In a previous paper [1] two of the present authors considered in detail the mechanics of a superball bouncing back and forth on a rough horizontal plane.Reversals in direction in the horizontal motion of the ball result from the application of a tangential law of restitution at the point of impact of the ball and the plane.This concept was first in troduced by Garwin [2] who used a tangential coefficient of restitution o fone,which is not physically realistic. Garwin’s model was modified by Cross [3] who employeda tangential coefficient of restitution a satisfying 0oao1, with the
horizontal velocity of the point of impact of the ball being reversed and reduced in magnitude by a factor of a in theimpact.Further details of the physics of this model are given in [1],together with references to other theoretical and experimental work.