   Colliding Spheres
  I have a very simple question...Given two spheres, a and b, how can I determine the rebound effect of their collision given their position, velocity, radius, and mass.  I already know how to calculate at what positions they will be at the time of impact, I just don't know where to go from there.  It should be simple, but I'm having a brain-block.  Neither sphere possesses any elasticity.Thanks in advance for help.   