Why does a whip make a cracking sound when someone whips it? --- Thomas, Englishtown, N.J.
Marshall Brain Answers:
That cracking sound you are hearing is a sonic boom. The tip of a long whip goes supersonic and makes the sound. The following video demonstrates how to make a whip and crack it:
Here is the tip in slow motion:
This article puts a finer point on it:
"A whip is specially crafted to accelerate a loop in its body to high speeds. The tapering of a whip makes a loop traveling along it speed up by a factor of ten. The lightweight free end allows an extra factor of two to three in speed. For realistic whips, the tip can reach speeds more than 30 times the initial speed," he said.
See also: Time Warp: Whip Through Soda Can