Equations · equation
Thirty-Degree Rule
Billiards
- Equation
- a rolling cue ball leaves a ¼- to ¾-ball hit at about 30° from its original line
- Field
- Billiards
- Symbols
- the deflection of the cue ball's final rolling path from its incoming line, for a naturally rolling cue ball and a medium cut
Significance
Not a law but a consequence: the ninety-degree rule sends the cue ball down the tangent line, then its topspin — which the collision did not touch — bends it forward as it takes up roll again. Over the middle range of cuts that bend lands the ball near 30° from where it was going, which is why a peace sign held at the object ball predicts where the cue ball ends up. Faster shots and thinner or fuller hits break it; stun (no roll) keeps the ninety.
Referenced by
equation
skill
Open on the Equations shelf — the interactive card, the filters, and everything alongside it.