I have used Newton's law of restitution without problem in collisions between point objects but there seems to be a problem in its application in eccentric impacts. I have always thought it is applied to points on rigid extended bodies that come in contact during the collision for eccentric collisions.[applied here implying their velocities are considered in the equation-- (-velocity of separation/velocity of approach) = e ] But I recently came across suggestions on this forum that velocities of centres of mass of the extended objects is to be considered instead. Am I getting it wrong? Regrets if I am asking a stupid question.... For reference here is the link to the thread: https://www.physicsforums.com/showthread.php?t=435457"