Torque for rotation

Question

The force for revolution of earth is provided by the gravitational force of attraction between earth and the sun. What provides the force(torque) for the rotation of earth?

Relared: http://physics.stackexchange.com/q/23104/2451 and links therein. — Qmechanic, Jan 19 '14 at 18:21

score 1 · Answer 1 · answered Jan 19 '14 at 16:03

Your first statement is wrong, so this question makes no sense. There is no acceleration, so no torque.

This is a lot like a top keeps spinning after you start it. It will eventually slow down due to friction, but the earth it rotating in the vacuum of space, so has no friction to anything else.

Actually tidal forces cause things to slosh around on the earth, which causes some internal friction, which is slowly converting the rotational energy of the earth into slightly warmer oceans and the like. However, the fraction of energy lost each rotation is so tiny compared to the whole that the earth is slowing down very very slowly in human terms. It takes advanced instruments to measure it.

Excuse me sir I didn't quite got you could you please explain a bit further? — Dws_kool, Jan 21 '14 at 01:51

score 0 · Answer 2 · answered Jan 19 '14 at 15:56

There is no torque that causes the rotation of earth today. Many years ago, before the earth existed as a planet, matter in space started to clump together due to gravity. As this clumping occurred, more matter would crash into the larger and larger clump at some angle. These crashes create a rotation in the clump. This rotation remains to this day.

Torque for rotation

2 Answers2