Now I am going to stir the pot. English on a cue ball takes effect on the cue ball after hitting the rack, not just after hitting a rail! The reason is simple. The mass of the rack is far greater than the mass of the cue ball, so it has more effect on the primary forward force of the cue ball. This can allow the secondary force on the cue ball, the spin, to have much more effect after forward motion is checked by impact with the rack.
Hu
How does the "secondary force" of sidespin change the path of the CB at any time, before or after hitting anything? In order for spin to have any effect on the CB's path there must be some rotation around a horizontal axis. How does sidespin, which is rotation around a vertical axis, do this?
pj
chgo