As an added problem to the ''hole through the center of the earth'' theory...
If you jumped into said hole, when you passed the middle you would begin to slow down and eventually go back the way you came.
I think you''d end up in a sort of simple harmonic motion swinging back and forth if friction was ignored.
If there IS friction, you''d get stuck in the middle of the earth at some point with no way to get home.

quote:Original post by shadow12345
I''ve never heard that before, why is that so?

It''s kinda like Gauss''s Law for Electricity, only for gravity in this case. If you have a closed Gaussian surface, according to Gauss''s Law the electric flux though this surface is only proportional to the charge inside the surface. Now, replace charge with matter, and replace electric flux with gravitational flux (rough translation ). Assume that r is less than the radius of the object. The enclosed matter increases at a quadratic rate, but the distance falloff is inverse squared. They cancel out. But since surface area increases at a linear rate, the net increase in gravitational force is linear.

Once r is greater than the radius of the object, it behaves like a regular point mass, and the usual rules apply (inverse square falloff force).