Physics & Geometry

When the cue ball strikes an object ball, the object ball travels along the line connecting the two ball centers at contact — the impact line. The cue ball travels along the tangent line, perpendicular to the impact line, until spin takes over.

This is the single most important geometric fact in pool. It means the cue ball's post-contact direction is determined by the cut angle, not by where you were aiming.

For a rolling cue ball (natural roll, no draw or follow applied), a half-ball hit sends the cue ball almost exactly 30° off the impact line. Half-ball means the cue ball's edge lines up with the center of the object ball at contact.

This gives you a fast mental model: on a normal-speed cut, the cue ball leaves at ~30° from where the object ball went. Use it to plan the very next shot.

Where you strike the cue ball changes what it does after contact:

• Center — pure stun; cue ball stops or takes the tangent line.
• Above center (follow) — cue ball continues forward after contact.
• Below center (draw) — cue ball reverses after contact.
• Left/right (English) — no effect on the object ball's path; changes cue ball's angle off the rails.

Deflection (also called squirt) is the small sideways push English gives the cue ball as it leaves the tip. Every cue has its own deflection profile; you learn yours through practice.