This is an issue I have not seen addressed often. For a practical application consider a rack of pool balls and the collision on the break. I have tried to model this by approximating 3 ball collisions which looks ok, but I think my method is incorrect. Solving for energy in these situations I think may be impossible. I really haven't looked into it that much. I know the basic 2 ball collision doesn't work in these situations. What I was really looking for was a fast way to distribute energy through a connected net of touching objects ( which I can build by detecting collisions over time intervals). I need to propagate energy through the net. Each object has different velocity. It could just be an approximation and does not have to solve for energy for my purposes. I also need an algorithm that does not get stuck in infinite loops and resolves so that the next instant in time does not result in a new collision within the network of objects. One that takes into account for different elasticity of objects would be impressive. Anyone ???