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Asked by emmagrace to Dalya, Derek, Sarah, Tim, Tom on 19 Jun 2011.
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Dalya Soond answered on 17 Jun 2011:
At the centre of the earth is a huge ball of liquid iron. It is always spinning and causes the earth to spin with it, like a toy top.
This is different from orbiting. Orbiting is when you move around another object, not around yourself. The Earth orbits around the sun because of the gravitational pulls from the sun.
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Tom Crick answered on 18 Jun 2011:
One of the reasons why the Earth rotates is down to the law of conservation of angular momentum: the Earth has never stopped rotating since the early periods of the solar nebula because there is nothing in the vacuum of space to stop it! So when it started rotating in the early development of the solar system, nothing has ever exerted a force to stop it (luckily).
The only thing that may stop the Earth’s rotation is the gravitational forces of the Sun after it begins to expand into its red giant phase (in a few billion years time).
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Derek McKay-Bukowski answered on 18 Jun 2011:
As Tom says, the Earth rotates because it has always done so… and there is nothing to slow it down. A spinning ball on a table will slow down because of friction with the table and (a little) friction with the air. The Earth has nothing like that, so it just keeps on spinning.
Tom’s right in that when the Sun expands into a red-giant star, it will slow down the Earth’s rotation. But it is NOT the gravitational forces directly. Instead, the Sun’s atmosphere will expand out to engulf the Earth and the Friction will slow the Earth down. When that happens, it can no longer sustain its orbit and it will begin to lose altitude (which makes things worse!). Eventually it will plummet into the heart of the Sun and be lost forever.
It is just as well the Earth is in a nice orbit for now. As Dalya says, the gravitational pull of the Sun helps with this. It stops the Earth flying off into deep space. However, it also has to have some speed, otherwise it would just fall like a stone into the Sun.
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Tim Millar answered on 19 Jun 2011:
Derek, are we winding up space time in our loical gravity well? Will that not have some effect over time?
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