I'm writing a program that simulates circular "particles" in 2d space. I'm at the collision handling part. I've already corrected their positions when an overlap occurs. So, my question is, how do I determine the angle of each particle's velocity after the collision? I have the position and velocity vectors of both particles, so I can easily calculate the angle each particle is moving in before the collision and the angle from one particle toward another. http://nubcraft.org/stuff/img/collide.png [Broken] Thanks for any help.