Let's say there are two rigid bodies in space, each has an initial translational velocity as well as an initial angular velocity. Eventually, these two bodies collide. The collision causes the translational and angular velocities of both bodies to change, resulting in 4 unknowns (each unknown being a vector). All of the initial conditions are known, as well as all information about the collision point. I need four equations to solve the problem. So far, I have three: conservation of linear momentum of the system, conservation of angular momentum of the system, and the coefficient of restitution equation at the collision point. I can't figure out the last equation to give me my last unknown. Any ideas?