1. The problem statement, all variables and given/known data Assuming that we know the density of earth as a function of radius, we have to derive the equation for gravity as the function of radius. 2. Relevant equations 3. The attempt at a solution lets us choose density as [tex]\rho[/tex](r). I know that within a hollow sphere there is no gravity. We can assume sum of several hollow spheres with thickness dr, where r is the radius of the shell from center, and then we can integrate it. I know its an easy question we used to do in undergraduate study, but I am missing something and i cant figure out how it was done? Please help!