where ______ is the coefficient of tangential restitution. As B decreases from the fully elastic case, __ = 1, the rebound velocity of the point of contact decreases until ___=0 for which no rebound occurs and there is instantaneous rolling of the ball. For ___=-1, the ball has a perfectly smooth surface and there is no change in the spin or the velocity. For the intermediate case of ______, there still slipping between the ball and the surface, but energy is assumed to be lost primarily to friction. The use of a coefficient of tangential restitution is a simplified approach to modeling the sliding contact of the ball, which, in a more realistic model, would include Coulomb friction. In a more realistic model of the collision, the energy losses would depend on both the normal and tangential velocities of the ball. Even with this change in Eq. 3), the forces on the ball continue to act through the point of contact and the torque about this point remains zero. Thus, angular momentum is conserved while the energy is not. With conservation of an momentum and Eq. (6), the x component of the velocity and the spin of the ball after the collision become