# Earth's Rotation

1. Dec 28, 2009

### skepticsm

I have a question about the centripetal acceleration required for earth's rotation about its axis. There obviously must be a force causing this acceleration, but I can't seem to figure what the source of this force is. Anyone happen to know the answer?

2. Dec 28, 2009

### Staff: Mentor

For any piece of the earth not on the axis of rotation there will be a net centripetal force. Gravity and contact forces (from surrounding material) provide the radial force, the net of which is towards the axis of rotation.

3. Dec 28, 2009

### sweet springs

Hi,
Regarding the earth as simple solid body, no outer force is required for spinning of the earth by the conservation law of angular momentum.
Regarding the earth as complex of parts, part of gravity to the center of earth works as centripetal force to keep them not dispersed.
Regards.

4. Feb 13, 2010

### LouieHussey

Skepticsm, centripetal acceleration is in the radial direction, but the earth’s rotational motion is in the tangential direction. As such, centripetal acceleration does not cause the earth’s rotation--I am taking the earth's radius to be a constant here. Did you mean to ask: what torque acts upon the earth to cause its rotation?

Last edited: Feb 13, 2010
5. Feb 14, 2010

Rain.