I have some questions regarding collision angles. I am trying to code physics for a game and I do not want to use any third party library, actually I want to code each and every thing by myself. I know how to detect collisions between two spheres but I can't figure out, how to find the angle of collision/repulsion between the two spherical objects. I've tried reversing the direction of the objects, but no luck. It would be very nice if you link me to an interesting .pdf file teaching physics programming.