Subject: RE: Billiards and Physics Date: Mon, 5 Mar 2001 09:38:53 -0500 From: John Botsford <JBOTSFORD@equitable.ca> To: 'Fu-Kwun Hwang' <hwang@phy03.phy.ntnu.edu.tw> John Botsford wrote: > > The law of reflection can only be used in billiards to > approximate the angle of reflection for a billiard ball. Since > the rails of a pool table are rubber, the ball will sink into > the cushion to varying degrees depending on the velocity of the > ball. This amount that a ball sinks into the cushion changes > the angle of reflection. For instance, the faster a ball is > moving when it hits the rail, the sharper the angle of > reflection will be. The law of reflection is a close > approximation only if the ball is moving relatively slowly. The > other thing that affects the angle of reflection is the spin on > a ball. In the case of the cue ball, spin is often purposely > mparted to the ball by striking it off center in order to change > where the cue ball will end up. As for object balls, spin is > imparted to them by contact with other objects (balls and > rails). This spin also changes the angle of reflection. >