tag:theconversation.com,2011:/africa/topics/thermodynamics-7676/articlesThermodynamics – The Conversation2024-02-02T13:17:06Ztag:theconversation.com,2011:article/2208182024-02-02T13:17:06Z2024-02-02T13:17:06ZHow can I get ice off my car? An engineer who studies airborne particles shares some quick and easy techniques<figure><img src="https://images.theconversation.com/files/572255/original/file-20240130-29-7n5wna.jpeg?ixlib=rb-1.1.0&rect=0%2C3%2C1024%2C763&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Condensation and cold combine to create that layer of ice on car windshields in winter. </span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Oblodzone_szyby_samochodu,_zima_2009_%28ubt%29.jpeg">Tomasz Sienicki/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>If you live somewhere that gets cold in the winter, you’ve probably seen cars parked outdoors covered in a thin layer of ice on a chilly morning. But what causes this frost, and how can you get rid of it quickly?</p>
<p>I’m a <a href="https://scholar.google.com/citations?user=xcpTqRYAAAAJ&hl=en">mechanical engineering professor</a> who studies how water vapor interacts with airborne particles under different atmospheric conditions. Frosty windshields are similar to some of the thermodynamic questions I study in the lab, and they’re also a pesky issue that I deal with every winter on my way to work. </p>
<h2>Windshield condensation</h2>
<p>The air in Earth’s atmosphere always contains a certain amount of water vapor, but there’s only so much water vapor the air can hold. Scientists call that limit 100% <a href="https://www.britannica.com/science/humidity">relative humidity</a>. <a href="https://www.weather.gov/arx/why_dewpoint_vs_humidity">The dew point</a> refers to the temperature at which relative humidity reaches 100%. </p>
<p>Wet air has high dew point temperature, while dry air has a low dew point temperature. With each degree drop in temperature, the air gets closer to its dew point temperature – or its water vapor carrying capacity. Any cooling after the dew point temperature has been reached causes <a href="https://sealevel.jpl.nasa.gov/ocean-observation/understanding-climate/air-and-water/">water to condense onto surfaces</a>, or form into fog.</p>
<p>Overnight, car windshields facing the cold dark sky are <a href="https://www.energy.gov/energysaver/principles-heating-and-cooling">radiatively cooled</a>, meaning they release heat out into their surrounding area in the form of visible and invisible light. As air comes in contact with the cold windshield, it can reach its dew point temperature. Then, the water vapor condenses onto the windshield.</p>
<p>When this radiative cooling drops the temperature on the windshield’s surface to <a href="https://www.britannica.com/science/freezing-point">below the freezing point</a>, 32 degrees Fahrenheit (zero degrees Celsius), the layer of condensed water on the windshield turns to frost. </p>
<h2>Defrosting your car</h2>
<p>To defrost an icy windshield, you can follow a few different approaches, some of which take longer and require more effort than others.</p>
<p>One option is to directly spray a small amount of warm liquid on the layer of frost to help melt it. For this approach to work, the spray liquid must be hot enough to raise the overall temperature of the frost layer to above <a href="https://pubchem.ncbi.nlm.nih.gov/ptable/melting-point/">the melting point</a>. But the temperature can’t be way hotter than the temperature of the glass or you’ll crack your windshield. </p>
<p>A better way to melt the ice without damaging your car is to spray your windows with a warm liquid that has a lower freezing point than water, like a mixture of rubbing alcohol and water. This warm mixture will melt the frost layer without heating up the glass, and the resulting liquid layer on the windshield will have a lower freezing point than water. It will remain liquid, and you can wipe it away with your windshield wipers. </p>
<p>Similar alcohol and water mixtures – <a href="https://www.britannica.com/science/glycol">glycol, for example</a> – are commonly used to maintain the <a href="https://mayekawa.es/images/pdf/ASHRAE_ENERGY_EFFICIENT_ICE_RINK_2015.pdf">icy surface of skating rinks</a>.</p>
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<figcaption><span class="caption">A mix of water and rubbing alcohol can melt ice on your windshield.</span></figcaption>
</figure>
<p>This approach can melt the ice reasonably quickly and easily, without too much effort. You don’t even have to turn on your car. </p>
<p>If you have a little more time, you can start the car and run <a href="https://www.lifewire.com/how-do-car-defrosters-work-534663">the air defrost system</a> to blow hot air – aim for above 80 degrees Fahrenheit – onto the inside of the windshield. This warms the windshield and will eventually melt the frost layer. Once you see some melting, you can use the windshield wipers to wipe the rest of the ice away. </p>
<p>This option consumes more energy, as your car will have to heat up the windshield, but it doesn’t require you to do much. </p>
<p>Using the defrost system to blow warm air toward the windshield will also help to clear the inside of the windshield when it gets fogged up from condensation. Otherwise, if it’s dry outside, you can also clear up windshield fog by opening the car window and letting in outside air.</p>
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<a href="https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A person wearing a winter jacket uses a scraper on their frost-covered windshield." src="https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=497&fit=crop&dpr=1 754w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=497&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=497&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">You can use an ice scraper to break the ice on your windshield into chunks, so your wiper blades can clean them off.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/ColoradoWeather/c8d71e03eb5144afad7c01e72eccf5c2/photo?Query=windshield%20wipers&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=296&digitizationType=Digitized&currentItemNo=17&vs=true&vs=true">AP Photo/David Zalubowski</a></span>
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<p>If you are in a hurry or need some exercise, you can use an ice scraper to break up frost on your windshield, creating smaller islands of ice. The windshield wiper can then mechanically dislodge the chunks by moving them around and melting them. This requires more energy on your part, but it doesn’t require much from your car.</p>
<p>If you have a relaxed start to your day, you can let the Sun warm the windshield and slowly melt the frost layer for you. This technique saves energy in every way imaginable.</p><img src="https://counter.theconversation.com/content/220818/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suresh Dhaniyala 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>When you’re running late in the winter, you don’t want to have to spend time scraping frost off your windshield. Try some expert-recommended techniques instead.Suresh Dhaniyala, Bayard D. Clarkson Distinguished Professor of Mechanical and Aeronautical Engineering, Clarkson UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2138362023-11-13T13:33:49Z2023-11-13T13:33:49ZIs 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>
<hr>
<blockquote>
<p><strong>Will it ever be possible for time travel to occur? – Alana C., age 12, Queens, New York</strong></p>
</blockquote>
<hr>
<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>
<figure>
<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>
</figure>
<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 CountyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1962712023-01-24T13:23:42Z2023-01-24T13:23:42ZDevice transmits radio waves with almost no power – without violating the laws of physics<figure><img src="https://images.theconversation.com/files/505483/original/file-20230119-19742-3pzdvg.jpeg?ixlib=rb-1.1.0&rect=0%2C12%2C4031%2C3005&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This experimental setup shows an ultra-low-power wireless communications device that could one day be used in tiny remote sensors.</span> <span class="attribution"><span class="source">Zerina Kapetanovic</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>A new ultra-low-power method of communication at first glance seems to violate the laws of physics. It is possible to wirelessly transmit information simply by opening and closing a switch that connects a resistor to an antenna. No need to send power to the antenna.</p>
<p>Our system, combined with techniques for <a href="https://doi.org/10.1109/JSAC.2018.2872615">harvesting energy from the environment</a>, could lead to all manner of devices that transmit data, including tiny sensors and implanted medical devices, without needing batteries or other power sources. These include sensors for <a href="https://www.usenix.org/conference/nsdi17/technical-sessions/presentation/vasisht">smart agriculture</a>, <a href="https://doi.org/10.1038/s41551-021-00683-3">electronics implanted in the body</a> that never need battery changes, better <a href="https://doi.org/10.4018/JGIM.2020100108">contactless credit cards</a> and maybe even new ways for <a href="https://www.nasa.gov/smallsat-institute/sst-soa/communications">satellites</a> to communicate. </p>
<p>Apart from the energy needed to flip the switch, no other energy is needed to transmit the information. In our case, the switch is a transistor, an electrically controlled switch with no moving parts that consumes a minuscule amount of power.</p>
<p>In the simplest form of ordinary radio, a switch connects and disconnects a strong electrical signal source – perhaps an oscillator that produces a sine wave fluctuating 2 billion times per second – to the <a href="https://academy.wedio.com/what-is-a-transmitter/">transmit antenna</a>. When the signal source is connected, the antenna produces a radio wave, denoting a 1. When the switch is disconnected, there is no radio wave, indicating a 0.</p>
<p>What we showed is that a powered signal source is not needed. Instead, random thermal noise, present in all electrically conductive materials because of the heat-driven motion of electrons, can take the place of the signal driving the antenna. </p>
<h2>No free lunch</h2>
<p>We are <a href="https://scholar.google.com/citations?user=LnAus20AAAAJ&hl=en">electrical engineers</a> who <a href="https://scholar.google.com/citations?user=HEb5C1wAAAAJ&hl=en">research wireless systems</a>. During the peer review of <a href="https://doi.org/10.1073/pnas.2201337119">our paper</a> about this research, published recently in Proceedings of the National Academy of Sciences, reviewers asked us to explain why the method did not violate the <a href="https://www.semanticscholar.org/paper/Demons%2C-Engines-and-the-Second-Law-Bennett/2480bf5e7b41a5b6d1db92e3387d7214bc68a49c">second law of thermodynamics</a>, the main law of physics that explains why <a href="https://engineering.mit.edu/engage/ask-an-engineer/is-it-possible-to-construct-a-perpetual-motion-machine/">perpetual motion machines</a> are not possible. </p>
<p>Perpetual motion machines are theoretical machines that can work indefinitely without requiring energy from any external source. The reviewers worried that if it were possible to send and receive information with no powered components, and with both the transmitter and receiver at the same temperature, that would mean that you could create a perpetual motion machine. Because this is impossible, it would imply that there was something wrong with our work or our understanding of it. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/505660/original/file-20230120-12-rlgt9p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A graphic in the top half showing a horizontal cylinder on the left with a pipe extending to the right with a 90-degree bend upward connecting to an upside-down triangle with pairs of curved lines on either side, and in the bottom half the same but disconnected" src="https://images.theconversation.com/files/505660/original/file-20230120-12-rlgt9p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505660/original/file-20230120-12-rlgt9p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=512&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505660/original/file-20230120-12-rlgt9p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=512&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505660/original/file-20230120-12-rlgt9p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=512&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505660/original/file-20230120-12-rlgt9p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=643&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505660/original/file-20230120-12-rlgt9p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=643&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505660/original/file-20230120-12-rlgt9p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=643&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Electrons that naturally move around inside a room-temperature resistor affect electrons in a connected antenna, which causes the antenna to generate radio waves. Connecting and disconnecting the antenna produces the ones and zeros of a binary signal.</span>
<span class="attribution"><span class="source">Zerina Kapetanovic</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>One way the second law can be stated is that heat will flow spontaneously only from hotter objects to colder objects. The wireless signals from our transmitter transport heat. If there were a spontaneous flow of signal from the transmitter to the receiver in the absence of a temperature difference between the two, you could harvest that flow to get free energy, in violation of the second law. </p>
<p>The resolution of this seeming paradox is that the receiver in our system is powered and acts like a refrigerator. The signal-carrying electrons on the receive side are effectively kept cold by the powered amplifier, similar to how a refrigerator keeps its interior cold by continuously pumping heat out. The transmitter consumes almost no power, but the receiver consumes substantial power, up to 2 watts. This is similar to receivers in other ultra-low-power communications systems. Nearly all of the power consumption happens at a base station that does not have constraints on energy use.</p>
<h2>A simpler approach</h2>
<p>Many researchers worldwide have been exploring related passive communication methods, known as <a href="https://doi.org/10.1145/2534169.2486015">backscatter</a>. A backscatter data transmitter looks very similar to our data transmitter device. The difference is that in a backscatter communication system, in addition to the data transmitter and the data receiver, there is a third component that generates a radio wave. The switching performed by the data transmitter has the effect of reflecting that radio wave, which is then picked up at the receiver. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/gX9cbxLSOkE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An example of backscatter unpowered wireless communications.</span></figcaption>
</figure>
<p>A <a href="https://doi.org/10.23919/JCIN.2019.8917868">backscatter device</a> has the same energy efficiency as our system, but the backscatter setup is much more complex, since a <a href="https://www.atlasrfidstore.com/rfid-insider/explaining-backscatter-from-basic-to-advanced-principles">signal-generating component</a> is needed. However, our system has lower data rate and range than either backscatter radios or conventional radios.</p>
<h2>What’s next</h2>
<p>One area for future work is to improve our system’s data rate and range, and to test it in applications such as implanted devices. For implanted devices, an advantage of our new method is that there is no need to expose the patient to a strong external radio signal, which can cause tissue heating. Even more exciting, we believe that related ideas could enable other new forms of communication in which other natural signal sources, such as thermal noise from biological tissue or other electronic components, can be modulated. </p>
<p>Finally, this work may lead to new connections between the study of heat (thermodynamics) and the study of communication (information theory). These fields are often viewed as analogous, but this work suggests some more literal connections between them.</p><img src="https://counter.theconversation.com/content/196271/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joshua R. Smith receives funding from the National Science Foundation, the National Institutes of Health, the Department of Energy, the Department of Defense Medical Command, DARPA, Bosch, and Amazon. He is a co-founder of start up companies Jeeva Wireless, Wibotic, and Proprio. </span></em></p><p class="fine-print"><em><span>Zerina Kapetanovic's Ph.D. work was funded by a Microsoft Research Dissertation Grant. She is currently a Postdoctoral Researcher at Microsoft. </span></em></p>A wireless transmitter uses almost no power and at first glance appears to violate the laws of physics. It’s actually a clever use of physics that could one day transmit data from tiny remote sensors.Joshua R. Smith, Professor of Electrical and Computer Engineering and of Computer Science and Engineering, University of WashingtonZerina Kapetanovic, Acting Assistant Professor of Electrical Engineering, Stanford UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1781642022-03-02T19:06:23Z2022-03-02T19:06:23Z‘An ever-ticking clock’: we made a ‘time crystal’ inside a quantum computer<figure><img src="https://images.theconversation.com/files/449403/original/file-20220302-19-1y1gl9r.jpg?ixlib=rb-1.1.0&rect=4%2C4%2C2991%2C1989&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">IBM</span></span></figcaption></figure><p>You probably know what a crystal is. We’ve all seen one, held one in our hands, and even tasted one on our tongue (for instance sodium chloride crystals, also known as “salt”). </p>
<p>But what on earth is a “time crystal”, if not a sci-fi gadget in the latest Marvel movie? Why do we need a quantum computer to make one? And what is a quantum computer anyway?</p>
<h2>Bits and qubits</h2>
<p>Let’s start there. Computers are all around us. Some are compact, portable and primarily used to stream Netflix, while others fill entire rooms and simulate complex phenomena like the weather or the evolution of our Universe. </p>
<p>Regardless of the details, on a fundamental level computers all have the same purpose: processing information. The information is stored and processed in “bits”.</p>
<p>Any physical system with two identifiably distinct states (call them “0” and “1”) can serve as a bit. Connect lots of bits together in the right way and you can do arithmetic, logic, or what we generally call “computation”. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/449412/original/file-20220302-21-a4jhrz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/449412/original/file-20220302-21-a4jhrz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=389&fit=crop&dpr=1 600w, https://images.theconversation.com/files/449412/original/file-20220302-21-a4jhrz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=389&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/449412/original/file-20220302-21-a4jhrz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=389&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/449412/original/file-20220302-21-a4jhrz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=489&fit=crop&dpr=1 754w, https://images.theconversation.com/files/449412/original/file-20220302-21-a4jhrz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=489&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/449412/original/file-20220302-21-a4jhrz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=489&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A conventional bit can take the values of 0 or 1 - but a quantum bit or qubit can take on a range of complex values in between.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Now, it turns out that the physical world on a very fundamental level is governed by the strange rules of quantum physics. You can also make a quantum version of a bit, called a quantum bit or “qubit”.</p>
<p>Qubits can also be described in terms of two states, “0” and “1”, except they can be both “0” and “1” <em>at the same time</em>. This allows for a much richer form of information processing, and hence more powerful computers.</p>
<h2>What can we do with quantum computers?</h2>
<p>Much of the current research in this area is focused either on building a working quantum computer – a challenging engineering task indeed – or on designing algorithms to do things we can’t manage with our current, classical computers.</p>
<p>Our research, however, is focused on an application first envisioned by the famous US physicist Richard Feynman more than 30 years ago: to use quantum computers to conduct research in fundamental physics. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-quantum-computation-and-communication-technology-7892">Explainer: quantum computation and communication technology </a>
</strong>
</em>
</p>
<hr>
<p>As theorists, we typically use a combination of pen-and-paper mathematics and computer simulations to study physical systems. Unfortunately, conventional computers are very ill-equipped for simulating quantum physics. </p>
<p>This is where quantum computers come in. They are already quantum in nature and can, in principle, behave like any quantum system we wish to investigate.</p>
<p>Using IBM’s quantum computer we were able to achieve precisely that, turning it into an experimental simulator to create a novel state of matter, just as envisioned by Feynman. This machine is located in America but can be accessed remotely by researchers around the globe. </p>
<p>Being able to access quantum computers from anywhere in the world represents a major shift in this kind of quantum research.</p>
<h2>Time crystals</h2>
<p>The special type of quantum system we created is called <a href="https://doi.org/10.1126/sciadv.abm7652">a “time crystal”</a>. </p>
<p>I hope you will not be too disappointed when I say you will probably not get to hold one of these in your hands any time soon. But maybe we can at least understand what a time crystal is! </p>
<p>The crucial idea here is that matter exists in different “phases”, like the three familiar phases of water: ice, water and steam. A material can have very different properties depending on which phase we find it in. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/449409/original/file-20220302-27-1gvzn6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/449409/original/file-20220302-27-1gvzn6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=525&fit=crop&dpr=1 600w, https://images.theconversation.com/files/449409/original/file-20220302-27-1gvzn6b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=525&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/449409/original/file-20220302-27-1gvzn6b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=525&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/449409/original/file-20220302-27-1gvzn6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=660&fit=crop&dpr=1 754w, https://images.theconversation.com/files/449409/original/file-20220302-27-1gvzn6b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=660&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/449409/original/file-20220302-27-1gvzn6b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=660&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">In a conventional crystal, particles are arranged regularly in space. In a time crystal, they’re arranged regularly in time.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Now a conventional crystal – we might actually call it a “space crystal” - is one such phase of matter. Crystals are characterised by a very regular arrangement of particles in space. </p>
<p>In a time crystal, particles are not only arranged regularly in space, but also in <em>time</em>. The particles move from one position to another and back again, without slowing down or losing energy. </p>
<p>Now this is truly different from what we usually deal with. </p>
<h2>Beyond equilibrium</h2>
<p>The types of phases we normally encounter all have on thing in common: they are in “thermal equilibrium”. If you leave a hot cup of coffee sitting on your desk it will transfer heat to its surroundings until it reaches the same temperature as your room, and then it stops and no changes happen from then on. </p>
<p>If you carefully add a layer of cream to your – now unfortunately cold – coffee and begin stirring, you will see changes happen in time. Coffee and cream will mix in beautiful swirls until the whole thing turns into a uniform light brown liquid, and nothing really changes after that. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/449419/original/file-20220302-27-2wlksd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/449419/original/file-20220302-27-2wlksd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/449419/original/file-20220302-27-2wlksd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/449419/original/file-20220302-27-2wlksd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/449419/original/file-20220302-27-2wlksd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/449419/original/file-20220302-27-2wlksd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/449419/original/file-20220302-27-2wlksd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Coffee and milk mixed together will create beautiful swirls before eventually reaching a uniform light-brown equilibrium.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>These are examples of “equilibrium”. The common theme is that things in equilibrium do not change over time. </p>
<p>Our time crystal violates this condition. It actually keeps changing indefinitely, for all eternity, without ever reaching equilibrium. </p>
<h2>A loophole in the laws of thermodynamics?</h2>
<p>A time crystal therefore constitutes an out-of-equilibrium phase - in fact, it is one of the first examples of such a strange state of matter. It is essentially like an ever-ticking clock that neither loses energy, nor requires a supply of energy to keep going. </p>
<p>This seems dangerously close to a perpetual motion machine, which would violate the laws of thermodynamics. </p>
<p>But the first law of thermodynamics – which says energy is not created or destroyed - is not in any danger here, as we can’t extract energy from a time crystal while also keeping it running. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/unpacking-a-mystery-of-physics-why-processes-in-nature-operate-only-in-one-direction-177556">Unpacking a mystery of physics: Why processes in nature operate only in one direction</a>
</strong>
</em>
</p>
<hr>
<p>The second law states that things left to themselves can only become more disordered over time. This concept is probably all too familiar to anyone with kids or housemates.</p>
<p>But there is a loophole. The second law forbids things from becoming more ordered with time, but it doesn’t say they can’t maintain their current level of disorderedness forever.</p>
<p>In everyday life, we don’t see this loophole in action. It is the equivalent of stirring away at your coffee and cream and finding that the swirling tendrils of cream never fully mix with the coffee. </p>
<p>This is what time crystals do. We don’t see it in everyday life because it really is a quantum phenomenon. </p>
<h2>Beyond time crystals</h2>
<p>Quantum computers are still in their infancy. But as they improve they will allow physicists like us to improve our fundamental understanding of nature.</p>
<p>This in turn may translate into technological innovation, just as the physics of the last century enabled the digital revolution that shapes our lives today.</p>
<p>Quantum computers provide a platform for physicists to engineer and investigate novel states of matter that cannot be found in nature. Time crystals just mark the beginning of this exciting endeavour.</p><img src="https://counter.theconversation.com/content/178164/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephan Rachel receives funding from the Australian Research Council (ARC). He is affiliated with the IBM Quantum Hub established at the University of Melbourne.</span></em></p><p class="fine-print"><em><span>Philipp Frey does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Like a coffee you can’t finish stirring, a ‘time crystal’ is a strange quantum state of matter than never settles down to equilibrium.Stephan Rachel, Associate Professor and ARC Future Fellow, The University of MelbournePhilipp Frey, PhD student, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1775562022-02-28T14:31:59Z2022-02-28T14:31:59ZUnpacking a mystery of physics: Why processes in nature operate only in one direction<figure><img src="https://images.theconversation.com/files/447476/original/file-20220221-22-1dfykjy.jpg?ixlib=rb-1.1.0&rect=0%2C343%2C3274%2C2091&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The laws of physics explain why you can't stop ink from spreading in water.</span> <span class="attribution"><span class="source">HAFIZULLAHYATIM/Shutterstock</span></span></figcaption></figure><p>Why do processes in nature only work in one direction? For example, why can’t we heat up a cup of coffee in the fridge or prevent a drop of ink from spreading spontaneously in water?</p>
<p>It’s a question that’s puzzled many generations of physicists – and it stems from an incompatibility in the laws of physics, specifically between those that dictate the behaviour of macroscopic versus microscopic systems. Macroscopic systems can be seen with the naked eye; they consist of an extremely large number of atoms and molecules. Microscopic systems represent a different world: small enough that the behaviour of each individual atom or molecule can be described, but is not visible to our eyes.</p>
<p>Physicists can easily explain why the processes of macroscopic systems can’t reverse themselves spontaneously. It comes down to the <a href="https://www.livescience.com/50941-second-law-thermodynamics.html">second law of thermodynamics</a>, which centres on the nature of the energy of a macroscopic system like a glass of water. This law provides a criterion that predicts the direction of spontaneous processes through the concept of entropy, a measure of order in matter. Liquids are less ordered than crystals, and gases are even less ordered. Hotter or more dispersed matter is higher in entropy. Simply put, entropy always increases; systems become more disordered as they progress spontaneously – and they cannot regress unless we supply energy.</p>
<p>A different set of physical laws exists when looking at the individual atoms and molecules that comprise a microscopic system. But these laws don’t explain what direction the processes in this system must take. </p>
<p>The matter and the processes are the same – but when they are studied from the macroscopic viewpoint the result may contradict that of the microscopic viewpoint. This is of course a problem.</p>
<p>In <a href="https://www.sciencedirect.com/science/article/abs/pii/S0370157321004038?via%3Dihub">our new paper</a> we argue that there’s a solution to this conundrum. The key is to distinguish between two types of reversibility: time-reversibility and thermodynamic reversibility. A smooth transition of the two types would pave the way to a unified theory that can describe all states of matter and all processes based on a single set of principles. This is what scientists are eagerly looking for. </p>
<h2>Equilibrium and gradients</h2>
<p>Consider a pendulum. It swings back and forth indefinitely in the absence of friction. If this motion is recorded and played backwards, there’s no difference; it would still look entirely natural. That’s a time-reversible process – the pendulum’s motion is symmetric with respect to time reversal. </p>
<p>But the heat that is dissipated from a cup of hot coffee never flows back. The heat inevitably flows from the hot coffee into the cooler air and the heat flow stops when the coffee and surrounding air have the same temperature. This final state is called <a href="https://www.britannica.com/science/equilibrium-physics">equilibrium</a>. Since it does not reverse like the pendulum the process is time-irreversible. A recording of it played backwards looks unnatural. This forward direction of processes in nature that stops at equilibrium is famously known as the <a href="http://www.exactlywhatistime.com/physics-of-time/the-arrow-of-time/">arrow of time</a>.</p>
<p>Then there’s thermodynamic reversibility. Heat dissipation is an example: it is driven by a heat gradient, going from warmer to cooler. In fact, all spontaneous processes are driven by some type of gradient – a temperature, concentration, or pressure difference. These processes proceed “downhill” along the gradient, from the higher to lower temperature, higher to lower concentration, or higher to lower pressure. This gradient provides the driving force of the process. Any process in the universe that is driven by some gradient is thermodynamically irreversible. </p>
<p>Gradients govern the course of events in small and large systems. The earth receives energy radiated from the hot surface of the sun and dissipates energy at a much lower temperature into the cold background of the universe. The <a href="https://pubs.rsc.org/en/content/articlelanding/2016/CS/C6CS00115G">processes of life</a> (for plants, animals and humans, among other organisms) are also driven by gradients – their source of energy ultimately comes from the sun in the form of tiny light packets called photons. </p>
<p>All living organisms dissipate energy in the form of colder photons, which is eventually released into outer space. </p>
<h2>Molecular memory</h2>
<p>Time-reversibility doesn’t have anything to do with an entropy gradient. It’s about memory. A process is time-reversible if all the molecules can “remember” where they were and how fast they moved at every instance of time, so that every molecule’s motion can be reversed and the initial state restored. This can be simulated by modern computers if a system isn’t too large. As computer technology advances, increasingly larger and more complex systems can be described at the level of their individual atoms and molecules. </p>
<p>So, the apparent incompatibility between microscopic and macroscopic systems has nothing to do with the size of the system. It has to do with the type of process and whether that process wipes out the molecules’ “memory”.</p>
<p>In the case of heat, or of energy more generally, the same amount of energy that is used to synthesise a sugar molecule is set free when the molecule fuels a process in our body and decays back to its initial constituent molecules. This is the thermodynamic view; it neglects the aspect of time. </p>
<p>If it takes five minutes to synthesise the molecule it does not mean that the molecule also decays after exactly five minutes. We can’t predict the exact time that a molecule will decay because the process of decay is governed by a certain probability per unit time. And, importantly, probabilistic processes are never time-reversible because they contain no memory for the state in earlier times. A complete description of a probabilistic process requires one to take account of both the energetic and the timing aspects. </p>
<p>In this example both the synthesis of the sugar molecules and their decay are thermodynamically irreversible processes because a lot of energy must be added to reverse them. But this is completely different from time reversibility where memory is involved. So in this case, thermodynamic reversibility and time reversibility do not have the same origin. </p>
<p>This is the essence of the problem at hand. It is generally assumed that thermodynamic irreversibility and time irreversibility have the same probabilistic origin, which is often the truth but not always. Our paper argues that these two types of reversibility must be separated.</p><img src="https://counter.theconversation.com/content/177556/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 organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Probabilistic processes are never time-reversible.Tjaart Krüger, Associate Professor in Biophysics, University of PretoriaEmil Roduner, Professor, University of StuttgartLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1767952022-02-13T18:48:51Z2022-02-13T18:48:51ZWe couldn’t have the Beijing Olympics without snow machines. How do they work, and what’s the environmental cost?<figure><img src="https://images.theconversation.com/files/445577/original/file-20220210-1970-2xytwr.jpeg?ixlib=rb-1.1.0&rect=170%2C306%2C7407%2C4737&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Dan Himbrechts/AAP</span></span></figcaption></figure><p>Snow machines have exploited the laws of thermodynamics to paint the slopes of Beijing white for this year’s Winter Olympics.</p>
<p>Beijing might seem like an odd place for the winter games. The city receives almost no annual snowfall and has an <a href="https://en.climate-data.org/asia/china/beijing/beijing-134/">average temperature</a> just below 0°C, even in the winter month of February. </p>
<p>Chinese authorities have used <a href="https://www.technoalpin.com/en/about-us/news/100-technoalpin-olympic-snow">more than 350 snow machines</a> to prepare courses for the world’s athletes. This practice has become more common over the past few Winter Olympics, with the Sochi and Pyeongchang games relying on <a href="https://time.com/6146039/artificial-snow-2022-olympics-beijing/">80% and 98% artificial snow, respectively</a>.</p>
<p>But isn’t all this artificial snow terribly expensive? If you own an air conditioner and keep half an eye on your energy bill, you’d expect snowmaking to be hugely energy-intensive. The uninitiated might think of snow machines as giant freezers with fans attached, guzzling cities’ worth of electricity to refrigerate entire mountainsides.</p>
<p>This isn’t really the case. Efficient machines in suitable climates (such as <a href="https://olympics.com/ioc/news/snow-climate-change-and-the-olympic-winter-games">Beijing’s</a>) can use as little as <a href="https://bioone.org/journals/mountain-research-and-development/volume-31/issue-3/MRD-JOURNAL-D-10-00112.1/Winter-Tourism-and-Climate-Change-in-the-Alps--An/10.1659/MRD-JOURNAL-D-10-00112.1.full">1.5 kilowatt-hours per cubic metre of snow produced</a>. In Beijing’s climate, you could coat a Sydney apartment in a few inches of snow with the same energy the air conditioning would use in an hour.</p>
<p>But that’s not to say there’s no environmental cost. More on that later. </p>
<h2>How do snow machines work?</h2>
<p>Artificial snow is no chemical trick. The slopes of this year’s event are coated in pure frozen water. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/445570/original/file-20220210-27-zii13c.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Snowgun shoots artificial snow towards skiers." src="https://images.theconversation.com/files/445570/original/file-20220210-27-zii13c.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/445570/original/file-20220210-27-zii13c.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/445570/original/file-20220210-27-zii13c.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/445570/original/file-20220210-27-zii13c.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/445570/original/file-20220210-27-zii13c.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/445570/original/file-20220210-27-zii13c.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/445570/original/file-20220210-27-zii13c.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artificial snow is shot out in blower-type machines.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Fundamentally, snow machines work by using a clever thermodynamic exploit, leveraging the natural cooling that happens when water evaporates. And because their cooling power comes from evaporation, they can operate at relatively warm temperatures, up to 1°C (provided the humidity is low enough). </p>
<p>Here’s how it works. Snow machines expel a fine water mist into the cold, dry atmosphere. Some of the water in each droplet quickly evaporates, carrying away heat and lowering the temperature of the rest of the droplet to below its freezing point. This process is known as “evaporative cooling”, and is the same mechanism that cools us when we sweat. </p>
<p>Because the energy loss required to form ice in this process is driven by evaporation, snow machines don’t have to expend energy to <em>freeze</em> water. They only require energy to power the fans and compressors that disperse the water droplets.</p>
<p>However, as any winter Olympian will tell you, snow is more than just frozen water. And snow machines must produce a blanket of powder worthy of the world’s greatest athletes. </p>
<p>They achieve this by using a “nucleator”, which is basically any substance that makes it easier to form an ice crystal. Without this, the droplets in the mist would end up as <a href="https://www.youtube.com/watch?v=_9N-Y2CyYhM">supercooled water</a> and clump into large droplets before freezing. This would create undesirably dense and icy snow.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/_9N-Y2CyYhM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Supercooled water is water which is cooled below freezing point, but which remains liquid because nucleation of the new solid phase is difficult.</span></figcaption>
</figure>
<p>Nucleators can be chemical or biological, but in Beijing <a href="https://olympics.com/ioc/news/snow-climate-change-and-the-olympic-winter-games">no such aids are being used</a>. Instead, tiny ice crystals are being used as nucleators. These nucleator ice crystals themselves are formed by yet more thermodynamic manipulation, wherein pressurised water is forced through a nozzle, quickly reducing the pressure and breaking it into tiny droplets. </p>
<p>When the pressure of a gas is rapidly reduced, its temperature also drops – which is why deodorant from a pressurised spray can feels cold. In this case, the sudden drop in temperature cools the atomised water well below 0°C, rapidly freezing it into the nucleator ice crystals.</p>
<p>In the final step of the snow-making process, these ice crystals mix with the water mist and are propelled through the air, with the water freezing and falling as artificial snow. Propulsion is achieved either through the use of compressed air, in the case of snow lances, or through blower-type machines with large fans.</p>
<p>The snow that forms in this process isn’t quite the same as real snow, because artificial snow forms quickly from liquid droplets, instead of slowly from water vapour. As a result, the shape of artificial snow particles is different to that in natural snow. The former has no beautiful single-crystal structures, only tiny (polycrystalline) snowballs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/445569/original/file-20220210-27-n5rd1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/445569/original/file-20220210-27-n5rd1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/445569/original/file-20220210-27-n5rd1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=218&fit=crop&dpr=1 600w, https://images.theconversation.com/files/445569/original/file-20220210-27-n5rd1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=218&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/445569/original/file-20220210-27-n5rd1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=218&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/445569/original/file-20220210-27-n5rd1.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=273&fit=crop&dpr=1 754w, https://images.theconversation.com/files/445569/original/file-20220210-27-n5rd1.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=273&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/445569/original/file-20220210-27-n5rd1.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=273&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 image on the left shows mostly natural snow crystals with some artificially produced snow underneath, whereas the right shows only snowball shaped artificial snow.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/centers/goddard/news/topstory/2006/olympic_ice.html">Eric Erbe/USDA/NASA</a></span>
</figcaption>
</figure>
<h2>The sustainability question</h2>
<p>As our climate warms and weather patterns shift, we’re becoming increasingly dependent on artificial snow to meet the demands of holidaymakers and sportspeople. These Winter Olympics are the first ever to rely on 100% fake snow. And while snowmaking isn’t as environmentally catastrophic as it might first seem, it’s not without drawbacks.</p>
<p>First, artificial snow is made of water, which is undeniably a critical resource. The International Olympic Committee’s (IOC) sustainability <a href="https://olympics.com/ioc/news/beijing-2022-pre-games-sustainability-report-outlines-climate-solutions-development-of-winter-sports-and-regional-regeneration-in-china">report</a> for this year’s games estimates the city of Zhangjiakou, the epicentre of the Beijing games, will use 730,000m³ of surface water for snowmaking alone (almost 300 Olympic size swimming pools).</p>
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Read more:
<a href="https://theconversation.com/two-thirds-of-earths-land-is-on-pace-to-lose-water-as-the-climate-warms-thats-a-problem-for-people-crops-and-forests-151984">Two-thirds of Earth's land is on pace to lose water as the climate warms – that's a problem for people, crops and forests</a>
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<p>The amount of water used across the entire Beijing area will be much greater (although there are significant efforts to <a href="https://olympics.com/ioc/news/beijing-2022-pre-games-sustainability-report-outlines-climate-solutions-development-of-winter-sports-and-regional-regeneration-in-china">recapture snow melt</a>, and avoid using an excessive amount of drinking water to make snow).</p>
<p>Second, in warmer climates chemical additives are required to help snow form and stay frozen. And while these aren’t actively toxic, there’s still doubt <a href="https://www.acs.org/content/acs/en/education/resources/highschool/chemmatters/past-issues/2018-2019/december-2018/artificial-snow-a-slippery-slope.html">regarding their safety</a>.</p>
<p>Finally, snow machines produce <em>a lot</em> of snow. Early reports from Chinese media claimed <a href="http://www.china.org.cn/sports/2015-07/02/content_35963251.htm">only 200,000m³ of water</a> would be needed for snowmaking. But the <a href="https://olympics.com/ioc/news/beijing-2022-pre-games-sustainability-report-outlines-climate-solutions-development-of-winter-sports-and-regional-regeneration-in-china">IOC’s pre-game report</a> indicates this figure is upwards of 800,000m³. </p>
<p>Depending on which figure is used, the density of the snow created, and how much water is lost to evaporation, the total amount of snow produced could be anywhere from 0.5 to 3 million cubic metres. So while the machines do produce snow efficiently, the total energy usage <a href="https://files.danfoss.com/download/Drives/ITDDPC400A102_TechnoAlpin_LR.pdf">is still significant</a>. </p>
<p>According to the IOC, in Beijing this electricity demand is being met through <a href="https://olympics.com/ioc/news/beijing-2022-pre-games-sustainability-report-outlines-climate-solutions-development-of-winter-sports-and-regional-regeneration-in-china">100% sustainable production</a>. This is encouraging, and will hopefully help accelerate the global adoption of environmentally friendly technologies.</p>
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Read more:
<a href="https://theconversation.com/how-do-olympic-freestyle-skiers-produce-their-amazing-tricks-a-biomechanics-expert-explains-176544">How do Olympic freestyle skiers produce their amazing tricks? A biomechanics expert explains</a>
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<img src="https://counter.theconversation.com/content/176795/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 organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>In Beijing’s climate, you could coat a Sydney apartment in a few inches of snow with the same energy the air conditioning would use in an hour.Chiara Neto, Professor of Physical Chemistry and Australian Research Council Future Fellow, University of SydneyIsaac Gresham, Postdoctral Research Fellow, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1714082021-11-11T14:41:57Z2021-11-11T14:41:57ZCurious Kids: Why does cold air go down and hot air go up?<figure><img src="https://images.theconversation.com/files/430738/original/file-20211108-9897-12uhqlo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The land surface heats up during the day because of solar radiation coming in from the sun.</span> <span class="attribution"><span class="source">Ed Connor/Shutterstock</span></span></figcaption></figure><p><em>Curious Kids is <a href="https://theconversation.com/africa/topics/curious-kids-36782">a series</a> for children in which we ask experts to answer questions from kids.</em></p>
<p><strong>Does cold air go down because the earth’s core is made out of magma and does hot air go up because it’s cold out in space – and does the circle repeat? (Neo, 10, Boksburg, South Africa)</strong></p>
<p>Thank you, Neo, for this great question! You’ve clearly got a very analytical mind, and would make an excellent <a href="https://academickids.com/encyclopedia/index.php/Atmospheric_physics">atmospheric physicist</a> – that’s a researcher who looks at the physical processes happening in our atmosphere – one day. </p>
<p>The rising of hot air and sinking of cool air is important for almost every aspect of our day to day weather and our long term climate. It affects which way the wind blows and how fast it blows. It also affects whether we are likely to have rain, and the type of rainfall. Over larger areas of the earth, and over longer time periods, it even influences our seasons. So this is a really important question, and one which climatologists like myself work on in many aspects of our jobs.</p>
<p>I want to start by describing what’s happening in the earth’s core, then tell you a little bit about the temperature of space. Once I’ve done that, I’ll explain the real reasons hot air rises and cold air sinks.</p>
<h2>The Earth’s core and outer space</h2>
<p>If you were to cut a slice out of the earth, you would see four clear layers. The crust is the thin outer layer – much like an orange skin. The crust is hard, made up of solid rock. It’s the part of the earth that we walk on. Below that is a thicker layer called the mantle; it’s a <a href="https://coolscienceexperimentshq.com/viscosity-of-a-liquid-experiment/">viscous</a> layer of molten (melted) rock. Below that is the outer core, and right at the centre of the earth the inner core. These are very hot layers of molten rock and metal.</p>
<p>And you are quite right –- the earth’s core is <a href="https://www.nationalgeographic.org/encyclopedia/core/">very, very hot</a>. The inner core, made up of iron, is approximately 6,000°C. Even the upper mantle, just below the crust, has an average temperature of 2,000°C. That’s 100 times hotter than most daytime temperatures during spring in South Africa.</p>
<p>But the temperatures at the top of the crust are controlled far more by the sun than by the temperature of the centre of the earth. We’ll come back to that shortly.</p>
<p>Now, let’s talk about the temperature of space.</p>
<p>The earth is surrounded by an atmosphere – a layer of gases that we breathe in and out, and that control our temperatures by absorbing some of the heat, and reflecting the rest. Beyond the atmosphere is what is called “outer space”.</p>
<p>The temperature of outer space just outside the earth’s atmosphere is <a href="https://sciencing.com/temperatures-outer-space-around-earth-20254.html">about 10.17°C</a>. Outer space is heated directly by the sun. The areas in the sun are as warm as 120°C, while areas shaded by the earth are as cold as -100°C. Again, you’re right: this is a lot cooler than the earth’s inner core.</p>
<p>It’s correct that the earth’s core is very hot and space is much cooler. But that’s not the reason hot air rises and cool air sinks. </p>
<h2>Thermodynamics</h2>
<p>To come to the real reason, let’s turn to a field of science called <a href="https://www.britannica.com/science/thermodynamics">thermodynamics</a>. This is the branch of physics which studies heat and energy. Thermodynamics allows us to understand exactly what’s happening to individual bubbles of air. Did you know that the air around us is made of millions and millions of tiny air bubbles that sit very closely together?</p>
<p>Heating of the air can occur via conduction or convection – transferring heat to these air bubbles, and sharing it between them. The land surface heats up during the day because of solar radiation coming in from the sun. This incoming solar radiation is absorbed by the earth, warming it up. It is then released from the earth as long wave radiation, and heats up the air above the ground.</p>
<p>Those air bubbles then move around and bump into each other, sharing their heat between themselves.</p>
<p>When the ground heats up an air bubble above it, that air bubble expands – much like our feet swell up when they’re very hot in our shoes. As the air bubble heats up, the weight of that bubble is spread over a bigger area and so it becomes less dense.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/vSXTBnnx4OA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This is how density works.</span></figcaption>
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<p>As these air bubbles become less dense, they rise because they weigh less than what’s next to them. This is the same when you let go of a helium balloon and it floats away: the helium gas in the balloon is less dense than the air in our atmosphere (which is made up of a large amount of much heavier nitrogen). </p>
<p>The opposite happens when air cools down. The air bubbles contract, their weight takes up much less space and so they become more dense, and sink. This can happen if the air particles move away from the source of heat; they might have risen very high, or moved to an area over a cool lake or over some shade.</p>
<p>So, there’s no link between the earth’s core, space’s temperature and the behaviour of cold air versus hot air. But you definitely think like a scientist, Neo, because you are interested in how one thing influences another. Maybe one day you’ll study thermodynamics, too!</p><img src="https://counter.theconversation.com/content/171408/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jennifer Fitchett receives funding from the DSI-NRF Centre of Excellence (GENUS). </span></em></p>This is a really important question, and one which climatologists work on in many aspects of their jobs.Jennifer Fitchett, Associate Professor of Physical Geography, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1445662021-03-18T19:01:48Z2021-03-18T19:01:48ZCurious Kids: how do freezers work?<figure><img src="https://images.theconversation.com/files/388723/original/file-20210310-23-xt7gt6.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3872%2C2585&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p><strong>How does the freezer work? — Leon, aged 4</strong></p>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>Hi Leon,</p>
<p>That’s a great question! But freezers are a bit tricky to explain, so we’ll need to talk about a few other things first.</p>
<p>Everything you can touch and feel (like air, water, rocks and mice) is made of tiny balls called <em>atoms</em>. When atoms join up into small groups moving around together, they are called <em>molecules</em>. Atoms and molecules are too small to see without very powerful microscopes.</p>
<h2>Solids, liquids and gases</h2>
<p>Most things come in three <em>phases</em>: solid, liquid or gas. Think of ice, water and steam. If a gas is not too hot, we can also call it <em>vapour</em>. (There are other phases too, but let’s ignore them for today.)</p>
<p>In solids (like ice), atoms or molecules are tightly stuck together and can barely move. They are usually lined up in neat rows called <em>crystals</em>. In liquids (like water) atoms or molecules are loosely stuck close together, but can move around. In a gas (like steam), atoms or molecules are far apart and free to float away from each other.</p>
<p>Most gases, including air, are made of small molecules. Some gases (like the helium inside floating party balloons) are made of single atoms moving around on their own.</p>
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<img alt="" src="https://images.theconversation.com/files/388238/original/file-20210308-15-1jy831a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/388238/original/file-20210308-15-1jy831a.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=487&fit=crop&dpr=1 600w, https://images.theconversation.com/files/388238/original/file-20210308-15-1jy831a.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=487&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/388238/original/file-20210308-15-1jy831a.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=487&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/388238/original/file-20210308-15-1jy831a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=612&fit=crop&dpr=1 754w, https://images.theconversation.com/files/388238/original/file-20210308-15-1jy831a.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=612&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/388238/original/file-20210308-15-1jy831a.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=612&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">A solid melts into a liquid then evaporates into a gas (or vapour)</span>
<span class="attribution"><span class="source">Stephen G Bosi</span></span>
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<p>If I heat up a solid, the atoms or molecules start to bounce a little bit, but they still stay stuck in their neat rows. Now, if I add an extra burst of heat, the solid turns into liquid. This means the atoms and molecules bounce around so hard they start to move around, breaking up those neat rows. Although the atoms can now flow around, they still stay very close together. This is what’s happening if you put an ice block in a bowl and watch it slowly melt into water.</p>
<p>To turn a liquid into a gas (or vapour), the atoms and molecules must break away completely from their neighbours. This takes another extra burst of heat to give the atoms and molecules a kick to rip them away from their sticky neighbours and float away. (Scientists call this extra burst of heat <em>latent heat</em>.) </p>
<p>This is what happens when you put water into a kettle, turn on the heat, and watch the steam floating out of the spout.</p>
<p>These atoms or molecules carry that extra burst of heat away with them when they float away. This is why your face feels cooler if the wind turns your sweat into vapour and floats away from your face.</p>
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Read more:
<a href="https://theconversation.com/curious-kids-why-can-some-cups-go-in-the-microwave-and-some-not-82831">Curious Kids: Why can some cups go in the microwave and some not?</a>
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<p>OK. Now let’s try it <em>backwards</em>. If you take enough heat out of a vapour (like steam), it will turn back into a liquid (like water). Whenever this happens, the vapour brings the extra burst of heat back into the liquid.</p>
<p>Now, finally, I can explain how your freezer works.</p>
<h2>How the freezer works… at last!</h2>
<p>Hidden inside the walls of your freezer is a curly metal tube called a cooling pipe. It is full of a special liquid that evaporates easily. </p>
<p>The cooling pipe is connected to a pump that sucks in vapour from the cooling pipe. The sucking makes more liquid turn to vapour, and when that happens it takes some heat out of the freezer. Just like sweat floating away cools your face down, this vapour floating away makes the inside of the freezer cool down.</p>
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<img alt="" src="https://images.theconversation.com/files/388239/original/file-20210308-13-139tnur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/388239/original/file-20210308-13-139tnur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=287&fit=crop&dpr=1 600w, https://images.theconversation.com/files/388239/original/file-20210308-13-139tnur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=287&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/388239/original/file-20210308-13-139tnur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=287&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/388239/original/file-20210308-13-139tnur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=361&fit=crop&dpr=1 754w, https://images.theconversation.com/files/388239/original/file-20210308-13-139tnur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=361&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/388239/original/file-20210308-13-139tnur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=361&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">The cooling system inside a freezer.</span>
<span class="attribution"><span class="source">Stephen G Bosi</span></span>
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<p>Next, the pump takes vapour from the cooling pipe and squeezes it into another curly pipe on the outside of the back of the fridge. When the pump squeezes the vapour, it pushes the molecules closer together so they start to stick together and turn into a liquid again.</p>
<p>When the gas turns back into a liquid, it gives off the latent heat energy it took from the freezer. So the pipe on the back of the fridge gets warm, and the heat escapes into the air in your kitchen.</p>
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Read more:
<a href="https://theconversation.com/curious-kids-how-does-heat-travel-through-space-if-space-is-a-vacuum-111889">Curious Kids: how does heat travel through space if space is a vacuum?</a>
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<p>In other words, the pump moves heat from inside your freezer and lets it go into your kitchen, making the freezer colder and your kitchen warmer. If you feel the back and sides of your fridge, they should feel a bit warm. That’s the heat that used to be inside your freezer!</p>
<p>After releasing its heat energy, the liquid leaks through a little skinny pipe back into the cooling pipe where it started. Then the sucking from the pump turns it into gas again, and the whole cycle repeats over and over. And that’s what keeps your freezer cold.</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 curiouskids@theconversation.edu.au</em></p><img src="https://counter.theconversation.com/content/144566/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephen G Bosi does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Freezers use a evaporation and condensation to pump heat out of the fridge and into the kitchen.Stephen G Bosi, Senior Lecturer in Physics, University of New EnglandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/983672018-07-24T10:27:01Z2018-07-24T10:27:01ZWhy does my phone battery die so fast?<figure><img src="https://images.theconversation.com/files/228292/original/file-20180718-142428-m8rlfk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Already out of charge – again?!</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/portrait-young-angry-woman-holding-cellphone-521627047">fizkes/Shutterstock.com</a></span></figcaption></figure><p>Why do batteries die? And, why can they only be recharged so many times before they won’t hold a useful amount of charge? My young son asked me about that years ago when his battery-powered toy car stopped moving, wondering about what he called an “everlasting battery.” And this same question has probably crossed the mind of every cellphone user trying to send one last text before the screen blinks off.</p>
<p><a href="https://scholar.google.com/citations?user=LYNGYrgAAAAJ&hl=en">Research, like mine</a>, <a href="https://doi.org/10.1142/9487">continues around the world</a> to make batteries that charge faster, last longer, and can be recharged and discharged many more times than today’s. But as much as you and I would like, it’s impossible to make a truly everlasting battery. I have taught thermodynamics for more than 30 years. So far, there is nothing that suggests we can break the fundamental laws of science to get that elusive battery.</p>
<p>Battery scientists and engineers call the main problem “capacity fade.” Regular people wonder about it with questions like “Why won’t my battery hold a charge?” and complaints like “I just recharged this thing and it’s already out again!” </p>
<p>It’s a result of the <a href="https://www.grc.nasa.gov/WWW/k-12/airplane/thermo2.html">second law of thermodynamics</a>, which states that whenever some real process happens, it creates a certain amount of wasted energy along the way that can never be recovered. Any time a battery is charged or discharged, there’s a little bit of wasted energy – a little bit of wasted capacity in the battery that cannot be recovered.</p>
<p>To envision how this works, think about battery use like transferring water between two cups. Using a battery is like emptying the water from one cup into the other, and charging the battery involves pouring the water back into the first cup. Even if you do it one or two times without spilling a drop, there’s always just a little tiny bit left in each cup that you can’t pour out.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/pVbaRYoSBYk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">There’s always at least a little left over.</span></figcaption>
</figure>
<p>Now imagine pouring back and forth hundreds or even thousands of times over a period of two or three years (for a cellphone battery) or 10 to 20 years (for an electric car). Over time, all the thousands of little and big things that go wrong add up to quite a bit of water going missing. Even spilling a barely visible drop – say one-tenth of a milliliter – adds up to an entire liter if it happens 10,000 times. That doesn’t even include the possibility of one cup failing in some way that loses even more water – like springing a leak or heating up and causing evaporation.</p>
<p>Just as water inevitably goes missing when pouring from one cup to another, more energy is required to charge the battery than it actually stores, and less energy comes out than is stored in it. The proportion of wasted energy to stored energy grows over time.</p>
<p>In fact, the more you use a battery, the more energy gets wasted, and the sooner the battery will reach a point where it’s dead and can’t usefully be recharged. I and others are <a href="https://doi.org/10.1142/9789814651905_0014">studying ways to have those discharging-recharging cycles run more smoothly</a> to reduce the amount of waste, but the second law of thermodynamics will always make sure that there’s no way to get rid of it entirely.</p><img src="https://counter.theconversation.com/content/98367/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Steve W. Martin 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>Emptying and refilling a battery is a lot like pouring water from one glass to another, over and over again.Steve W. Martin, Professor of Materials Science and Engineering, Iowa State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/807952017-08-03T00:59:51Z2017-08-03T00:59:51ZHow hot weather – and climate change – affect airline flights<figure><img src="https://images.theconversation.com/files/180077/original/file-20170727-8486-3gcmgf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When is it too hot to fly?</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/heat-wave-airplane-airport-665107561">Dmitri Fedorov/Shutterstock.com</a></span></figcaption></figure><p>Hot weather has forced <a href="https://www.washingtonpost.com/news/capital-weather-gang/wp/2017/06/20/its-so-hot-in-phoenix-that-airplanes-cant-fly/">dozens of commercial flights to be canceled</a> at airports in the Southwest this summer. This flight-disrupting heat is a warning sign. Climate change is projected to have far-reaching repercussions – including <a href="http://dx.doi.org/10.1098/rsta.2012.0294">sea level rise inundating cities</a> and shifting weather patterns causing <a href="http://dx.doi.org/10.1073/pnas.0906865106">long-term declines in agricultural yields</a>. And there is evidence that it is beginning to affect the takeoff performance of commercial aircraft, with potential effects on airline costs.</p>
<p>National and global transportation systems and the economic activity they support have been <a href="http://dx.doi.org/10.1038/nature15725">optimized for the climate</a> in which it all developed: Machines are designed to operate in common temperature ranges, logistical plans depend on historical weather patterns and coastal land development is based on <a href="http://cpo.noaa.gov/sites/cpo/Reports/2012/NOAA_SLR_r3.pdf">known flood zones</a>. In the aviation sector, airports and aircraft are designed for the weather conditions experienced historically. Because the climate is changing, even fundamental infrastructure elements like airports and key economic sectors like air transportation may need to be redesigned and reengineered.</p>
<p>As scientists focused on the <a href="http://dx.doi.org/10.1175/WCAS-D-15-0063.1">impacts of climate change and extreme weather</a> on human society and natural ecosystems around the world, our research has quantified how extreme heat associated with our <a href="http://dx.doi.org/10.1007/s10584-017-2018-9">warming climate may affect flights</a> around the world. We’ve found that major airports from New York to Dubai to Bangkok will see more frequent takeoff weight restrictions in the coming decades due to increasingly common hot temperatures.</p>
<h2>Climate changes flights</h2>
<p>There is robust evidence that extreme events such as heat waves and coastal flooding are happening with <a href="http://dx.doi.org/10.1073/pnas.1222469111">greater frequency and intensity</a> than just a few decades ago. And if we fail to reduce greenhouse gas emissions significantly in the next few decades, the frequency and intensity of these extremes is projected to <a href="http://dx.doi.org/10.1002/jgrd.50188">increase dramatically</a>. </p>
<p>The effects on aviation may be widespread. Many airports are built near sea level, putting them <a href="https://doi.org/10.1016/j.trpro.2016.05.036">at risk of more frequent flooding</a> as oceans rise. The frequency and intensity of <a href="http://dx.doi.org/10.1038/nclimate1866">air turbulence may increase</a> in some regions due to <a href="http://dx.doi.org/10.1007/s00376-017-6268-2">strengthening high-altitude winds</a>. Stronger winds would force airlines and pilots to <a href="https://doi.org/10.1088/1748-9326/11/2/024008">modify flight lengths and routings</a>, potentially increasing fuel consumption. </p>
<p>The July heat-related <a href="https://www.circa.com/story/2017/06/20/nation/american-airlines-canceled-flights-in-phoenix-because-its-too-hot-for-planes-to-fly">Phoenix flight cancellations</a> happened at least in part because airlines’ operational manuals didn’t include information for <a href="http://www.fox10phoenix.com/news/arizona-news/262509476-story">temperatures above 118 degrees Fahrenheit</a> – because that kind of heat is historically uncommon. It’s another example of how procedures may need to be updated to adapt to a warmer climate.</p>
<h2>Flying in the heat</h2>
<p>High air temperatures affect the physics of how aircraft fly, meaning aircraft takeoff performance can be <a href="https://doi.org/10.1175/WCAS-D-14-00026.1">impaired on hot days</a>. The amount of lift that an airplane wing generates is affected by the density of the air. Air density in turn depends mostly on air temperature and elevation; higher temperatures and higher elevations both reduce density. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=874&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=874&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=874&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1098&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1098&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1098&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hot air is less dense than cooler air. That affects the amount of lift an airplane can generate.</span>
<span class="attribution"><span class="source">The Conversation (via Piktochart)</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The lower the air density, the faster an airplane must travel to produce enough lift to take off. It takes more runway to reach a higher speed, and depending on how long the airport’s runway is, some airplanes might risk running out of room before reaching sufficient speed. When this occurs, the only immediate option is to reduce the aircraft’s weight to lower its required takeoff speed – by removing passengers, luggage and cargo. This is referred to as a weight restriction. </p>
<p>Weight restrictions happen now, especially in hot places like Phoenix and <a href="http://www.ldeo.columbia.edu/news-events/surging-heat-may-limit-aircraft-takeoffs-globally">Dubai</a> and at airports with short runways like <a href="https://www.wsj.com/articles/la-guardias-runways-come-up-short-1479078957">New York’s LaGuardia</a> and Washington, D.C.’s Reagan National, but our research suggests that they may become much more common in the future. </p>
<p>Global temperatures have been <a href="https://www.ipcc.ch/report/ar5/wg1/">steadily rising for decades</a>, and they will almost certainly continue to do so. In some regions, there is evidence that the <a href="http://dx.doi.org/10.1002/2015GL064914">hottest temperatures may increase at a faster rate</a> than the average, <a href="http://dx.doi.org/10.1007/s40641-016-0042-x">further stacking the deck</a> in favor of extreme heat. These hotter temperatures will reduce air density and make it much more likely weight restrictions are needed for flights taking off during the hottest parts of the day. </p>
<p>The frequency and magnitude of weight restrictions is projected to increase – in some locations, the number of days requiring at least some amount of weight restriction for certain aircraft could double or triple, perhaps covering 50 or more days per year.</p>
<h2>The economics of adaptation</h2>
<p>On most affected flights, the amount of cargo, passengers and fuel that must be removed to allow for takeoff will usually be small – between 0.5 percent and 4 percent of the total load. That means fewer paying customers on airplanes, and less cargo on board. When those restrictions add up across the global air transport system, the costs can be significant.</p>
<p>Carrying just a fraction of a percent fewer passengers or less cargo can add up to <a href="https://www.wired.com/2012/09/how-can-airlines-reduce-fuel-costs/">millions of dollars in lost revenue</a> for an airline over years of operation. That makes even small weight restrictions a concern in such a highly competitive and optimized industry. These limits could disproportionately affect <a href="https://www.ft.com/content/689a1618-814d-11e5-8095-ed1a37d1e096">long-haul flights</a>, which require large fuel loads and often take off near their maximum weights.</p>
<p>There are ways that airlines could mitigate increasing weight restrictions. The most feasible is to reschedule some flights to cooler hours of the day – although with <a href="http://www.iata.org/pressroom/pr/Pages/2016-10-18-02.aspx">air traffic increasing</a> and many airports already <a href="http://www.accessmagazine.org/spring-2016/manage-flight-demand-or-build-airport-capacity/">operating near capacity</a>, this could prove difficult. </p>
<p>Another potential solution is to build longer runways. But that’s not always possible: Some airports, like New York’s LaGuardia, are on coastlines or in dense urban environments. Even where a longer runway is technically possible, buying the land and expanding an airport’s physical area may be <a href="http://www.bbc.com/news/business-35011620">expensive and politically difficult</a>.</p>
<p>Aircraft could be optimized for takeoff performance, but redesigning aircraft is <a href="http://www.seattletimes.com/business/boeing-aerospace/will-787-program-ever-show-an-overall-profit-analysts-grow-more-skeptical/">extremely expensive and can take decades</a>. <a href="http://www.boeing.com/features/2016/01/innovation-777-lighter-01-16.page">Manufacturers are always working</a> to build planes that are <a href="https://www.wired.com/2015/06/planes-get-efficient-heres/">lighter and more fuel-efficient</a>. In the future, those efficiency improvements will be necessary just to maintain today’s performance.</p>
<h2>Broader implications</h2>
<p>These changes are merely examples of the countless procedures, processes and equipment requirements that will have to be adjusted for a changing climate. Even if those adaptations are successful, they will take effort and money to achieve.</p>
<p>Many sectors of the economy, including the aviation industry, have yet to seriously consider the effects of climate change. The sooner, the better: Both airport construction and aircraft design take decades, and have lasting effects. Today’s newest planes may well be <a href="http://www.airspacemag.com/need-to-know/what-determines-an-airplanes-lifespan-29533465/">flying in 40 or 50 years</a>, and their replacements are being designed now. The earlier climate impacts are understood and appreciated, the more effective and less costly adaptations can be. Those adaptations may even include innovative ways to dramatically reduce climate-altering emissions across the aviation sector, which would help reduce the problem while also responding to it.</p><img src="https://counter.theconversation.com/content/80795/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>Major airports around the world will see more frequent flight restrictions in the coming decades because of increasingly common hot temperatures.Ethan D. Coffel, Ph.D. Student in Earth & Environmental Sciences, Columbia UniversityRadley Horton, Associate Research Scientist, Center for Climate Systems Research, Columbia UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/533262016-02-02T12:13:44Z2016-02-02T12:13:44ZConfessions of a chemist: I make molecules that shouldn’t exist<figure><img src="https://images.theconversation.com/files/109799/original/image-20160201-32237-1bof9wc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Shaken not stirred ...</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-324857183/stock-photo-concept-of-chemistry-bookshelf-full-of-books-in-form-of-test-tube-with-chemistry-draw-on.html?src=pd-same_artist-322807478-gmrzSV2APiEo3bGPtztxxA-4">StudioVin</a></span></figcaption></figure><p>At drinks parties and dinners, if someone asks what I do for a living, I always say: “Synthetic chemist … I make new molecules … especially those that shouldn’t exist.” People typically respond that they were not very good at chemistry at school – or they enquire about explosions and smells. And there, usually, the conversation ends.</p>
<p>I worry that chemists are missing a self-promotion trick. While physicists can argue the need to understand the fundamental nature of the universe by studying subatomic particles at the <a href="http://home.cern/topics/large-hadron-collider">Large Hadron Collider</a>, we chemists beaver away using and developing fundamental knowledge of how to connect molecules together. We routinely have to overcome basic <a href="https://www.khanacademy.org/science/chemistry/thermodynamics-chemistry">thermodynamics</a>, which would stop any of us from existing if they controlled the universe – the building blocks of life would simply end up as carbon dioxide, water and ammonia. </p>
<p>I suspect chemistry’s problem is that much of it is just too useful and everyday – though not all of it, as we shall see. Chemistry tends to have recognisable applications such as making drugs, paints, plastic, synthetic fibres and electronics. The Hadron Collider, on the other hand, benefits from looking spectacular and performing abstract feats that’s appeal lies in their distance from the world that we know. </p>
<h2>My work</h2>
<p>For the past 40 years, I have worked on the chemistry of the heavier <a href="http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_16%3A_The_Oxygen_Family/1Group_16%3A_General_Properties_and_Reactions">group 16 elements</a>, including sulphur, selenium and tellurium. These have always fascinated me – in part, because the reaction chemistry is quite unpredictable. My early work was on sulphur-nitrogen compounds. Sulphur and nitrogen are quite unusual in that they both exist in nature as their basic elements. With some ingenuity it is possible to form simple compounds containing only them – a classic case of overcoming the thermodynamics that are responsible for the elements being “stable”. </p>
<p>One example is tetrasulphur tetranitride (S<sub>4</sub>N<sub>4</sub>), an orange solid with an interesting cage structure which was first made 180 years ago. The compound is perfectly stable – at least unless there is a tiny bit of heat from friction. That makes it explode violently to give sulphur and nitrogen as thermodynamics takes over. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/109805/original/image-20160201-32222-znh2ym.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/109805/original/image-20160201-32222-znh2ym.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/109805/original/image-20160201-32222-znh2ym.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=629&fit=crop&dpr=1 600w, https://images.theconversation.com/files/109805/original/image-20160201-32222-znh2ym.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=629&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/109805/original/image-20160201-32222-znh2ym.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=629&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/109805/original/image-20160201-32222-znh2ym.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=791&fit=crop&dpr=1 754w, https://images.theconversation.com/files/109805/original/image-20160201-32222-znh2ym.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=791&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/109805/original/image-20160201-32222-znh2ym.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=791&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">OLED on display.</span>
<span class="attribution"><a class="source" href="https://www.google.co.uk/search?client=safari&channel=mac_bm&hl=en&site=imghp&tbm=isch&source=hp&biw=1440&bih=752&q=OLED+television&oq=OLED+television&gs_l=img.3..0j0i24l8.1086.2546.0.2950.15.12.0.0.0.0.99.539.9.9.0....0...1ac.1.64.img..6.9.536.EphRXH1UhKM#q=OLED+television&channel=mac_bm&hl=en&tbm=isch&tbs=sur:fc&imgrc=HEM0D6CLA8yKCM%3A">LG</a></span>
</figcaption>
</figure>
<p>One of the main uses of tetrasulphur tetranitride is as a precursor to creating other sulphur-nitrogen compounds. It can be used, for instance, to prepare a longer chain-like molecule known as a polymer. This is truly alchemy. Known to chemists as polythiazyl, it looks metallic and golden and conducts electricity. </p>
<p>Polythiazyl was in fact the first non-metal material to be <a href="http://pubs.acs.org/doi/abs/10.1021/cr60317a002">found to be</a> a superconductor at low temperatures. This discovery was partly responsible for the whole era of <a href="http://www.colae.eu/what-is-organic-electronics/">organic electronic materials</a>, which apart from winning a <a href="http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2000/">Nobel Prize</a> has given us the likes of <a href="http://www.whathifi.com/news/oled-tv-everything-you-need-to-know">OLED televisions</a>, which need no back light and can therefore be thinner and lighter than other televisions. How ingenious is the synthetic chemist to take two stable highly abundant elements and prepare a simple compound that otherwise would not exist? </p>
<h2>Phosphorus and tellurium</h2>
<p>My group has also worked on phosphorus-sulphur chemistry, which is important in the additives that keep engine oil from turning into tar; and phosphorus-selenium chemistry, which is behind glass-like semiconductors – these might have applications in solar cells in the longer term. <a href="http://onlinelibrary.wiley.com/doi/10.1002/chem.201303884/abstract">Most recently</a> we have been trying to make simple compounds that bond together phosphorus and tellurium (known as P-Te bonds). This is a stupidly hard thing to do. The customary wisdom is that because tellurium is metallic, simple P-Te bonds are bound to simply break and leave you with tellurium metal. To demonstrate otherwise, it took three groups working together in Canada, Germany and the UK. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/109806/original/image-20160201-32254-mqfud4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/109806/original/image-20160201-32254-mqfud4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/109806/original/image-20160201-32254-mqfud4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/109806/original/image-20160201-32254-mqfud4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/109806/original/image-20160201-32254-mqfud4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/109806/original/image-20160201-32254-mqfud4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/109806/original/image-20160201-32254-mqfud4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/109806/original/image-20160201-32254-mqfud4.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">The building blocks of life.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/wolframburner/3751529776/in/photolist-spwVNd-spEeNt-6Hvz6S-4jLz3a-tKiNaS-2vQ2RQ-2vVkpu-uzBhpK-xWzRQH-w7K35w-yeLnkp-uzBhzp-sFW7z5-spwTqC-sG7n18-Anw2Ep-5dY78J-4sAnt2-9HA7tv-bcG9pV-9HiftY-6uDAoL-6uzorT-dWUQsG-6uDAa3-vbnnqf-vbnkqU-w2JjMf-osfrbr-oaKMdN-osfrjH-yd9U6S-bmMReq-w4zCGq-bx899i-scRSQ6-w5bPcM-v8aYqh-9jB4m7-w5AbQ6-e49fLS-nwjpaf-dWUMvJ">Wolfram Burner</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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</figure>
<p>I cannot envisage any ready practical application for such compounds, but that certainly doesn’t make it pointless. Learning how to manipulate the structure to stabilise a P-Te bond gives us a fundamental understanding of the forces that hold molecules together and the reaction pathways that can be employed, which is transferable to other problems in chemistry such as making stable materials for the electronics industry. </p>
<p>Along the way we developed new routes to involve certain chemicals in the process. These may prove very valuable for others working in more applied areas (it’s hard to predict what these might be). We learned that an unlikely bond is perfectly possible and can be created in compounds that can be weighed out and put on the shelf. It was also a challenging project for the PhD student who did most of the work.</p>
<p>If you want to understand the art and science of chemistry, this sort of work sums it up – making molecules that shouldn’t exist. It may not lay claim to answering life’s big questions in the same way as physics, but we are still talking about explorations in science that often benefit us in more ways than we can predict. When it comes down to it, the two disciplines are really not so different. </p>
<p>As for my team, now that we have shown what can be done with phosphorus and tellurium, we are wondering: where next? Arsenic-tellurium compounds are even more challenging, so watch this space.</p><img src="https://counter.theconversation.com/content/53326/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Derek Woollins receives funding from the Leverhulme Foundation and EPSRC.</span></em></p>Getting tellurium and phosphorus to form a molecule is stupidly hard and not very glamorous. Here’s why it’s worth the effort.Derek Woollins, Vice Principal (Research) and Provost, University of St AndrewsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/195752013-10-29T14:56:57Z2013-10-29T14:56:57ZIt’s no reverse microwave, but it is cool<figure><img src="https://images.theconversation.com/files/34028/original/q6422cwn-1383055798.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Better than your refrigerator</span> <span class="attribution"><span class="source">Eco-Cool</span></span></figcaption></figure><p>How can you turn lukewarm lager to ice-cold beer in under a minute? A startup has developed a nifty gizmo which does just that, saving both energy and embarrassment at parties. Manufacturer Enviro-Cool <a href="http://www.enviro-cool.co.uk/technical-information/">claims</a> that chilling on demand with a V-Tex could save retailers €1000 per fridge per year, and of course help to keep the planet cool too. So how does the device actually work?</p>
<p>Media reports have dubbed the device a “<a href="http://www.telegraph.co.uk/science/science-news/10404692/Reverse-microwave-can-chill-wine-bottles-and-fizzy-drink-cans-in-45-seconds.html">reverse microwave</a>”, but that analogy would receive a chilly reception amongst physicists. Unfortunately, you can’t simply wire up a microwave oven backwards and suck the heat from an object. </p>
<p>In fact, despite the PR spin about “Rankine vortices”, this device is remarkably unremarkable in some respects: the rapid cooling of drinks is achieved by putting them into contact with something cold. However, there is a twist: the interesting science here is fluid dynamics, not thermodynamics.</p>
<h2>Tricky chilling</h2>
<p>It’s easy to heat food quickly in a microwave oven. Why is it so hard to cool things down? The temperature of an object is essentially a measure of how much energy it holds. A hotter object has more energy than a colder one. Cooling is difficult because coaxing the atoms inside an object to give up their energy is a tricky business. </p>
<p>If you want to cool a material at will, you need to choose your material quite carefully. A gas is ideal: gases can be heated by compression (which is why a bicycle pump is warm to the touch after use) or, conversely, cooled by expansion (which is why the rapidly-expanding gas from an aerosol can feels cool).</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/34024/original/vntkwsh8-1383049679.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/34024/original/vntkwsh8-1383049679.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/34024/original/vntkwsh8-1383049679.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/34024/original/vntkwsh8-1383049679.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/34024/original/vntkwsh8-1383049679.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/34024/original/vntkwsh8-1383049679.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/34024/original/vntkwsh8-1383049679.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Chilled in a few seconds.</span>
<span class="attribution"><span class="source">Eco-Cool</span></span>
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<p>There are no gaseous foods, and solids or liquids are more difficult to chill. The only simple option is to place them in contact with something cold.</p>
<p>This is, of course, how a fridge works: compressing and expanding gas in a series of tubes makes them cold. These tubes then cool the air in the fridge, which then cools your food. The problem with this process is that air and food are pretty terrible conductors of heat, so it takes a long time for the heat to flow out of food, via the air and into the cold pipes, where it is expelled from the back of the fridge to warm up the kitchen.</p>
<p>Thus, to increase the speed of cooling, we need another medium to transport heat. This is the first aspect of the V-Tex which differs from a normal fridge: it uses water to carry the heat from the drink being cooled. But water is so much more effective than air that you run into another problem. Suck out heat from a chicken too quickly and the skin will be frozen before the inside even begins to cool—the opposite of a typical barbecue disaster where food cooked at too high a heat is burnt on the outside, but still raw on the inside. In the case of drinks, the nonuniform cooling can create either an exterior layer of ice with a highly concentrated solution of icky syrup at its core, or an unintentional slushie of half-frozen Sauvignon blanc.</p>
<p>With solid objects, from last night’s pasta bake to <a href="http://www.thenakedscientists.com/HTML/content/interviews/interview/1802/">organs for transplant</a>, this is where the story ends: you are just going to have to cool it more carefully if you want to avoid freezing. But with a liquid, you have another option: agitate the liquid such that the whole volume is uniformly exposed to the cold.</p>
<h2>Twisted problem</h2>
<p>Many common beverages, however, pose one further problem. From Pepsi to Prosecco, the fizz in fizzy drinks comes from CO<sub>2</sub> gas dissolved in the liquid. This CO<sub>2</sub> is looking for any excuse to escape, and these excuses come in the form of “nucleation sites”, which encourage bubbles to form: from <a href="http://www.youtube.com/watch?v=hKoB0MHVBvM">tiny pits on the surface of Mentos</a> to a disturbance in the liquid itself. This is why you can’t simply shake ’n’ cool: if you’ve ever played a playground prank with a shaken bottle of Coke, or watched champagne being sprayed from a Formula One podium, you’ll be aware of the effervescent consequences of disturbing a liquid containing dissolved gas.</p>
<p>This is why the V-Tex designers had to devise a smart way of uniformly cooling fizzy liquids. The solution was to rotate, shake with a wiggle and rotate again. This creates a smooth-flowing vortex, with no pressure waves which might induce bubble formation. Details are scant (patents cover the meticulous choreography behind it), but the website does <a href="http://www.enviro-cool.co.uk/ip/">mention</a> repeated creation and destruction of a “Rankine vortex”, which is one way in which a fluid can smoothly swirl.</p>
<p>This device is no reverse microwave: its rapid cooling only works on liquids, and the thermal conduction of the container makes a significant difference (<a href="http://www.enviro-cool.co.uk/cooling-times/">they claim</a> a 500 ml metal can can be cooled in 50 seconds and an equivalent glass bottle would take six minutes).</p>
<p>The media missed out on a better story: in a V-Tex your drink is being stirred, not shaken, by a rapidly moving robot arm (in a tank of ice water). Make the whole assembly transparent and throw in some LEDs, a little more like <a href="http://www.enviro-cool.co.uk/prototype-gallery/">the prototype</a>, and the short wait for your fizzy pop lays bare some cool physics.</p><img src="https://counter.theconversation.com/content/19575/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Steele does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>How can you turn lukewarm lager to ice-cold beer in under a minute? A startup has developed a nifty gizmo which does just that, saving both energy and embarrassment at parties. Manufacturer Enviro-Cool…Andrew Steele, Bioinformatician, King's College LondonLicensed as Creative Commons – attribution, no derivatives.