Why does the earth rotate and what would happen if it stopped?

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Donald asked the Naked Scientists:

I have 2 questions both related. Why does the earth rotate and what would happen if it stopped rotating?

Thank you very much.

What do you think?



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It rotates because it always has, basically. Everywhere you go in space there is turbulence - things spinning around each other and around their own axes. A non-spinning object would be a novelty.

If you add up all the angular momentum (involving spin rate, mass and radius of rotation) in a system, it stays the same. A vast Nebula which is hardly spinning at all will develop, as it collapses in on itself through gravitational attraction, into a Solar System with spinning Star and orbiting stuff where the rotations are much faster - this is because the radius of rotation has got so much less that the spin speed has to increase to conserve angular momentum. (Ice skaters etc. used this too).
btw the conservation of angular momentum means that, if all the planets in our Solar System were hauled in towards the Sun, the Sun would be spinning so fast that it would fly apart again - flinging a lot of orbiting debris out until it was spinning at a manageable rate again. Amazing when you think that there's less than 1% of the Sun's mass orbiting around it and it could make all that difference.
So all stars can be expected to have spinning stuff orbiting round them - just to keep things stable.
« Last Edit: 15/12/2008 15:09:17 by sophiecentaur »



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I cannot believe how smart the people are on this site.I am blown away at some of the answers I have read. But from A goodole country boys point of view;if the world stopped spinning on its axis it would be kind of like the way that mercury spins on its axis constantly keeping the same face of the planet toward the sun at all times and the earth would burn on one side and freeze on the other;causing crazy violent storms due too the convection of the hot air expanding and rushing too the cool side of the earth.But keeping one side of the earth toward the sun would still mean the planet is rotating on its axis.If it completely stopped spinning then our day would be A half year and our night the other half. And the core of the earth would also stop spinning;we would lose our magnetic Field and the earth would burn regardless. But that won't happen because Sophiecentaur is correct. TECHFACTOR:OUT


Offline DoctorBeaver

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There is also the theory that spin was imparted to the Earth by the collision of the planet that caused the moon to form.

The Earth's spin is slowing. Part of its rotational momentum is transferred to the Moon's orbital momentum due to tidal friction. It is this same mechanism that is causing the Moon to recede from the Earth at 4cm per year. That, in turn, means the Moon is taking longer to orbit the Earth (angular velocity blah blah).

What will  happen 1 day, billions of years in the future, is that an Earth day will be equivalent to a lunar month. The Moon will then be geostationary and the tides of the Earth will stop happening (the Moon will stay in the same place above the Earth so its gravity will no longer be affecting different parts of the Earth as it orbits). A day, and a month, will be about 47 days and the Moon will be 33% further away than it currently is.

As a side note, that will mean no more total eclipses of the Sun as the Moon will appear too small to totally obscure the disc of the Sun.
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