compression is larger than the impulse during the expansion,
with the result that the ball rebounds at a speed less than the
incident speed. The plasticene ball did not bounce and remained
permanently deformed after the collision. All of the
hysteresis curves have a finite area, indicating that all collisions
were inelastic. The golf and superballs have an approximately
linear compression phase, with F}y, and a nonlinear
expansion phase.
The y displacement wave forms are more closely sinusoidal
than the force wave forms, at least during the compression
phase. In all cases it was found that the ball rebounds
in a compressed state since y remains finite at the end
of the impact. This was confirmed for the tennis and superballs
by aligning the beam L2 , as shown in Fig. 1, so that it
grazed the top of the ball when the ball was at rest on the