Whips and Dinosaur Tails | Science News

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Math Trek

Whips and Dinosaur Tails

9:02am, September 16, 2002

The loud crack of a deftly flicked bullwhip can certainly command attention. That distinctive noise is a small sonic boom, generated when the whip's thin, highly flexible tip exceeds the speed of sound.

Swinging a leather bullwhip's thick, rigid handle in an arc gives the whip angular momentum. Sharply reversing the motion's direction sends a wave down the whip. As the wave travels toward the tip along a tapering path, it moves more and more rapidly–a consequence of the conservation of angular momentum. In the end, the narrow tip's supersonic motion through the air produces a shock wave.

The same conservation principle is at work in the flicking of a locker-room towel or, at subsonic velocities, during a golf swing, karate chop, or javelin throw.

Noise-making whips can be made from various materials, including paper, fiber, and leather. Though the designs may differ in many respects, such whips typically have a tapering cross sect

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