So i'm completely lost...here's the problem. There's a small ball inside an empty sphere. How can I prove this sphere doesn't attract the small ball gravitationally, independently of the position of the ball inside the sphere?? Also, how can I use the result from above to find the gravity force acting on some body of mass (m) inside a planet of radius (R) and mass (M) if this body is at distance r<R from the center of the planet. (The density of the planet is uniform). Thanks ahead of time.