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Asked by megansaurus to Davie, Gemma, James P, James V, Nuala on 27 Jun 2012.
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Nuala Carson answered on 27 Jun 2012:
Hey megansaurus,
This is a great question! Its pretty complicated but i will attempt to explain my understanding of it. So when the big bang occurred there were lots of bits of rock and fragments formed. These were all spinning as they were thrown away from the point of creation. The earth formed when lots of these little fragments clumped together.
The fact that the earth is still spinning is all to do with what we refer to as the ‘conservation of angular momentum’. Angular momentum is how fast something spins round an axis (so like the earth). This sounds pretty complex but you can feel its effect pretty simply. If you think of an ice skater spinning round, if she pulls her legs and arms in she spins faster. That happens because physics states that we have to conserve angular momentum. when the earth formed it had to conserve the angular momentum of all the little fragments.
The rotation of the earth gives us night and day so its pretty cool. I think there is a theory that the earth’s spin is actually slowing down?
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James Verdon answered on 27 Jun 2012:
Hi megansaurus,
When the sun formed, there was a bit of debris still orbiting around it. The debris was what became the planets (the sun is 98% of the solar system, so we really are little bits of leftovers compared to the sun). Gradually, this debris came together under the force of gravity to form the planets we know today.
Because the debris was spinning around the sun the planets, when they were formed, were spinning as well. The spinning would have sped up when the planets came together, because as they collapsed to become planets, you have this ice-skater effect that Nuala mentioned. As the planet gets smaller, it spins faster.
Once they started spinning, there is nothing to stop them spinning. There is no air-resistance in space, so once something is spinning it will keep spinning forever unless something acts to slow it down.
However, the earth is spinning a little bit more slowly every year. This is because of the tides we see every day. The movement of the moon around the earth makes the seas on our planet move up and down. The energy needed to do this comes from the earth’s rotation, so the spin is reduced slightly. This is a really small effect though, so every 100 years days get longer by 0.002 seconds.
A side effect of this is that gravitational energy is transferred to the moon, which speeds up its orbit. This makes it move slightly further away from the earth. So the moon is (very) gradually moving away while we slow down. And all because we have tides.
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James Pope answered on 27 Jun 2012:
Hi megansaurus,
Can’t add anything to Nuala and James V’s answers, their brilliant, but I do have an interesting climate fact from the rotation!
The Earth spins around an axis, which is slightly tilted in one direction. This tilt is responsible for our seasons of the year with summer and longer days when our tilt has us leaning towards the sun and winter & shorter days when it has us leaning away.
The angle tilt is also really important for longer term climate changes, called Obliquity it changes on a regular cycle between two end points and it is one of the Milankovitch forcings are cycles found to have caused the glacial/inter-glacial cycles of the ice ages. If the angle increases, then summers get more solar energy and it is harder for ice sheets to form, if the angle decreases then the opposite occurs. The angle changes on a cycle of 40,000 years from one extreme to the other and back again, and it dominated the climate from about 5 million to 1.8 million years ago, with it’s strongest effects from 2.8 million to 1.8 million years ago.
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