may suffer just as much</a> as kids do. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/iFlrCuSyhvU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">You can help stop bullying in your school or workplace.</span></figcaption>
</figure>
<p><a href="https://www.cehd.udel.edu/faculty-bio/sara-goldstein/">I’m a professor</a> who studies child and adolescent development. That includes learning how people become bullies – and how they can be stopped. </p>
<p>First, let’s <a href="https://psycnet.apa.org/fulltext/2015-20405-003.pdf">define what bullying is</a>: It’s mean-spirited, harmful behavior by someone with more power or status – like a popular kid at school or a supervisor at work – who repeatedly picks on, harasses, irritates or injures a person with less power or status. </p>
<p><a href="https://doi.org/10.1007/978-3-031-13134-9_3">Bullying can take many forms</a> – physical, like pushing, shoving and hitting; relational, such as spreading rumors, keeping somebody out of a friend group or just rude remarks; or sexual harassment and stalking behavior. </p>
<p>Sometimes, bullies target someone because of their race, religion, sexual orientation or appearance. People from the LGBTQ+ community, or who are overweight, or with a physical or developmental disability are <a href="https://doi.org/10.1016/j.dr.2018.02.001">more likely to be bullied</a>. As a result, they <a href="https://doi.org/10.1007/978-3-031-13134-9_3">may develop mental health problems</a>, including depression, anxiety and self-harming behavior.</p>
<h2>So why do bullies do it?</h2>
<p>People learn how to bully others early on through what psychologists call modeling and social learning. This means bullies see other people bullying and they essentially model, or copy, this aggressive behavior. </p>
<p>Media is <a href="https://doi.org/10.1002/9781119011071.iemp0166">a big culprit here</a>. When mean or violent conduct is glamorized and gamified in music, video games, TV and movies, bullies will imitate what they see and hear, especially if it seems cool or if it’s rewarded. </p>
<p>Family <a href="https://doi.org/10.1097/CHI.0b013e31819cb017">is also an influence</a>. If children grow up in a home without kindness and closeness, but with plenty of physical punishment and heavy conflict – including parents fighting with each other – then children view this behavior as acceptable. They can go on to treat their peers this way. </p>
<p>A similar thing happens when a kid falls into a group of friends who are bullies; they become <a href="https://doi.org/10.1017/S095457941900083X">more likely to bully others themselves</a>. To say it another way, they bully because they think it makes them look cool in front of their friends.</p>
<p>And bullies bully for <a href="https://www.healthdirect.gov.au/bullying#:%7E">lots of other reasons</a>. Some do it because it makes them feel better about themselves when they put other people down. Other bullies discovered that force and intimidation worked for them in the past, so it’s a go-to strategy to get what they want. Still others simply have difficulty controlling themselves and can’t calm down when they’re angry. </p>
<p>And with some bullies, it’s just a way to get ahead. For instance, an adult bully in the workplace <a href="https://www.routledge.com/Bullying-and-Harassment-in-the-Workplace-Theory-Research-and-Practice/Einarsen-Hoel-Zapf-Cooper/p/book/9781138615991">may spread an embarrassing rumor</a> about a co-worker to keep a rival from being promoted. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tJsGGsPNakw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Dealing with cyberbullies.</span></figcaption>
</figure>
<h2>How to handle bullies</h2>
<p>Fortunately, there are lots of ways to stop a bully.</p>
<p>If you’re a child or teenager, talk about what has happened with a trusted adult – a parent, teacher, principal or counselor. They will help you figure out your next move. Schools are familiar with this sort of problem; they have <a href="https://doi.org/10.1007/978-3-031-13134-9_3">policies in place</a> to protect victims of bullying. </p>
<p>If you’re an adult who has been bullied in the workplace, talk to your human resources department or a neutral supervisor who can advise you on next steps. You are also legally protected – employment laws <a href="https://www.eeoc.gov/harassment">prohibit harassment and discriminatory behavior</a>. </p>
<p>Whatever your age, it’s a good idea to talk to friends or family members who may not be involved in the incident but who will offer support. Engaging in coping activities – like exercising, or relaxing with a walk – <a href="https://doi.org/10.5817/CP2019-4-2">may also help</a>. </p>
<p>You can also use the <a href="https://www.crisistextline.org/topics/bullying/#bullying-and-suicide-8">Crisis Text Line</a>, available 24/7, by texting 741741. Or call the <a href="https://www.cybersmile.org/advice-help/category/who-to-call">Stop Bullying Now Hotline</a> at 1-800-273-8255; the link also provides international numbers. Or call 988 to reach the national <a href="https://988lifeline.org/">Suicide & Crisis Lifeline</a>.</p>
<p>And a final word: Bullying is not acceptable. It’s not just “kids being kids,” or that you’re “too sensitive.” If a bully is bothering you, don’t try to handle it alone – getting help is the way to get through.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/213211/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sara Goldstein does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
No matter your age, if you’re being bullied − there’s help out there.
Sara Goldstein, Professor of Human Development, University of Delaware
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/213202
2023-11-20T13:15:30Z
2023-11-20T13:15:30Z
How do crystals form?
<figure><img src="https://images.theconversation.com/files/557894/original/file-20231106-25-rk3zxx.jpg?ixlib=rb-1.1.0&rect=33%2C0%2C5595%2C3713&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Two crystalline materials together: kyanite (blue) embedded in quartz (white).</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/bladed-crystals-of-kyanite-in-quartz-from-brazil-news-photo/869774444">Photo 12/Universal Images Group via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<blockquote>
<p><strong>How do crystals form? – Alyssa Marie, age 5, New Mexico</strong></p>
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<hr>
<p>Scientifically speaking, the term “crystal” refers to any solid that has an <a href="https://theconversation.com/why-does-nature-create-patterns-a-physicist-explains-the-molecular-level-processes-behind-crystals-stripes-and-basalt-columns-186433">ordered chemical structure</a>. This means that its parts are arranged in a precisely ordered pattern, like bricks in a wall. The “bricks” can be <a href="https://australian.museum/learn/minerals/what-are-minerals/crystal-shapes/">cubes or more complex shapes</a>.</p>
<p>I’m <a href="https://scholar.google.com/citations?user=EqUjQbwAAAAJ&hl=en">an Earth scientist and a teacher</a>, so I spend a lot of time thinking about minerals. These are solid substances that <a href="https://www.britannica.com/science/mineral-chemical-compound">are found naturally in the ground</a> and can’t be broken down further into different materials other than <a href="https://www.youtube.com/watch?v=wzTRPlG1L0o">their constituent atoms</a>. Rocks are mixtures of different minerals. <a href="https://www.geologyin.com/2016/03/what-is-difference-between-minerals-and.html">All minerals are crystals</a>, but not all crystals are minerals. </p>
<p>Most rock shops sell mineral crystals that occur in nature. One is <a href="https://theconversation.com/not-so-foolish-after-all-fools-gold-contains-a-newly-discovered-type-of-real-gold-161819">pyrite, which is known as fool’s gold</a> because it looks like real gold. Some shops also feature showy, human-made crystals such as <a href="https://www.zmescience.com/feature-post/natural-sciences/geology-and-paleontology/rocks-and-minerals/the-bismuth-crystal-why-it-looks-so-amazingly-trippy-and-why-its-actually-a-big-deal-for-science/">bismuth</a>, a natural element that forms crystals when it is melted and cooled. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A dark gray rock with a large concentration of shiny yellow material covering part of its surface." src="https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=453&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=453&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=453&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=569&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=569&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557895/original/file-20231106-267473-4zr8g4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=569&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Pyrite in black shale rock from a quarry in Indianapolis, Ind.</span>
<span class="attribution"><a class="source" href="https://flic.kr/p/uJq9jj">James St. John/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<h2>Why and how crystals form</h2>
<p>Crystals grow when molecules that are alike get close to each other and stick together, forming chemical bonds that act like Velcro between atoms. Mineral crystals cannot just start forming spontaneously – they need special conditions and a <a href="https://www.thoughtco.com/definition-of-nucleation-605425">nucleation site</a> to grow on. A nucleation site can be a rough edge of rock or a speck of dust that a molecule bumps into and sticks to, starting the crystallization chain reaction.</p>
<p>At or near the Earth’s surface, many molecules are dissolved in water that flows through or over the ground. If there are enough molecules in the water that are alike, they will separate from the water as solids – a process called precipitation. If they have a nucleation site, they will stick to it and start to form crystals. </p>
<p>Rock salt, which is actually <a href="https://www.britannica.com/science/halite">a mineral called halite</a>, grows this way. So does <a href="https://www.britannica.com/science/travertine">another mineral called travertine</a>, which sometimes forms flat ledges in caves and around hot springs, where water causes chemical reactions between the rock and the air. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="White rock terraces around a vent in the earth's surface releasing steam." src="https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/557876/original/file-20231106-23-phmp31.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Travertine ledges at Mammoth Hot Springs in Yellowstone National Park in Wyoming. Terraced pools form due to deposition of travertine from the hot spring fluids as they cool and release carbon dioxide.</span>
<span class="attribution"><a class="source" href="https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/thumbnails/image/P7190038.JPG">USGS</a></span>
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<p>You can make “<a href="http://www.sciencekidsathome.com/science_experiments/growing_stalactites.html">salt stalactites</a>” at home by growing salt crystals on a string. In this experiment, the string is the nucleation site. When you dissolve Epsom salts in water and lower a string into it, then leave it for several days, the water will slowly evaporate and leave the Epsom salts behind. As that happens, salt crystals precipitate out of the water and grow crystals on the string.</p>
<p>Many places in the Earth’s crust are hot enough for <a href="https://www.britannica.com/science/magma-rock">rocks to melt into magma</a>. As that magma cools down, mineral crystals grow from it, just like water freezing into ice cubes. These mineral crystals form at much higher temperatures than salt or travertine precipitating out of water. </p>
<h2>What crystals can tell scientists</h2>
<p>Earth scientists can learn a lot from different types of crystals. For example, the presence of certain mineral crystals in rocks can reveal the rocks’ age. This dating method is called <a href="https://www.britannica.com/science/geochronology">geochronology</a> – literally, measuring the age of materials from the Earth. </p>
<p>One of the most valued mineral crystals for geochronologists is <a href="https://geology.com/minerals/zircon.shtml">zircon</a>, which is so durable that it quite literally stands the test of time. The <a href="https://www.si.edu/newsdesk/releases/earths-oldest-minerals-date-onset-plate-tectonics-36-billion-years-ago">oldest zircons ever found</a> come from Australia and are about 4.3 billion years old – almost as <a href="https://www.amnh.org/exhibitions/darwin/the-world-before-darwin/how-old-is-earth">old as our planet itself</a>. Scientists use the chemical changes recorded within zircons as they grew as a reliable “clock” to <a href="https://knowablemagazine.org/article/physical-world/2021/keeping-time-zircons">figure out how old the rocks containing them are</a>.</p>
<p>Some crystals, including zircons, have growth rings, like the <a href="https://naturalsciences.org/calendar/news/science-at-home-tree-rings/">rings of a tree</a>, that form when layers of molecules accumulate as the mineral grows. These rings can tell scientists all kinds of things about <a href="https://theconversation.com/1-000-year-old-stalagmites-from-a-cave-in-india-show-the-monsoon-isnt-so-reliable-their-rings-reveal-a-history-of-long-deadly-droughts-189222">the environment in which they grew</a>. For example, changes in pressure, temperature and magma composition can all result in growth rings.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="White rectangular feldspar crystals with faintly visible growth rings are prominent against grey granodiorite rock." src="https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=530&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=530&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=530&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=666&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=666&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559134/original/file-20231113-25-cx8jko.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=666&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Feldspar crystals with growth rings in granodiorite rock near Squamish, British Columbia.</span>
<span class="attribution"><span class="source">Natalie Bursztyn</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Sometimes mineral crystals grow as high pressure and temperatures within the Earth’s crust change rocks from one type to another in a process called <a href="https://www.amnh.org/exhibitions/permanent/planet-earth/how-do-we-read-the-rocks/three-types/metamorphic">metamorphism</a>. This process causes the elements and chemical bonds in the rock to rearrange themselves into new crystal structures. Lots of spectacular crystals grow in this way, including <a href="https://geology.com/minerals/garnet.shtml">garnet</a>, <a href="https://geology.com/minerals/kyanite.shtml">kyanite</a> and <a href="https://geology.com/minerals/staurolite.shtml">staurolite</a>.</p>
<h2>Amazing forms</h2>
<p>When a mineral precipitates from water or crystallizes from magma, the more space it has to grow, the bigger it can become. There is a <a href="https://cen.acs.org/physical-chemistry/geochemistry/Naicas-crystal-cave-captivates-chemists/97/i6">cave in Mexico full of giant gypsum crystals</a>, some of which are 40 feet (12 meters) long – the size of telephone poles.</p>
<p>Especially showy mineral crystals are also valuable as gemstones for jewelry once they are cut into new shapes and polished. The highest price ever paid for a gemstone was $71.2 million for the <a href="https://www.npr.org/sections/thetwo-way/2017/04/05/522739361/pink-star-diamond-sells-for-71-million-smashing-auction-record">CTF Pink Star diamond</a>, which went up for auction in 2017 and sold in less than five minutes.</p>
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<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/213202/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Natalie Bursztyn does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
There are a lot of myths about crystals − for example, that they are magical rocks with healing powers. An earth scientist explains some of their amazing true science.
Natalie Bursztyn, Lecturer in Geosciences, University of Montana
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/213836
2023-11-13T13:33:49Z
2023-11-13T13:33:49Z
Is time travel even possible? An astrophysicist explains the science behind the science fiction
<figure><img src="https://images.theconversation.com/files/554607/original/file-20231018-19-hyrxxn.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C960%2C540&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">If traveling into the past is possible, one way to do it might be sending people through tunnels in space.</span> <span class="attribution"><a class="source" href="https://pixabay.com/photos/astronomy-desktop-space-galaxy-3217141/">by raggio5 via Pixabay</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<blockquote>
<p><strong>Will it ever be possible for time travel to occur? – Alana C., age 12, Queens, New York</strong></p>
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<p>Have you ever dreamed of traveling through time, like characters do in science fiction movies? For centuries, the concept of time travel has captivated people’s imaginations. Time travel is the concept of moving between different points in time, just like you move between different places. In movies, you might have seen characters using special machines, magical devices or even hopping into a futuristic car to travel backward or forward in time. </p>
<p>But is this just a fun idea for movies, or could it really happen?</p>
<p>The question of whether time is reversible remains one of the biggest unresolved questions in science. If the universe follows the <a href="https://www.grc.nasa.gov/www/k-12/airplane/thermo.html">laws of thermodynamics</a>, it may not be possible. The second law of thermodynamics states that things in the universe can either remain the same or become more disordered over time. </p>
<p>It’s a bit like saying you can’t unscramble eggs once they’ve been cooked. According to this law, the universe can never go back exactly to how it was before. Time can only go forward, like a one-way street.</p>
<h2>Time is relative</h2>
<p>However, physicist Albert Einstein’s <a href="https://www.space.com/36273-theory-special-relativity.html">theory of special relativity</a> suggests that time passes at different rates for different people. Someone speeding along on a spaceship moving close to the <a href="https://www.space.com/15830-light-speed.html">speed of light</a> – 671 million miles per hour! – will experience time slower than a person on Earth. </p>
<p>People have yet to build spaceships that can move at speeds anywhere near as fast as light, but astronauts who visit the International Space Station orbit around the Earth at speeds close to 17,500 mph. Astronaut Scott Kelly has spent 520 days at the International Space Station, and as a result has aged a little more slowly than his twin brother – and fellow astronaut – Mark Kelly. Scott used to be 6 minutes younger than his twin brother. Now, because Scott was traveling so much faster than Mark and for so many days, he is <a href="https://www.space.com/33411-astronaut-scott-kelly-relativity-twin-brother-ages.html">6 minutes and 5 milliseconds younger</a>.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/yuD34tEpRFw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Time isn’t the same everywhere.</span></figcaption>
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<p>Some scientists are exploring other ideas that could theoretically allow time travel. One concept involves <a href="https://www.space.com/20881-wormholes.html">wormholes</a>, or hypothetical tunnels in space that could create shortcuts for journeys across the universe. If someone could build a wormhole and then figure out a way to move one end at close to the speed of light – like the hypothetical spaceship mentioned above – the moving end would age more slowly than the stationary end. Someone who entered the moving end and exited the wormhole through the stationary end would come out in their past. </p>
<p>However, wormholes remain theoretical: Scientists have yet to spot one. It also looks like it would be <a href="https://galileospendulum.org/2015/01/26/why-wormholes-probably-dont-exist/">incredibly challenging</a> to send humans through a wormhole space tunnel.</p>
<h2>Paradoxes and failed dinner parties</h2>
<p>There are also paradoxes associated with time travel. The famous “<a href="https://www.discovermagazine.com/the-sciences/what-is-the-grandfather-paradox-of-time-travel">grandfather paradox</a>” is a hypothetical problem that could arise if someone traveled back in time and accidentally prevented their grandparents from meeting. This would create a paradox where you were never born, which raises the question: How could you have traveled back in time in the first place? It’s a mind-boggling puzzle that adds to the mystery of time travel.</p>
<p>Famously, physicist Stephen Hawking tested the possibility of time travel by <a href="https://www.euronews.com/culture/2023/06/28/culture-re-view-the-day-stephen-hawking-threw-a-time-traveller-party">throwing a dinner party</a> where invitations noting the date, time and coordinates were not sent out until after it had happened. His hope was that his invitation would be read by someone living in the future, who had capabilities to travel back in time. But no one showed up. </p>
<p>As he <a href="https://www.penguinrandomhouse.com/books/77014/black-holes-and-baby-universes-by-stephen-hawking/">pointed out</a>: “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”</p>
<h2>Telescopes are time machines</h2>
<p>Interestingly, astrophysicists armed with powerful telescopes possess a unique form of time travel. As they peer into the vast expanse of the cosmos, they gaze into the past universe. Light from all galaxies and stars takes time to travel, and these beams of light carry information from the distant past. When astrophysicists observe a star or a galaxy through a telescope, they are not seeing it as it is in the present, but as it existed when the light began its journey to Earth millions to billions of years ago. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/QeRtcJi3V38?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Telescopes are a kind of time machine – they let you peer into the past.</span></figcaption>
</figure>
<p>NASA’s newest space telescope, the <a href="https://theconversation.com/a-cosmic-time-machine-how-the-james-webb-space-telescope-lets-us-see-the-first-galaxies-in-the-universe-187015">James Webb Space Telescope</a>, is peering at galaxies that were formed at the very beginning of the Big Bang, about 13.7 billion years ago.</p>
<p>While we aren’t likely to have time machines like the ones in movies anytime soon, scientists are actively researching and exploring new ideas. But for now, we’ll have to enjoy the idea of time travel in our favorite books, movies and dreams.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/213836/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adi Foord does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Scientists are trying to figure out if time travel is even theoretically possible. If it is, it looks like it would take a whole lot more knowledge and resources than humans have now to do it.
Adi Foord, Assistant Professor of Astronomy and Astrophysics, University of Maryland, Baltimore County
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/212949
2023-11-06T13:33:20Z
2023-11-06T13:33:20Z
Why do our noses get snotty when we are sick? A school nurse explains the powers of mucus
<figure><img src="https://images.theconversation.com/files/548367/original/file-20230914-21-s25lth.jpg?ixlib=rb-1.1.0&rect=1%2C0%2C1196%2C797&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Use a tissue and wash your hands after a booger explosion.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/schwachs/4352350750/">Joshua Wachs/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why do our noses get snotty when we are sick? – Veronica P., age 5, Panama City, Florida</strong></p>
</blockquote>
<hr>
<p>Not many things are as uncomfortable and annoying as a runny or congested nose when you’re sick. Constantly blowing your nose and not being able to breathe through it may leave you wondering: Why does this happen? </p>
<p>I’m a nurse practitioner who works with kids every day and also <a href="https://stories.purdue.edu/kristin-ahrens/">teaches nursing</a>. The answer is pretty simple. Mucus – or snot – is one of the ways your body helps keep you healthy. </p>
<p>Mucus lines your nose, throat, lungs and other parts of your body to protect it from bad bacteria, viruses and other particles. Your body <a href="https://www.everydayhealth.com/mucus/">continuously creates mucus</a> to fight off germs and help get rid of them. </p>
<p>When you’re sick, your immune system ramps up to produce extra mucus to flush out germs. While it might seem gross, mucus is also pretty amazing.</p>
<h2>Slimy protector</h2>
<p>Your body creates mucus out of a combination of <a href="https://www.britannica.com/science/mucus">water, proteins and salts</a>. Its sticky consistency traps bad microorganisms and other unwanted particles, like dust, pet dander and mildew, so they can’t get farther into your system. </p>
<p>Some components in mucus <a href="https://www.nibib.nih.gov/news-events/newsroom/disarming-bacteria-mucus-and-phages">stop bacteria from banding together</a> and becoming more dangerous. Other elements can actually <a href="https://doi.org/10.1007/BF02976990">kill the invaders</a> that are trying to make you sick. And though scientists don’t completely understand how, the <a href="https://doi.org/10.1007/BF02976990">proteins and genes in mucus</a> seem to work together to make it thicker and stickier if necessary.</p>
<p>Once germs or other potentially damaging particles are trapped and neutralized, your body’s way of getting rid of them altogether is to make so much mucus that you have to blow, sneeze or cough them out. </p>
<p>You might have noticed that sometimes when you’re sick, your nose can get red too. This is because your immune system, in addition to making mucus, also sends extra white blood cells to the source of an infection. As they rush to the scene to help fight infection, the extra white blood cells <a href="https://my.clevelandclinic.org/health/articles/21196-immune-system/">expand the blood vessels</a> in the area, making your nose look red. All the wiping and blowing can make it red, too.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/548373/original/file-20230914-9125-jab4s8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart displaying mucus colors from clear to black and describing what each means." src="https://images.theconversation.com/files/548373/original/file-20230914-9125-jab4s8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548373/original/file-20230914-9125-jab4s8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=960&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548373/original/file-20230914-9125-jab4s8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=960&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548373/original/file-20230914-9125-jab4s8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=960&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548373/original/file-20230914-9125-jab4s8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1206&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548373/original/file-20230914-9125-jab4s8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1206&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548373/original/file-20230914-9125-jab4s8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1206&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The mucus rainbow.</span>
<span class="attribution"><a class="source" href="https://riseandshine.childrensnational.org/snot-colors-and-what-they-mean/">Children's National Hospital</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<p>Snot can come in a rainbow of yucky colors. When white blood cells are fighting an infection, they release chemicals that may <a href="https://www.healthline.com/health/snot-color#white-snot">turn your snot yellow</a>. When more of those cells are needed to get the job done, mucus can even turn green. Typically, after a few days, colored mucus changes back to clear and your stuffy nose will go away. </p>
<h2>Not just in your nose</h2>
<p>Mucus isn’t found just in your nose and lungs.</p>
<p>Your <a href="https://theconversation.com/can-you-cry-underwater-205464">eyes also have a thin layer of mucus</a> that helps protect them from particles in the air. When you get sick or get an eye infection, <a href="https://www.verywellhealth.com/eye-mucus-types-3422108">eye mucus</a> can act the same way it does in your nose – catching and killing germs. Eye mucus can also sometimes turn thick and yellow. If that happens, you’ll want to call your health care provider. Don’t ever touch your eyes with your fingers. That can <a href="https://www.nyoph.com/blog/this-is-why-you-shouldnt-rub-your-eyes/">introduce more germs</a>.</p>
<p>Your stomach and intestines also have protective mucus. If you’ve ever had an upset stomach that led to diarrhea, the mucus in your intestinal track was working overtime to help <a href="https://doi.org/10.1038/nrgastro.2013.35">flush out bad bacteria</a>. That’s why your normal poop goes from a solid mush to something more slimy. There are other reasons you can have stomachaches – like stress, constipation or food allergies – but if you have diarrhea, your mucus is definitely hard at work. </p>
<h2>Animals have it too</h2>
<p>Humans aren’t the only animals that use mucus. For example, <a href="https://petriage.com/clinical-insights/your-pets-mucous-membranes/">dogs and cats have mucus</a> too.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/548831/original/file-20230918-31-zzsqlo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A brightly colored fish is surrounded by a mucus cocoon on the sea floor next to some rocks. A smaller fish is nearby." src="https://images.theconversation.com/files/548831/original/file-20230918-31-zzsqlo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548831/original/file-20230918-31-zzsqlo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548831/original/file-20230918-31-zzsqlo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548831/original/file-20230918-31-zzsqlo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548831/original/file-20230918-31-zzsqlo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548831/original/file-20230918-31-zzsqlo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548831/original/file-20230918-31-zzsqlo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Some fish use mucus for protection while sleeping.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Abrolhos_Marine_National_ParkRobertoCostaPinto20.jpg">RobertoCostaPinto/WikiMedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p><a href="https://www.montereybayaquarium.org/stories/mucus-slime-snot">Parrotfish</a>, <a href="https://doi.org/10.1098/rsbl.2010.0916">wrasses</a> and <a href="https://cimi.org/blog/mucus-in-the-animal-kingdom/">other sea creatures</a> produce mucus cocoons to help protect them from predators at night. </p>
<p>Chameleons use the sticky <a href="https://www.nationalgeographic.com/animals/article/chameleon-tongue-mucus-sticky-animals">mucus on the end of their tongues</a> to reel in their prey. Earthworms secrete mucus to help them move through the soil, which in turn <a href="https://doi.org/10.5194/egusphere-egu2020-17611">benefits the soil</a>.</p>
<p>In humans, mucus helps neutralize and eliminate the microbial bad guys. So the next time you reach for a tissue to blow your nose, remember: Your body’s natural defenses are doing their best to keep you healthy or make you better. Just think of all that snot as one of your body’s superpowers.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/212949/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kristin Ahrens is a member of the National Association of Pediatric Nurse Practitioners (NAPNAP) and the National Association of School Nurses (NASN). </span></em></p>
Slimy snot is an important part of how your immune system wards off germs and fights back from infection.
Kristin Ahrens, Pediatric Nurse Practitioner, Adjunct Instructor of Nursing at Purdue Global, Purdue University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/210048
2023-10-24T13:26:36Z
2023-10-24T13:26:36Z
Are ghosts real? A social psychologist examines the evidence
<figure><img src="https://images.theconversation.com/files/543535/original/file-20230818-4259-hhjv4b.jpg?ixlib=rb-1.1.0&rect=8%2C16%2C5540%2C3676&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Remember the old saying: Extraordinary claims require extraordinary evidence.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/looking-up-at-a-spooky-blurred-ghostly-figure-royalty-free-image/1266059277?phrase=Ghosts&adppopup=true">David Wall/Moment via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Is it possible for there to be ghosts? – Madelyn, age 11, Fort Lupton, Colorado</strong></p>
</blockquote>
<hr>
<p>Certainly, lots of people believe in ghosts – a spirit left behind after someone who was alive has died.</p>
<p>In a 2021 <a href="https://today.yougov.com/topics/entertainment/articles-reports/2021/10/21/americans-say-ghosts-exist-seen-a-ghost">poll of 1,000 American adults</a>, 41% said they believe in ghosts, and 20% said they had personally experienced them. If they’re right, that’s more than 50 million spirit encounters in the U.S. alone.</p>
<p>That includes the owner of a retail shop near my home who believes his place is haunted. When I asked what most convinced him of this, he sent me dozens of eerie security camera video clips. He also brought in ghost hunters who reinforced his suspicions. </p>
<p>Some of the videos show small orbs of light gliding around the room. In others, you can hear faint voices and loud bumping sounds when nobody’s there. Others show a <a href="https://youtube.com/clip/UgkxUDWmE2OLTCMcgoRoApiRZs9at_eJQZjj">book flying off a desk</a> and products jumping off a shelf. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/MyQT78Bjt04?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Many ghostly encounters are due to the way your brain interprets certain sights and sounds.</span></figcaption>
</figure>
<p>It’s not uncommon for me to hear stories like this. <a href="https://scholar.google.com/citations?user=ZEQu09wAAAAJ&hl=en">As a sociologist</a>, some of my work looks at beliefs in things like <a href="https://www.postandcourier.com/news/scared-of-ghosts-thats-because-you-want-to-be-sc-researchers-say/article_b87cf418-f735-11e9-bdb4-1bab7238a47f.html">ghosts</a>, <a href="https://theconversation.com/why-people-tend-to-believe-ufos-are-extraterrestrial-208403">aliens</a>, <a href="https://journals.sagepub.com/doi/abs/10.1525/sop.2001.44.1.21">pyramid power</a> and <a href="https://theconversation.com/why-is-13-considered-unlucky-explaining-the-power-of-its-bad-reputation-191477">superstitions</a>. </p>
<p>Along with others who practice scientific skepticism, I keep an open mind while maintaining that extraordinary claims require extraordinary evidence. Tell me you had a burger for lunch, and I’ll take your word for it. Tell me you shared your fries with Abraham Lincoln’s ghost, and I’ll want more evidence.</p>
<p>In the “spirit” of critical thinking, consider the following three questions:</p>
<h2>Are ghosts possible?</h2>
<p>People may think they’re experiencing ghosts when they hear strange voices, see moving objects, witness balls or wisps of light or even translucent people. </p>
<p>Yet no one describes ghosts as <a href="https://www.britannica.com/topic/ghost-spirit">aging, eating, breathing</a> or using bathrooms – despite plumbers receiving many calls about toilets “<a href="https://www.theplumberguy.com/blog/what-to-do-when-your-toilet-ghost-flushes/">ghost-flushing</a>.” </p>
<p>So could ghosts be made of a <a href="https://www.livescience.com/16951-einstein-physics-ghosts-proof.html">special kind of energy</a> that hovers and flies without dissipating? </p>
<p>If that’s the case, that means when ghosts glow, move objects and make sounds, they are acting like matter – something that takes up space and has mass, like wood, water, plants and people. Conversely, when passing through walls or vanishing, they must not act like matter. </p>
<p>But centuries of <a href="https://www.eia.gov/energyexplained/what-is-energy/forms-of-energy.php">physics research</a> have found nothing like this exists, which is why physicists say <a href="https://futurism.com/brian-cox-if-ghosts-existed-wed-have-found-evidence-for-them-by-now">ghosts can’t exist</a>. </p>
<p>And so far, there is no proof that any part of a person can continue on after death. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/v-WPEeZW8i0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The real truth is out there, says this ghost skeptic.</span></figcaption>
</figure>
<h2>What’s the evidence?</h2>
<p>Never before in history have people recorded so many ghost encounters, thanks in part to mobile phone cameras and microphones. It seems there would be great evidence by now. <a href="https://benjaminradford.com/investigating-ghosts-2/">But scientists don’t have it</a>. </p>
<p>Instead, there are lots of ambiguous recordings sabotaged by bad lighting and faulty equipment. But popular <a href="https://www.eonline.com/news/1306826/ranking-ghost-hunting-shows-from-ghoulish-to-down-right-silly">television shows on ghost hunting</a> convince many viewers that blurry images and emotional reactions are proof enough. </p>
<p>As for <a href="https://www.ghoststop.com/tough-ghost-hunting-kit/">all the devices</a> ghost hunters use to capture sounds, electrical fields and infrared radiation – they may look scientific, but <a href="https://skepticalinquirer.org/exclusive/reality-check-ghost-hunters-and-lsquoghost-detectorsrsquo/">they’re not</a>. Measurements are worthless without some knowledge of the thing you’re measuring.</p>
<p>When ghost hunters descend on an allegedly haunted location for a night of meandering and measurement, they usually find something they later deem paranormal. It may be a moving door (breeze?), a chill (gap in the floorboards?), a glow (light entering from outside?), electrical fluctuations (old wiring?), or bumps and faint voices (crew in other rooms?). </p>
<p>Whatever happens, ghost hunters will draw a bull’s-eye around it, interpret that as “evidence” <a href="https://www.newsweek.com/ghost-hunters-who-use-science-reveal-what-other-paranormal-investigators-get-wrong-1642693">and investigate no further</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/XqH8t-N1aTo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">There’s a scientific explanation for spooky sightings.</span></figcaption>
</figure>
<h2>Are there alternative explanations?</h2>
<p>Personal experiences with ghosts can be misleading due to the limitations of human senses. That’s why anecdotes can’t substitute for objective research. Alleged hauntings usually have plenty of non-ghostly explanations.</p>
<p>One example is that retail establishment in my neighborhood. I reviewed the security camera clips and gathered information about the store’s location and layout, and the exact equipment used in the recordings. </p>
<p>First, the “orbs”: Videos captured many small globes of light seemingly moving around the room. </p>
<p>In reality, the orbs are <a href="https://support.simplisafe.com/articles/video-doorbell-pro/why-do-i-see-orbsbubbles-when-my-camera-is-in-night-mode/634492a5d9a8b404da76cccb">tiny particles of dust</a> wafting close to the camera lens, made to “bloom” by the camera’s infrared lights. That they appear to float around the room is an optical illusion. Watch any orb video closely and you’ll see they never go behind objects in the room. That’s exactly what you’d expect with dust particles close to the camera lens.</p>
<p>Next, voices and bumps: The shop is in a busy corner mini-mall. Three walls abut sidewalks, loading zones and parking areas; an adjacent store shares the fourth. The security camera mics probably recorded sounds from outdoors, other rooms and the adjacent unit. The owner never checked for these possibilities.</p>
<p>Then, the flying objects: The video shows objects falling off the showroom wall. The shelf rests on adjustable brackets, one of which wasn’t fully seated in its slot. The weight of the shelf caused the bracket to settle into place with a visible jerk. This movement sent some items tumbling off the shelf.</p>
<p>Then, the flying book: I used a simple trick to <a href="https://www.youtube.com/watch?v=soA5P1myQ7k&ab_channel=BarryMarkovsky">recreate the event</a> at home: a hidden string taped inside a book’s cover, wrapped around the kitchen island, and tugged by my right hand out of camera range. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/soA5P1myQ7k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Experience the mystery of the flying book.</span></figcaption>
</figure>
<p>Now I can’t prove there wasn’t a ghost in the original video.
The point is to provide a more plausible explanation than “it must have been a ghost.” </p>
<p>One final consideration: Virtually all ghostly experiences involve impediments to making accurate perceptions and judgments – <a href="https://skepticalinquirer.org/2017/01/ghost-hunters-in-the-dark/">bad lighting</a>, <a href="https://doi.org/10.3389/fpsyg.2022.879163">emotional arousal</a>, <a href="https://time.com/6259846/sleep-paralysis-ghosts/">sleep phenomena</a>, <a href="https://journals.sagepub.com/doi/abs/10.1525/sop.2001.44.1.21">social influences</a>, <a href="https://www.livescience.com/21478-what-is-culture-definition-of-culture.html">culture</a>, a misunderstanding of <a href="https://skepticalinquirer.org/exclusive/ghost-meters-i-can-name-that-ghost-in-5-milligauss/">how recording devices work</a>, and <a href="https://news.mit.edu/2019/how-expectation-influences-perception-0715">the prior beliefs</a> and <a href="https://doi.org/10.1007/s12144-018-0047-9">personality traits</a> of those who claim to see ghosts. All of these hold the potential to induce unforgettable ghostly encounters.</p>
<p>But all can be explained without ghosts being real.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/210048/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Barry Markovsky does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Ghosts can be spooky fun, but there’s no evidence they exist.
Barry Markovsky, Distinguished Professor Emeritus of Sociology, University of South Carolina
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/210118
2023-10-23T12:24:57Z
2023-10-23T12:24:57Z
How much time do kids spend on devices – playing games, watching videos, texting and using the phone?
<figure><img src="https://images.theconversation.com/files/544091/original/file-20230822-5267-868e99.jpg?ixlib=rb-1.1.0&rect=10%2C10%2C6699%2C4456&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Today, nearly all U.S. teens have a smartphone.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/teenage-boy-using-smartphone-at-home-royalty-free-image/1218225082?phrase=teen+on+social+media+looking+unhappy&adppopup=true">MoMo Productions/Digital Vision via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
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</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>How many hours does the average American spend on devices each year? – Maxwell P., age 10</strong></p>
</blockquote>
<hr>
<p>Think about your favorite devices – your smartphone, laptop, tablet, computer or console – the things you use to play cool games, watch hilarious videos and connect and chat with friends. </p>
<p>Many young people spend a lot of free time looking at them. Turns out that teens spend an average of <a href="https://www.commonsensemedia.org/research/the-common-sense-census-media-use-by-tweens-and-teens-2021">8½ hours on screens per day</a>, and tweens – that’s ages 8 to 12 – are not far behind, at 5½ hours daily.</p>
<p>Keep in mind those numbers are for only social media, gaming and texting. They do not include the time that kids <a href="https://www.apa.org/monitor/2020/04/cover-kids-screens">used screens for schoolwork or homework</a>.</p>
<p>What’s more, much of the time taken up by social media and texting is apparently not even enjoyable, much less productive. A 2017 study of teens ages 13 to 18 suggests they spend most of those hours on the phone <a href="https://www.theatlantic.com/magazine/archive/2017/09/has-the-smartphone-destroyed-a-generation/534198/">in their bedroom, alone and distressed</a>. </p>
<p>These lonely feelings correlate with the <a href="https://doi.org/10.1177/0265407519836170">rise in the use of digital media</a>. In 2022, <a href="https://www.pewresearch.org/internet/2022/08/10/teens-social-media-and-technology-2022/">95% of teens had smartphones</a> compared with only 23% in 2011. And 46% of today’s teens say they use the internet almost constantly, compared with 24% of teenagers who said the same in 2014 and 2015. </p>
<p><a href="https://www.med.wayne.edu/profile/aa3409">Our team of psychiatrists</a> who treat young people with digital addiction have many patients who spend over 40 hours per week on screens – and some, up to 80 hours. </p>
<p>Think about it: If you spend “just” an average of 50 hours per week on devices from ages 13 to 18 – the total time you will spend on screens equates to more than 12 years of school!</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Wl-TJyPKu_s?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The U.S. surgeon general says too much screen time can increase anxiety and depression in teens and tweens.</span></figcaption>
</figure>
<h2>Find the right balance</h2>
<p>All this is not to say that everything about devices is bad. In this digital age, people embark on exciting journeys through the screens of their devices. Sometimes, screens are the windows to a magical adventure. </p>
<p>But too much screen time can lead to problems. As human beings, we function best when we’re in a state of balance. That happens when we eat well, exercise regularly and get enough sleep.</p>
<p>But spending too much time using digital devices can cause changes in the way you think and behave. Many teens and tweens developed the “fear of missing out” – <a href="https://saferkidsonline.eset.com/sg/article/5-tips-for-combating-fomo">known as FOMO</a>. And one study shows <a href="https://doi.org/10.3390/ijerph17020580">some people develop nomophobia</a>, which is the fear of being without your phone, or feeling anxious when you can’t use it. </p>
<p>Moreover, digital addiction in high school may predict serious <a href="https://doi.org/10.3390/children10010086">depression, anxiety and sleep disruption</a> in college. </p>
<p>Rates of depression and anxiety <a href="https://doi.org/10.1016/j.jpsychires.2012.11.015">are skyrocketing among college students</a>. The fear of missing out is pervasive, resulting in sleep disruption; too many college students <a href="https://doi.org/10.3390/ijerph19159693">sleep with smartphones turned on</a> and near their bed – and wake up to respond to texts and notifications during the night. Sleep disruption itself is a core symptom of <a href="https://doi.org/10.31887/DCNS.2008.10.3/dnutt">both depression and anxiety</a>. </p>
<h2>How to avoid device addiction</h2>
<p>A 2016 poll indicated that half of teens felt they were <a href="https://www.commonsensemedia.org/press-releases/new-report-finds-teens-feel-addicted-to-their-phones-causing-tension-at-home">addicted to their mobile devices</a>. </p>
<p>Getting hooked on screens means missing out on healthy activities. To achieve a better balance, <a href="https://www.aacap.org/AACAP/Families_and_Youth/Facts_for_Families/FFF-Guide/Children-And-Watching-TV-054.aspx">some experts recommend the following</a>: Turn off all screens during family meals and outings. Don’t complain when your parents use parental controls. And turn off all the screens in your bedroom 30 to 60 minutes before bedtime – this step will improve sleep. </p>
<p>You may be a “<a href="https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/are-video-games-and-screens-another-addiction#:%7E">screen addict</a>” if you: </p>
<ul>
<li>Feel uneasy or grumpy when you can’t use your device.</li>
<li>Don’t take breaks while spending hours on your device.</li>
<li>Ignore other fun activities you enjoy, like going outside or reading a book.</li>
<li>Have trouble sleeping, or falling asleep, because your screen time is too close to bedtime.</li>
<li>Experience eye, lower back and neck strain.</li>
<li>Struggle with weight gain or obesity because you’re inactive.</li>
<li>Have difficulty with real-life, face-to-face social interactions.</li>
</ul>
<p>If you notice these signs, do not dismiss them. But also realize you’re not alone and help is out there. You can find balance again.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/8e1ezeq3C9c?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A kid breaks his addiction to gaming and social media.</span></figcaption>
</figure>
<h2>A healthy approach</h2>
<p>Exercise – riding a bike, playing sports, lifting weights or going for a jog or walk – <a href="https://theconversation.com/the-exercise-pill-how-exercise-keeps-your-brain-healthy-%20and-protects-it-against-depression-and-anxiety-155848">keeps your brain healthy</a> and protects it against depression and anxiety, as well as limiting your screen time.</p>
<p>Another way to be happier and healthier is to spend time with people – face to face, not via a screen. Seeing people live and in person is the <a href="https://news.harvard.edu/gazette/story/2017/04/over-nearly-80-years-harvard-study-has-been-showing-how-to-live-a-healthy-and-happy-life/">best way to bond with others</a>, and it may be even better for life span than exercise. </p>
<p>Creative hobbies are good, too. Cooking, playing an instrument, dancing, any arts and crafts, and thousands of other fun things make people happier and more creative. What’s more, hobbies make you well rounded <a href="https://fordhamram.com/2023/04/19/learn-how-to-meet-people-with-social-hobbies#:%7E">and more attractive to others</a> – which leads to more face-to-face interactions. </p>
<p>It’s also critical for parents to practice healthy screen habits. But about one-third of adults <a href="https://www.pewresearch.org/short-reads/2021/03/26/about-three-in-ten-u-s-adults-say-they-are-almost-constantly-online/">say they use screens “constantly</a>.” This is not exactly a great example for kids; when adults take responsibility to minimize their own screen time, the whole family gets better.</p>
<p>Our research team used magnetic resonance imaging, <a href="https://kidshealth.org/en/parents/mri.html#:%7E">also known as MRI</a>, to scan the brains of teens who had digital addiction. We found impairment in the brain’s decision-making, processing and reward centers. But after a digital fast – meaning the addicted teens unplugged for two weeks – those brain abnormalities reversed, and the damage was undone. </p>
<p>Our findings also showed that kids with a desire to overcome digital addiction did better with a digital fast than those who were less willing or who denied their addiction. </p>
<p>A balanced lifestyle in the digital age is all about finding joy in screenless activities – being active, connecting with others and exploring your offline interests.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/210118/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rosenberg receives funding from the Children’s Hospital of Michigan Foundation, Detroit, MI, and a grant from the National Institute of Mental Health (R01MH59299). This work was also supported in part by the State of Michigan Lycaki Young Fund and the Detroit Wayne Integrated Health Network.</span></em></p><p class="fine-print"><em><span>Natalia Szura does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Up to 50% of US teens feel they are addicted to their devices. But help is out there.
David Rosenberg, Professor of Psychiatry and Neuroscience, Wayne State University
Natalia Szura, Research Assistant in Psychiatry, Wayne State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/205810
2023-10-16T12:30:12Z
2023-10-16T12:30:12Z
Why is space so dark even though the universe is filled with stars?
<figure><img src="https://images.theconversation.com/files/538108/original/file-20230718-17-5jcl17.jpg?ixlib=rb-1.1.0&rect=26%2C6%2C996%2C676&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This age old question has been dubbed Olbers' paradox.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-milky-way-appears-over-the-valle-de-la-luna-in-the-news-photo/1418507439?adppopup=true">John Moore via Getty Images News</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why is space so dark despite all of the stars in the universe? – Nikhil, age 15, New Delhi</strong></p>
</blockquote>
<hr>
<p>People have been asking why space is dark despite being filled with stars for so long that this question has a special name – <a href="https://lambda.gsfc.nasa.gov/product/suborbit/POLAR/cmb.physics.wisc.edu/tutorial/olbers.html">Olbers’ paradox</a>.</p>
<p>Astronomers estimate that there are about <a href="https://theconversation.com/how-many-stars-are-there-in-space-165370">200 billion trillion stars</a> in the observable universe. And many of those stars are as bright or even brighter than our sun. So, why isn’t space filled with dazzling light?</p>
<p><a href="http://www.astrojack.com/">I am an astronomer</a> who studies stars and planets – including those outside our solar system – and their motion in space. The study of distant stars and planets helps <a href="https://scholar.google.com/citations?user=pF3HbeQAAAAJ&hl=en&oi=ao">astronomers like me</a> understand why space is so dark.</p>
<hr>
<iframe id="noa-web-audio-player" style="border: none" src="https://embed-player.newsoveraudio.com/v4?key=x84olp&id=https://theconversation.com/why-is-space-so-dark-even-though-the-universe-is-filled-with-stars-205810&bgColor=F5F5F5&color=D8352A&playColor=D8352A" width="100%" height="110px"></iframe>
<p><em>You can listen to more articles from The Conversation, narrated by Noa, <a href="https://theconversation.com/us/topics/audio-narrated-99682">here</a>.</em></p>
<hr>
<p>You might guess it’s because a lot of the stars in the universe are very far away from Earth. Of course, it is true that the farther away a star is, the less bright it looks – <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/isq.html">a star 10 times farther away looks 100 times dimmer</a>. But it turns out this isn’t the whole answer. </p>
<h2>Imagine a bubble</h2>
<p>Pretend, for a moment, that the universe is so old that the light from even the farthest stars has had time to reach Earth. In this imaginary scenario, all of the stars in the universe are not moving at all.</p>
<p>Picture a large bubble with Earth at the center. If the bubble were about 10 <a href="https://exoplanets.nasa.gov/faq/26/what-is-a-light-year/">light years</a> across, it would contain about <a href="https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs">a dozen stars</a>. Of course, at several light years away, many of those stars would look pretty dim from Earth. </p>
<p>If you keep enlarging the bubble to 1,000 light years across, then to 1 million light years, and then 1 billion light years, the farthest stars in the bubble will look even more faint. But there would also be more and more stars inside the bigger and bigger bubble, all of them contributing light. Even though the farthest stars look dimmer and dimmer, there would be a lot more of them, and the whole night sky should look very bright.</p>
<p>It seems I’m back where I started, but I’m actually a little closer to the answer.</p>
<h2>Age matters</h2>
<p>In the imaginary bubble illustration, I asked you to imagine that the stars are not moving and that the universe is very old. But the universe is only about <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question28.html">13 billion years old</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Image of lightly colored galaxies and stars against dark background" src="https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=613&fit=crop&dpr=1 600w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=613&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=613&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=770&fit=crop&dpr=1 754w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=770&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/538112/original/file-20230718-39873-q38o2g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=770&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Galaxies as they appeared approximately 13.1 billion years ago, taken by the James Webb Space Telescope.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/image-released-by-nasa-on-july-11-2022-shows-galaxy-cluster-news-photo/1241872380?adppopup=true">NASA/ESA/CSA/STScI/Handout from Xinhua News Agency via Getty Images</a></span>
</figcaption>
</figure>
<p>Even though that’s an amazingly long time in human terms, it’s short in astronomical terms. It’s short enough that the light from stars more distant than about 13 billion light years hasn’t actually reached Earth yet. And so the actual bubble around Earth that contains all the stars we can see only extends out to about <a href="https://science.nasa.gov/observable-universe">13 billion light years from Earth</a>.</p>
<p>There just are not enough stars in the bubble to fill every line of sight. Of course, if you look in some directions in the sky, you can see stars. If you look at other bits of the sky, you can’t see any stars. And that’s because, in those dark spots, the stars that could block your line of sight are so far away their light hasn’t reached Earth yet. As time passes, light from these more and more distant stars will have time to reach us. </p>
<h2>The Doppler shift</h2>
<p>You might ask whether the night sky will eventually light up completely. But that brings me back to the other thing I told you to imagine: that all of the stars are not moving. The universe is actually expanding, with the most distant galaxies <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/redshift.html">moving away from Earth at nearly the speed of light</a>. </p>
<p>Because the galaxies are moving away so fast, the light from their stars is pushed into colors the human eye can’t see. This effect is called the <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/redshift.html">Doppler shift</a>. So, even if it had enough time to reach you, <a href="https://svs.gsfc.nasa.gov/12856">you still couldn’t see</a> the light from the most distant stars with your eyes. And the night sky would not be completely lit up. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ikgRZt1BSyk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Doppler shift, also known as the redshift, is a phenomenon in which light from objects that are moving away from an observer appears more toward the red end of the spectrum.</span></figcaption>
</figure>
<p>If you wait even longer, eventually the stars will all burn out – <a href="https://astronomy.swin.edu.au/cosmos/m/main+sequence+lifetime">stars like the sun last only about 10 billion years</a>. Astronomers hypothesize that in the distant future – a thousand trillion years from now – the universe will go dark, <a href="https://en.wikipedia.org/wiki/The_Five_Ages_of_the_Universe">inhabited by only stellar remnants</a> like white dwarfs and black holes.</p>
<p>Even though our night sky isn’t completely filled with stars, we live in a very special time in the universe’s life, when we’re lucky enough to enjoy a rich and complex night sky, filled with light and dark.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/205810/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brian Jackson receives federally funded research grants from NASA. </span></em></p>
An astronomer explains why space looks so dark despite containing 200 billion trillion stars.
Brian Jackson, Associate Professor of Astronomy, Boise State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/204591
2023-10-09T12:20:15Z
2023-10-09T12:20:15Z
Are people born with good balance? A physical therapist explains the systems that help keep you on your toes
<figure><img src="https://images.theconversation.com/files/534129/original/file-20230626-17-igy6uh.jpg?ixlib=rb-1.1.0&rect=53%2C26%2C5919%2C3952&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">People learn balance as they grow – and can usually improve their balance with practice.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/young-woman-riding-on-the-skateboard-on-the-road-royalty-free-image/1415025581?adppopup=true">uzhursky/iStock via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Are people born with good balance? – Sebastian L., age 15, Skanderborg, Denmark</strong></p>
</blockquote>
<hr>
<p>No one is born with the ability to ride a skateboard, surf or even stand on their tiptoes. Unlike other mammals, human beings have no balance at birth – virtually no capacity to walk or even stand. Before that can happen, their vision, hearing, muscles, bones and brain must develop. This takes months, and <a href="https://www.ncbi.nlm.nih.gov/books/NBK557518/">for some activities, even years</a>. </p>
<p>Infants typically begin rolling over when they’re 6 months old. They generally start to crawl by 9 months, and stand around a year old. By 18 months old, most can walk alone and go up steps. By age 2, toddlers can perform more complex tasks, such as <a href="https://www.ncbi.nlm.nih.gov/books/NBK557518/">kicking a ball</a>. By 3 years old, most children run well and can walk up and down stairs with one foot on each stair. Some children reach these milestones faster, and some are slower, and that’s normal.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/oFl3nkghbHE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">It’s all about practice, practice, practice.</span></figcaption>
</figure>
<h2>Balance is a skill</h2>
<p>As you get older, you may notice that some people are really good at keeping their balance. They can dance well, jump rope and do somersaults. But they were not born with this ability. Instead, it took practice. Balance is a skill – the more you practice any skill, the better you become, though some people may be more naturally adept at it.</p>
<p><a href="https://www.binghamton.edu/decker/about/profile.html?id=gsingh">As a physical therapist</a> for over 15 years, I’ve seen patients of all ages who struggle with balance, and I’ve learned that it takes three of the body’s systems working together to keep a person in good balance: <a href="https://theconversation.com/development-of-vision-in-early-childhood-no-screens-before-age-two-193192">the visual</a>, <a href="https://www.physio-pedia.com/Somatosensation">somatosensory</a> and <a href="https://www.physio-pedia.com/Vestibular_System">vestibular systems</a>. </p>
<p>The visual system includes the eyes, the optic nerves that connect the eyes to the brain, and the brain’s visual cortex. Babies are born nearsighted, able to see only about 10 to 12 inches away. <a href="https://www.aao.org/eye-health/tips-prevention/baby-vision-development-first-year">As their visual system develops</a>, their brain learns how to process visual information, so they get better at moving and balancing. </p>
<p>The somatosensory system registers sensations detected by the muscles, joints, skin and the body tissues that connect them, <a href="https://my.clevelandclinic.org/health/body/23251-fascia">called the fascia</a>. These perceptions of touch, pressure, pain, temperature, position, movement and vibration travel via pathways in the spinal cord, brain stem and thalamus – a small, egg-shaped structure in the middle of the human brain – where they are integrated and analyzed. </p>
<p>For example, <a href="https://theconversation.com/infants-need-lots-of-active-movement-and-play-and-there-are-simple-ways-to-help-them-get-it-173975">when a baby tries to stand</a>, their brain processes the feelings coming from their feet, legs and hands to help them balance.</p>
<p>The vestibular system, which is the body’s system of hearing as well as balance, consists of five distinct organs in the ear. Inside these organs there is fluid, which moves when the body and head move. As this fluid moves, it sends signals to the brain, which in turn makes a person aware of their position and helps them balance.</p>
<p>The central nervous system uses the information coming from these three systems <a href="https://www.physio-pedia.com/The_Postural_Control_System?">and generates signals</a> that are sent back to appropriate muscles in the body <a href="https://www.researchgate.net/figure/The-Balance-System-Balance-as-a-function-of-vestibular-system-with-visual-and-sensory_fig1_330853004">to help maintain good balance</a>. </p>
<p>Healthy individuals rely roughly 70% on somatosensory information, 20% on vestibular system information and 10% on vision to maintain balance on firm surfaces. </p>
<p>Abnormality in any one of these three systems may result in balance problems. But when one system is affected, the other two can be trained to compensate. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/JgwZ2jZ1fSc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Ananth Vijendren, a physical therapist, explains how he assesses patients who see him for balance problems.</span></figcaption>
</figure>
<h2>Becoming unbalanced</h2>
<p>There are many ways to lose one’s balance. Standing on slippery ice, the sensory receptors in the feet are <a href="https://doi.org/10.1080/19424280.2015.1031193">unable to send appropriate signals</a> to the brain quickly enough for the brain to activate muscles to maintain balance. </p>
<p>For many people, walking in the dark means risking a fall because the brain is receiving so little visual information about the environment. People with poor or no eyesight learn to <a href="https://www.smithsonianmag.com/smart-news/blind-peoples-brains-rewire-themselves-enhance-other-senses-180962653/">rely more on the other two sensory systems</a> to maintain balance. </p>
<p>When something knocks a person off balance, such as being bumped while walking or running, it can cause something called a “vestibulospinal reflex.” The vestibular and somatosensory systems <a href="https://www.physio-pedia.com/Vestibular_Anatomy_and_Neurophysiology?">send signals to the brain</a>, which in turn activate the appropriate muscles to save the person from falling.</p>
<p>As people get older, <a href="https://theconversation.com/balance-declines-with-age-but-exercise-can-help-stave-off-some-of-the-risk-of-falling-204174">their balance often declines</a> due to age-related changes to their muscle strength and vision, as well as other causes. This increases their risk of falling. In fact, falls are a <a href="https://www.cdc.gov/falls/data/index.html#">leading cause of physical injuries</a> for adults 65 years and older. Older adults can work on balance, strength and flexibility exercises as a <a href="https://www.hjphysicaltherapy.com/strengthen-your-balance/#">way to prevent falls</a>.</p>
<p>People can also have trouble with balance due to neurological problems, <a href="https://health.clevelandclinic.org/osteoarthritis-in-your-hips-or-knees-try-this-to-improve-your-balance-and-avoid-falls/#">arthritis and joint injuries</a>.</p>
<figure class="align-center ">
<img alt="Woman gymnast balancing on one bent leg on a balance beam with the other leg extended straight behind her." src="https://images.theconversation.com/files/537368/original/file-20230713-25-hc5vek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537368/original/file-20230713-25-hc5vek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537368/original/file-20230713-25-hc5vek.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537368/original/file-20230713-25-hc5vek.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537368/original/file-20230713-25-hc5vek.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537368/original/file-20230713-25-hc5vek.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537368/original/file-20230713-25-hc5vek.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Gymnast Misaki Masui of Japan demonstrated her athletic skills on the balance beam during a June 2023 national competition in Tokyo.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/misaki-masui-competes-in-the-womens-balance-beam-final-on-news-photo/1258615102?adppopup=true">Kiyoshi Ota/Getty Images AsiaPac via Getty Images</a></span>
</figcaption>
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<h2>Learning better balance</h2>
<p>All of this explains why it’s necessary to practice if you want to improve your balance. For example, gymnasts who <a href="https://doi.org/10.1007/s40279-016-0631-9">practice walking on narrow beams</a> continuously challenge their somatosensory and vestibular systems. This trains their brains to respond to very subtle changes, which means they get better and better at staying on their toes.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-olympic-gymnasts-can-teach-us-about-improving-our-balance-165171">What Olympic gymnasts can teach us about improving our balance</a>
</strong>
</em>
</p>
<hr>
<p>.</p>
<p>People are sometimes born with disorders or developmental problems, <a href="https://www.cdc.gov/ncbddd/cp/facts.html#">such as cerebral palsy</a>, that affect the visual, vestibular or somatosensory systems. Infants with such issues ideally start physical therapy very early, which allows them to achieve developmental milestones – from holding their heads up to standing and moving independently.</p>
<p>When I treat people with balance problems, I begin by evaluating whether their somatosensory system is working properly, and I ask about injuries to muscles or bones. Depending on what the problem is, we may do simple exercises such as standing or marching in one place, and progress to more difficult exercises such as walking fast or walking while talking.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/204591/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gurpreet Singh does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
Balancing well is a whole-body experience that develops over time and takes practice to master.
Gurpreet Singh, Assistant Professor of Physical Therapy, Binghamton University, State University of New York
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/205809
2023-10-02T12:29:02Z
2023-10-02T12:29:02Z
How do astronomers know the age of the planets and stars?
<figure><img src="https://images.theconversation.com/files/529821/original/file-20230602-6875-7ttf8v.jpg?ixlib=rb-1.1.0&rect=1%2C16%2C1005%2C671&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Astronomers can estimate ages for stars outside the Solar System, but not planets.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-constellation-sagittarius-taken-from-the-u-s-naval-news-photo/615295876?adppopup=true">Corbis Historical via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>How do we know the age of the planets and stars? – Swara D., age 13, Thane, India</strong></p>
</blockquote>
<hr>
<p>Measuring the ages of planets and stars helps scientists understand when they formed and how they change – and, in the case of planets, if <a href="https://theconversation.com/ancestor-of-all-life-on-earth-evolved-earlier-than-we-thought-according-to-our-new-timescale-101752">life has had time to have evolved on them</a>.</p>
<p>Unfortunately, age is hard to measure for objects in space.</p>
<p>Stars like the Sun maintain the same <a href="https://en.wikipedia.org/wiki/Stellar_evolution">brightness, temperature and size for billions of years</a>. Planet properties <a href="https://en.wikipedia.org/wiki/Planetary_equilibrium_temperature">like temperature</a> are often set by the star they orbit rather than their own age and evolution.</p>
<p>Determining the age of a star or planet can be as hard as guessing the age of a person who looks exactly the same from childhood to retirement. </p>
<h2>Sussing out a star’s age</h2>
<p>Fortunately, <a href="http://astronomy.nmsu.edu/jasonj/565/docs/11_07.pdf">stars change subtly</a> in brightness and color over time. With very accurate measurements, astronomers can compare these measurements of a star to <a href="https://doi.org/10.3847/0067-0049/222/1/8">mathematical models</a> that predict what happens to stars as they get older and estimate an age from there. </p>
<p>Stars don’t just glow, they also spin. Over time, <a href="https://doi.org/10.1086/151310">their spinning slows down</a>, similar to how a spinning wheel slows down when it encounters friction. By comparing the spin speeds of stars of different ages, astronomers have been able to <a href="https://doi.org/10.1086/367639">create mathematical relationships for the ages of stars</a>, a method known as <a href="https://en.wikipedia.org/wiki/Gyrochronology">gyrochronology</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up image of the Sun in outer space" src="https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=567&fit=crop&dpr=1 600w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=567&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=567&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=713&fit=crop&dpr=1 754w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=713&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/530378/original/file-20230606-25-mkkjms.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=713&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Researchers estimate the Sun is 4.58 billion years old.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/in-this-handout-photo-provided-by-nasa-a-solar-and-news-photo/2740385?adppopup=true">NASA via GettyImages</a></span>
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</figure>
<p>A star’s spin also generates a strong magnetic field and produces magnetic activity, such as <a href="https://en.wikipedia.org/wiki/Solar_flare">stellar flares</a> – powerful bursts of energy and light that occur on stars’ surfaces. A steady decline in magnetic activity from a star can also help estimate its age.</p>
<p>A more advanced method for determining the ages of stars is called <a href="https://en.wikipedia.org/wiki/Asteroseismology">asteroseismology</a>, or star shaking. Astronomers study vibrations on the surfaces of stars caused by waves that travel through their interiors. Young stars have different vibrational patterns than old stars. By using this method, <a href="https://doi.org/10.1051/0004-6361/201526419">astronomers have estimated</a> the Sun to be 4.58 billion years old.</p>
<h2>Piecing together a planet’s age</h2>
<p>In the solar system, <a href="https://en.wikipedia.org/wiki/Radionuclide">radionuclides</a> are the key to dating planets. These are special atoms that slowly release energy over a long period of time. As natural clocks, radionuclides help scientists determine the ages of all kinds of things, from <a href="https://www.nps.gov/subjects/geology/radiometric-age-dating.htm">rocks</a> to <a href="https://theconversation.com/radiocarbon-dating-only-works-half-the-time-we-may-have-found-the-solution-189493">bones</a> and <a href="https://physicsworld.com/a/archaeological-dating-by-re-firing-ancient-pots/">pottery</a>.</p>
<p>Using this method, scientists have determined that the oldest known meteorite is <a href="https://doi.org/10.1073/pnas.2026129118">4.57 billion years old</a>, almost identical to the Sun’s asteroseismology measurement of 4.58 billion years. The oldest known rocks on Earth have slightly younger ages of <a href="https://doi.org/10.1038/35051550">4.40 billion years</a>.
Similarly, soil brought back from the Moon during the Apollo missions had <a href="https://doi.org/10.1016/0012-821X(70)90093-2">radionuclide ages of up to 4.6 billion years</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up image of craters on the surface of the moon." src="https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/535816/original/file-20230705-7861-tqlx1p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Craters on the moon’s surface.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/mondoberfl%C3%A4che-royalty-free-image/1174421451?phrase=crater+moon&adppopup=true">Tomekbudujedomek/Moment via Getty Images</a></span>
</figcaption>
</figure>
<p>Although studying radionuclides is a powerful method for measuring the ages of planets, it usually requires having a rock in hand. Typically, astronomers only have a picture of a planet to go by. Astronomers often determine the ages of rocky space objects like Mars or the Moon by <a href="https://en.wikipedia.org/wiki/Crater_counting#:%7E:text=Crater%20counting%20is%20a%20method,rate%20that%20is%20assumed%20known.">counting their craters</a>. Older surfaces have more craters than younger surfaces. However, erosion from water, wind, <a href="https://phys.org/news/2021-09-cosmic-rays-erode-largest-interstellar.html">cosmic rays</a> and lava flow from volcanoes can wipe away evidence of earlier impacts.</p>
<p>Aging techniques don’t work for giant planets like Jupiter that have deeply buried surfaces. However, astronomers can estimate their ages by <a href="https://doi.org/10.1016/j.icarus.2020.114184">counting craters on their moons</a> or studying the <a href="https://doi.org/10.1073/pnas.1704461114">distribution of certain classes of meteorites</a> scattered by them, which are consistent with radionuclide and cratering methods for rocky planets.</p>
<p>We cannot yet directly measure the ages of planets outside our solar system with current technology.</p>
<h2>How accurate are these estimates?</h2>
<p>Our own solar system provides the best check for accuracy, since astronomers can compare the radionuclide ages of rocks on the Earth, Moon, or asteroids to the asteroseismology age of the Sun, and these match very well. </p>
<p>Stars in clusters like the <a href="https://en.wikipedia.org/wiki/Pleiades">Pleiades</a> or <a href="https://en.wikipedia.org/wiki/Omega_Centauri">Omega Centauri</a> are believed to have all formed at roughly the same time, so age estimates for individual stars in these clusters should be the same. In some stars, <a href="https://ui.adsabs.harvard.edu/abs/2023ApJ...948..122S/abstract">astronomers can detect</a> radionuclides like uranium – a heavy metal found in rocks and soil – in their atmospheres, which have been used to check the ages from other methods. </p>
<p>Astronomers believe planets are roughly the same age as their host stars, so improving methods to determine a star’s age helps determine a planet’s age as well. By studying subtle clues, it’s possible to make an educated guess of the age of an otherwise steadfast star.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/205809/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Burgasser receives funding from NASA and the National Science Foundation.</span></em></p>
Measuring the ages of planets and stars is tricky. An observational astrophysicist describes the subtle clues that provide good estimates for how old different space objects are.
Adam Burgasser, Professor of Astronomy & Astrophysics, University of California, San Diego
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/207186
2023-09-25T12:20:49Z
2023-09-25T12:20:49Z
Why does a plane look and feel like it’s moving more slowly than it actually is?
<figure><img src="https://images.theconversation.com/files/537863/original/file-20230717-230575-4lcw35.jpg?ixlib=rb-1.1.0&rect=157%2C431%2C2434%2C1432&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Without a point of reference, it can be hard to tell just how fast an airplane is traveling.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/an-aircraft-flies-through-london-skies-leaving-a-vapour-news-photo/73179201?adppopup=true">Daniel Berehulak/Getty Images News via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why does a plane look and feel like it’s moving more slowly than it actually is? – Finn F., age 8, Concord, Massachusetts</strong></p>
</blockquote>
<hr>
<p><a href="https://www.flyingmag.com/guides/how-fast-do-commerical-planes-fly/">A passenger jet flies</a> at about 575 mph once it’s at cruising altitude. That’s nearly nine times faster than a car might typically be cruising on the highway. So why does a plane in flight look like it’s just inching across the sky?</p>
<p><a href="https://www.engineering.iastate.edu/people/profile/sdnelson/">I am an aerospace educator</a> who relies on the laws of physics when teaching about aircraft. These same principles of physics help explain why looks can be deceiving when it comes to how fast an object is moving.</p>
<h2>Moving against a featureless background</h2>
<p>If you watch a plane accelerating toward takeoff, it appears to be moving very quickly. It’s not until the plane is in the air and has reached cruising altitude that it appears to be moving very slowly. That’s because there is often no independent reference point when the plane is in the sky.</p>
<p>A reference point is a way to measure the speed of the airplane. If there are no <a href="https://www.nasa.gov/sites/default/files/atoms/files/contrails_k-12.pdf">contrails</a> or clouds surrounding it, the plane is moving against a completely uniform blue sky. This can make it very hard to perceive just how fast a plane is moving. </p>
<p>And because the plane is far away, it takes longer for it to move across your field of vision compared to an object that is close to you. This further creates the illusion that it is moving more slowly than it actually is.</p>
<p>These factors explain why a plane looks like it’s going more slowly than it is. But why does it feel that way, too?</p>
<h2>A passenger’s perception on the plane</h2>
<p>A plane feels like it’s traveling more slowly than it is because, just like when you look up at a plane in the sky, as a passenger on a plane, you have no independent reference point. You and the plane are moving at the same speed, which can make it difficult to perceive your rate of motion relative to the ground beneath you. This is the same reason why it can be hard to tell that you are driving quickly on a highway that is surrounded only by empty fields with no trees.</p>
<figure class="align-center ">
<img alt="Perspective from a plane window of the plane's shadow against a brown field with the plane's white wing visible on the left side." src="https://images.theconversation.com/files/537920/original/file-20230717-228467-6a2tmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537920/original/file-20230717-228467-6a2tmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=405&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537920/original/file-20230717-228467-6a2tmx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=405&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537920/original/file-20230717-228467-6a2tmx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=405&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537920/original/file-20230717-228467-6a2tmx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=509&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537920/original/file-20230717-228467-6a2tmx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=509&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537920/original/file-20230717-228467-6a2tmx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=509&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Watching the speed of a plane’s shadow can help you assess how quickly a plane is moving.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-shadow-of-us-secretary-of-state-antony-blinkens-news-photo/1232956715?adppopup=true">Saul Loeb/AFP via GettyImages</a></span>
</figcaption>
</figure>
<p>However, there are a couple of ways you might be able to understand just how fast you are moving.</p>
<p>Can you <a href="https://www.istockphoto.com/video/silhouette-of-airplane-flying-over-fields-shadow-of-plane-is-landing-over-golden-gm1194290281-340013766">see the plane’s shadow</a> on the ground? It can give you perspective on how fast the plane is moving relative to the ground. If you are lucky enough to spot it, you will be amazed at how fast the plane’s shadow passes over buildings and roads. You can get a real sense of the 575 mph average speed of a cruising passenger plane. </p>
<p>Another way to understand how fast you are moving is to note how fast thin, spotty cloud cover moves over the wing. This reference point gives you another way to “see” or perceive your speed. Remember though, that <a href="https://www.coolkidfacts.com/how-fast-do-clouds-move/">clouds aren’t typically stationary</a>; they’re just moving very slow relative to the plane. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/xN4gFboXjtc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An airplane passes over thin, spotty cloud cover.</span></figcaption>
</figure>
<p>Although it can be difficult to discern just how fast a plane is actually moving, using reference points to gain perspective can help tremendously.</p>
<p>Has your interest in aviation been sparked? If so, there are a lot of great career opportunities <a href="https://www.nasa.gov/topics/aeronautics/index.html">in aeronautics</a>.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/207186/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sara Nelson does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
An aerospace engineer explains why it’s so hard to tell just how fast an airplane is really moving.
Sara Nelson, Director of the NASA Iowa Space Grant Consortium, Iowa State University
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/204789
2023-09-18T12:19:01Z
2023-09-18T12:19:01Z
What happens if you need to pee while you’re asleep?
<figure><img src="https://images.theconversation.com/files/536919/original/file-20230711-19-qt6put.jpg?ixlib=rb-1.1.0&rect=703%2C209%2C4288%2C2597&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Your bladder can signal the brain when it's full, even while you're asleep.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/toilet-bowl-in-the-restroom-dramatic-lighting-copy-royalty-free-image/1303857822?adppopup=true">Happyphoton/iStock via Getty Images</a></span></figcaption></figure><p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>What happens if you have to go to the bathroom in your sleep? – Calleigh H., age 11, Oklahoma</strong></p>
</blockquote>
<hr>
<p>As you drink water during the day, your body turns extra liquid it doesn’t need into pee. Your bladder stores the urine and eventually alerts you when it’s time to take a trip to the toilet.</p>
<p>But what about at night? How does your body know not to pee while you’re asleep?</p>
<p>Just because you’re snoozing doesn’t mean your body is totally offline – continuous processes like breathing, digestion and, yes, making pee, still happen while you’re asleep. Your bladder and your brain work together to know what to do with that big glass of water you drank before bed.</p>
<p>Using the bathroom every day is routine for many people, so it’s something you might not pay much attention to. But as a <a href="https://www.seattlechildrens.org/directory/jennifer-jihyun-ahn/">pediatric urologist</a>, understanding how the brain and bladder work together – and sometimes miscommunicate – is an important part of my job. </p>
<h2>The bladder and the brain</h2>
<p>The bladder has two main jobs: to safely store urine and to empty it out. While it seems simple, these two tasks take <a href="https://www.mea.elsevierhealth.com/campbell-walsh-wein-urology-9780323546423.html">a lot of complex coordination</a> of muscles and nerves – that’s the brain’s job.</p>
<p>For babies and young kids, the bladder has reflexes, meaning it automatically knows when to squeeze the muscles to empty the urine. Since babies can’t control this consciously, they typically wear diapers. But <a href="https://www.seattlechildrens.org/health-safety/keeping-kids-healthy/development/toliet-potty-training/">as kids grow</a>, the bladder muscles and nerves also grow, which gives a youngster more control over their bladder. </p>
<p>During <a href="https://pubmed.ncbi.nlm.nih.gov/31613577/">toilet training</a>, which usually happens by the age of 3 or 4 in the U.S., kids learn how to use the toilet voluntarily. This means that they can feel when the bladder is getting full and their brain can receive and understand that signal. The brain can then tell the bladder to “hold it” until they’ve made it to the toilet and it’s safe to pee.</p>
<h2>What happens in sleep mode?</h2>
<p>Most children first learn how to use the toilet during the day. Using the bathroom overnight <a href="https://www.healthychildren.org/English/ages-stages/toddler/toilet-training/Pages/Bedwetting.aspx">can be more difficult</a> because the sleeping brain doesn’t receive signals in the same way as when awake. </p>
<p>While awake, if there’s a loud noise or a bright light, the body senses it and reacts. But during sleep, the body may not hear that noise or see that light because the brain is in <a href="https://doi.org/10.1016/j.smrv.2019.101228">sleep mode</a>. Imagine sleeping through an overnight thunderstorm that you didn’t realize happened until you hear people talking about it in the morning. Your brain didn’t process the loud noises because it was focusing on sleep.</p>
<p>The same thing can happen with bladder signals. The bladder fills with urine 24 hours a day, even while you’re snoozing, and it sends signals to the brain when it’s full. In order to help you get enough sleep, your brain will tell your bladder to hold it until morning.</p>
<p>Sometimes, if you really need to go, your brain will tell your body to wake up so you can go empty your full bladder. While it’s normal to wake up to pee sometimes – especially if you drank a big cup of hot chocolate right before bed – most older kids can usually sleep through the night without needing to use the toilet.</p>
<p><div data-react-class="InstagramEmbed" data-react-props="{"url":"https://www.instagram.com/p/CseFST5M8Ur/?hl=en","accessToken":"127105130696839|b4b75090c9688d81dfd245afe6052f20"}"></div></p>
<p>When the brain and bladder are working together well, your bladder gradually fills up overnight and hangs on til morning when you stumble into the bathroom to empty it.</p>
<h2>Nighttime accidents</h2>
<p>But there are many ways the communication between the brain and the bladder can break down. For one, the brain may not get the bladder’s message that it’s time to go. Even if the brain gets the message, it may not be able to tell the bladder to hold on. Or, when the bladder can’t wait, the brain might not tell your body to wake up. If the signals and messages aren’t sent, or are received incorrectly, the bladder will go into <a href="https://doi.org/10.1016/j.smrv.2019.101228">reflex mode</a> – it squeezes to empty itself of pee, even though you’re fast asleep in bed.</p>
<p>Wetting the bed at night, which doctors call nocturnal <a href="https://www.britannica.com/science/enuresis">enuresis</a>, is more common than you might think. <a href="https://www.healthychildren.org/English/ages-stages/toddler/toilet-training/Pages/Bedwetting.aspx">About 15%</a> of kids between ages 5 and 7 wet the bed sometimes. Even some teenagers experience it. It’s more common in boys, and often there’s a family history, meaning parents or relatives may have dealt with nighttime accidents too.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/536921/original/file-20230711-19-pfnduo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A child's legs, wearing pajama pants, against a grey floor. A wet stain is visible on their bottom and on the ground behind them." src="https://images.theconversation.com/files/536921/original/file-20230711-19-pfnduo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/536921/original/file-20230711-19-pfnduo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536921/original/file-20230711-19-pfnduo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536921/original/file-20230711-19-pfnduo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536921/original/file-20230711-19-pfnduo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536921/original/file-20230711-19-pfnduo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536921/original/file-20230711-19-pfnduo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Many children wet the bed at night.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/unrecognizable-child-legs-on-wet-bed-incontinence-royalty-free-image/1398170112?adppopup=true">Olga Rolenko/Moment via Getty Images</a></span>
</figcaption>
</figure>
<p>There are a few reasons why nighttime wetting happens. Since kids’ brains are growing and developing, nighttime communication between the brain and bladder can take longer. </p>
<p>Some bodies make more pee at night, making it more likely the bladder will get full during sleep. Some people have smaller bladders that fill up fast. Sometimes having difficulties with sleep or being a deep sleeper <a href="https://doi.org/10.1016/j.smrv.2019.101228">can make it harder</a> to wake up at night if you really need to pee.</p>
<p>Most kids who wet the bed at night outgrow it as their brains and bodies continue to develop. At that point, they can sleep through the night without needing to pee, or their bodies are able to wake up at night to use the bathroom when they need to. </p>
<p>If wetting the bed is an issue, there are <a href="https://www.healthychildren.org/English/health-issues/conditions/genitourinary-tract/Pages/Nocturnal-Enuresis-in-Teens.aspx">some things that can help</a>, like drinking less liquid in the evening or using the bathroom right before you go to bed. These precautions make it less likely that the bladder will be too full during sleep. There are also bedwetting alarms that can help train the body to wake up when the bladder needs to be emptied. If there are concerns about nighttime accidents, or if accidents start happening in older children, I recommend consulting a doctor. </p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/204789/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jennifer Ahn does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
A pediatric urologist explains how the bladder and the brain communicate to wake you up when you need to ‘go’ – and how that communication might break down.
Jennifer Ahn, Assistant Professor of Urology, School of Medicine, University of Washington
Licensed as Creative Commons – attribution, no derivatives.