Say i Have 1. A perfectly spherical and perfectly rigid Ball 2. A perfectly flat and perfectly rigid wall Say i throw the ball at my FLAT wall also giving the ball a linear velocity The only contact with the wall and the ball is a point... a POINT !! So, I can as well forget about the rest of the wall except the POINT ( Forget the wall but keep in mind of the point that the ball collides with. I did that since the existence of the rest of the wall has no effect on the after-collision motion of the ball. Here, I'm also assuming the wall and the ball are perfectly rigid so they meet at a single point only ) The point would have resisted the motion of the ball in the opposite direction to the velocity of the ball( makes sense, as the motion is an example of 1D collision ) And the ball also move back on the same path but in opposite direction like stuff in 1D motion do. The rigid body of the ball is made of a set of points at a certain fixed distance from each other The point of contact of the ball and the point of contact of the wall are in 1D motion The point of contact of the ball which has initial velocity v now has a velocity that is in opposite direction, V ( at the instant of collision) If the other points continue to be in v, the distance between the points change... I see only two thing the body could do to stay rigid; for all the set of points to instantly have the velocity, V after collision or for the body to rotate ( or does it want to stay rigid at all? )Anyways..... If it does move in V all at once, the ball will retrace it's original path ! so.... no matter how the wall was aligned as long as the ball makes a point sized contact,... the force may or may not have been perpendicular and the ball WILL HAVE traveled the same path in reverse That's my intuition .. but do correct me if i'm wrong .... or is the whole problem is wrong to the base? ( don't say that my assumption of a perfectly rigid/perfectly flat/ perfectly spherical object is impossible... it's fun when such stuff are involved in calculations) What's your predictions of what will happen after collision?