I am writing a 2D simulation that involves multiple circles colliding with inclined planes. I want to collision response to be as true-to-life as possible but have hit a bit of a snag. Depending on the velocity of the circles, when colliding with the inclined planes, they may either bounce off the plane, or they may not bounce and just begin rolling down the plane. Is there a single mathematical model which would accomidate bothe of these instances. I am trying to make the calculations as straight forward as possible, with out any conditionals.