Equations · equation
Cushion Rebound
Billiards · 1835
- Equation
- v_n,out = e_c v_n,in; the tangential component and side spin lose to cushion friction
- Field
- Billiards
- Year
- 1835
Symbols
v_n the speed component into the cushion, before and after · e_c the cushion's speed restitution — about 0.87, from retaining ¾ of the energy · the component along the rail is reduced by friction, and side spin is partly converted to it
Significance
The rail gives back most of the speed that hit it square and slows what ran along it, so the ball leaves at a shorter angle than it arrived — more so when it arrives fast. Side spin adds or subtracts to that along-rail component: running english lengthens the angle and keeps the ball moving, reverse shortens it and kills speed. Cushions are rubber, not physics constants; every table plays a little differently, and players test them before a match.
Referenced by
equation
skill
Open on the Equations shelf — the interactive card, the filters, and everything alongside it.