Spin Physics Quiz:

Improve your cue ball control with these insightful quiz questions. These questions come from facts that escaped my intuition as I was figuring out the 3-D spin physics to model spin accurately in Masse Pool. If you get half of them right, consider me impressed. These affects can all be observed in Masse Pool.

Q: Why can you not bank a ball 6 times lengthwise?

A: It's not just because of imperfect elasticity in the rails, it's because the rolling spin picked up by the balls slows the ball after each rail collision.

Q: Let's say you hit the cue ball dead center with a level cue to strike an object ball dead center 3 feet away. Consider how far forward the cue ball rolls after the collision if you hit the ball at a normal speed. If instead you struck the ball extremely hard, would the cue ball roll further forward, forward by the same amount, less forward, or would neither roll forward.

A: The cue would roll less forward if struck extremely hard. In either case the cue ball stops at the time of the collision. It is the rolling spin of the cue ball when the collision occurs that causes the cue ball to follow forward. When the cue ball is struck at a normal speed the cue ball has time to begin to roll. When struck extremely hard, the cue ball does not have time to pick up much rolling spin. So it does not roll forward very far.

Q: In a frictionless rail collision, the angle of incidence equals the angle of reflection (high school physics). On a real table, will a rolling ball with no english (side spin) reflect closer to parallel to the rail, or closer to perpendicular.

A: It will reflect closer to perpendicular. This is due to the friction of the ball against the rail (which also applies side spin). However, the rolling spin of the ball actually causes the angle to go closer to parallel after its effect is realized. So either answer was partially correct.

Q: Is it possible to hit the cue ball slowly the distance of the table into the far rail at a right angle and have it reflect at a non-right angle?

A: Yes. Since the ball is hit slowely it will be rolling when it hits the far rail. It may be surprising that a rolling ball can have english (side spin). A rolling ball whose axis of rotation is parallel to the bed of the table has no english. However, a rolling ball's axis may be anywhere in the plain perpendicular to it's velocity. NONE of the english that is applied by striking the cue ball with the cue is lost by the rolling spin picked up by the cue ball.