~3! A large diameter disk was chosen to avoid saturation
of the force wave form that would occur if the contact area of
the ball exceeded the area of the disk. Even so, measurements
for a tennis ball were restricted to velocities less than
8ms21 since the contact diameter of the ball exceeded 50
mm at ball speeds greater than 8ms21
. In the case of a highspeed
tennis ball, or a large diameter ball such as a basketball,
a piezo larger in diameter than 50 mm would be