Assume both billiard balls have same mass and same radius. So situation 1: ball 1 is moving forward without slipping on a surface and collides elastically with ball 2 which is stationary on that same surface. I read that immediately after the impact, ball 1 stops and keeps spinning with its original spin while ball 2 is imparted with the same CM velocity that ball 1 had. Does ball 1 not impart any spin to ball 2 because there is no kinetic friction between them? Now situation 2. Two identical billiard balls of radius R and mass M rolling with velocities ±⃗v collide elastically, head-on. Assume that after the collision they have both reversed motion and are still rolling. Below is initial picture before collision. Now situation 2 should be similar to situation 1. So why is it that they reverse motion in all aspect? They should only swap linear velocities. But their spin was swapped as well. Ball one is now counter clockwise whereas it wasn't before. But there is no vertical contact force from the collision since there is no friction from the contact of the balls surfaces. That is ball one cannot alter the spin of ball 2 and vice versa. So why does the spin gets traded in this case verse case one where it didn't?