A whip cracks because a rapidly moving loop travels down its tapered length, transferring energy toward a section with progressively less mass.

As the loop approaches the narrow end, its speed rises sharply. Part of the whip can exceed the local speed of sound, creating a shock wave similar to a small sonic boom. The sound comes from compressed air, not from the tip striking anything.

High-speed imaging shows that the fastest point may lie within the moving loop rather than at the absolute tip. Its exact motion depends on the whip’s taper, stiffness, and the way it is swung.

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