Cracking the Whip

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Science  14 Jun 2002:
Vol. 296, Issue 5575, pp. 1931
DOI: 10.1126/science.296.5575.1931c

Many explanations of how the tip of a bullwhip is accelerated to supersonic speeds include hand-waving (or perhaps arm-waving) arguments and rely on kinematic analysis of the conservation of energy or of linear or angular momentum. In fact, all three quantities are conserved, and a full dynamical treatment is needed to satisfy conservation constraints as well as the known requirements for a good whip, such as a tapered shape. Goriely and McMillen provide a numerical analysis of a loop traveling down a whip and show how this leads to rapid acceleration of the tip. They show that the tip can reach velocities more than 30 times that of the initial velocity, well in excess of the speed of sound. — PDS

Phys. Rev. Lett. 88, 244301 (2002).

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