The whip's pop is a result of the tip of the whip (the "popper") moving
beyond the speed of sound and creating a vacuum in space. The air
rushing back into the vacuum makes the pop sound. A whip generates its
speed through the "conservation of energy". The body of the whip is
built to be a continually shrinking diameter from the thick handle down
to the tip of the popper which is only a few strands of fiber. A little
energy imparted at the handle accelerates along the diminishing diameter
until the popper is moving over 700 miles/hour. You scientists can post
the exact speed of sound (someone's .sig says that "the speed of time is
one second per second" :-)