[Tim_Lou]

imagine 2 bodies in space. one is the sun, the other is the planet. they are perfectly rigid and spherical. these 2 bodies are separated quite far apart. Imagine the non-uniform gravitational field the planet experiences. due to its non-uniform nature, gravitation force do not act exactly at the planet's center of mass (the position should be a little bit closer to the sun than the center of mass).

Consider this: when the earth spin at a non-zero inclination angle, the gravitation pull would result in a net torque on the planet, which results in precession.

i have worked out a approximation of this torque (10 page paper..). what i did was basicaly directly integrating over the whole sphere (the planet) while using some reasonable approximations in between. however, no one has ever validate it nor do i know if it is mathmetically correctly or has been discovered before...

any comments or inputs are appreciated. if you are interested, i can post my project.

[Erasmus00]

These fores due to the non-unifrom nature of the gravitational field are known as tidal forces. Googling should give you lots of interesting information.
-Will

[Tim_Lou]

hmm, very interesting, never thought of internal strain caused by these forces.

i can imagine these force causing current to flow in the magma resulting in a magnetic field. I hope I'm not too far off, am I?