I need a formula that yields the speed and angle after a 2D collision that uses the coefficient of restitution (e). Preferably this would also be relativistic. I have searched EVERYWHERE for this and could not find it. To "prove" that I have indeed tried I have read the collision sections of Classical Mechanics by R. Douglas Gregory, Mechanics, Volume 4 By Ted Graham, Aidan Burrows, Brian Gaulter, Physics for Scientists and Engineers, Volume 2 By Lawrence S. Lerner, Impact Mechanics By W. J. Stronge, Engineering Mechanics: Dynamics By Russell C. Hibbeler, and MANY more....I have also searched extensively online to no avail. Please find/derive this formula for me! Thanks! The most useful thing I have found so far is: http://books.google.ca/books?id=oVL...icient of restitution collision angle&f=false This gives a non-relativistic speed using COR but I need the angle too but not for the scenario I describe (a 2D collision between two spheres) - perhaps someone could also explain how to get that from the formula there. Does the COR only effect v and not the angle? Shouldn't a speed formula be independent of the incident angles (and that be factored in with the calculation of the exiting angle)? Thank you for any and all help!