Now I've played this awesome game recently, called Halo: Combat Evolved ( I'm sure a lot of people have played it already). It's based on intergalactic warfare. A lot of adventures of Master Chief (the main guy) happen to be around on this ring shaped planet-sized thing called the Halo. And the character is actually able to walk around on the inner surface of this. The gravity acts downwards. So is it possible to be able to analytically measure the magnitude of the gravity acting on the inner surface provided we have all the required details? I've managed to find the gravitational field intensity at any point on the axis of the ring. But how do I find it near the surface?