Spin and Object-Ball Contact

Learn the movement.

The line connecting the ball centers at impact is the frictionless object-ball direction. Surface friction adds a tangential impulse. Cut-induced throw can occur with no initial sidespin; spin-induced throw depends on the sidespin present during contact. Squirt changes the cue ball’s initial line, while throw changes the struck object ball’s direction.

On a near-full hit, right sidespin can throw the object ball left of the line of centers and impart a little opposite sidespin. Most of the cue ball’s side need not disappear. Cut contact can also generate spin on both balls even when the cue ball started without intentional side. That transferred spin can matter if the object ball later banks.

At the gearing amount of outside English, relative sideways rubbing can be reduced, reducing throw. Extra outside is not automatically more accurate: too much can reverse the throw direction. Ball cleanliness, pace, cut, and vertical spin all matter; real throw is not a fixed angle per tip of side.

For the cue ball, stun, draw, and follow determine its departure and subsequent curve. A cut-stun reference starts near the tangent; residual forward or backward rotation then affects the later route. The lab models horizontal contact friction and cloth reaction, while real vertical contact effects and skid are more involved.

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.