The international prototype kilogram keeps changing weight so scientists have come up with a new way to calculate.
To stay up, the bird must overcome gravity with a force called 'lift'.
Imagine the Earth pulling everything it is made up of, all of its mass, towards its centre. This happens evenly all over the Earth, causing it to take on a round shape.
We talk about mass all the time but what is it that actually gives an object mass? And why do some things have mass and others have no mass at all?
The Nobel Prize-winning research on neutrinos is expected to push the boundaries of science and technology.