[sci.space] Faster than sound

Hans.Moravec@ROVER.RI.CMU.EDU (02/14/89)

As Arthur Clarke has pointed out in several books, the crack
of a whip is a sonic boom caused by the tip exceeding the
speed of sound. As the momentum in the heavy part of the
whip near the handle moves in a wave towards the lighter
tip, the velocity increases, until it exceeds that of sound,
and *CRACK*.  The taper of the whip serves to incrementally
match the high impedance of one end with the low impedance
at the other.