The article and paper presented by him is reproduced below. For pictorial results, click here.
Abstract:
A ball, struck with a sufficient impulse above centre, will leave the table after hitting the cushion. This is due to the angular momentum of the ball and the force due to the friction of the cushion. The analysis of this phenomenon was performed using a video camera (filming at 60 frames per second) and a strobe light (flashing at 180 Hz). On the table this experiment was performed on the cushions were of very poor quality and nearly half the energy of the ball was lost in the collision.
Introduction:
The elasticity of the cushions of a billiards table is very important in a quality table. A good way to measure this is to actually have the ball leave the table after the collision with the cushion and measure the energy of the ball before and after the collision. By having the ball leave the table one source of error is removed: friction. The cushions are set up as to keep the balls on the table by having the contact point above the centre of the ball. To overcome this compensation, a high angular velocity, and hence velocity, is needed to have the ball lift off of the table. The ball leaves the table because the friction of the ball on the cushion due to the spin of the ball is translated into a diagonal force tangent to the ball at the contact point. In fact almost all of the rotational energy is turned into vertical kinetic energy. The energy of the ball should be conserved if the cushion's rubber has no internal resistance. The ratio of the energy of the ball after the cushion and before should be 1. In the calculations below it is assumed that: a) before the cushion the ball does not slip and therefore the angular velocity is the velocity of the ball divided by the radius of the ball; b) the angular velocity of the ball after the cushion is zero; c) the ball does not slip in colliding with the cushion.
Experimental Procedure:
