1. The problem statement, all variables and given/known data planet with mass m and uniform density and radius r, show by integration that the force this body generates on say a satelite is equivalent to a point mass m at the center of the planet 2. Relevant equations i know that gravitational pull is inversley to r*r 3. The attempt at a solution I tried breaking the sphere down into horizontal discs, then each disc into rings. in each ring the force on the satelite above it is mMsin(*)/d*d where * is the angle between the satelite and mass round the ring. I tried integrating all the rings into a disc, then all the discs into the whole planet but couldnt do it?? There must be an easier way to show a planet can be represented by a point mass?