Spin at the Cushion

Learn the movement.

At an object ball, the contact normal follows the line of centers and both balls can move. At a cushion, the rubber pushes back and surface friction couples travel with rotation. Its nose contacts above the ball’s equator. A simple angle-in/angle-out mirror is a useful ideal reference, not a full model of a spinning pool ball.

Running English tends to carry the ball farther along the contacted cushion and lengthen the rebound. Reverse checks that travel and can shorten or change it substantially. For the lab’s prepared far-cushion approach, right is running and left is reverse. Mirroring the approach swaps that relationship.

Topspin and backspin affect the cushion collision and the curve that follows as the ball meets cloth again. Speed, side-to-speed ratio, and cushion condition can change the result. A bank sends the object ball to a cushion; a kick sends the cue ball there. An object ball’s acquired spin is not automatically the same as the English you put on the cue ball.

For a real table, start with no intentional side, repeat the line at one pace, then compare small amounts of side and high/low. Record where the ball arrives instead of inventing a universal extra diamond for every tip of English.

What changes the result?

Distance, pace, contact point, spin at collision, balls, cloth, and execution can all matter. Keep the basic setup consistent before comparing one change. An exact-looking line is not evidence of an exact physical prediction.