My problem may be complicated or simple (I guess complicated). I'm having problem solving a general (or theorical) situation of colision between two objects having both angular and linear velocity. The result I want to obtain is the force that needs to be applied for a time (dt) so that the colision is fully elastic with resulting new angular and linear velocity for each object. What is known before colision for both objects is : all moments inertia, mass, velocity, angular velocity, forces at CM, torque at CM, position. Maybe some have guessed it , this is for a physic engine applied to a 3d engine, that's why it's a general problem. It could also be helpful to have the colision deal with external forces (not equal to zero). thank in advance for any response.