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A whip's tip travels over 1,400 feet per second when the whip is cracked -- much faster than the speed of sound, which is about 1,230 feet per second. Thus, the crack of a whip is actually a small sonic boom. The "crack" is the sound of air rushing back into the small vacuum created by the whip's cracker. How do whips manage to achieve this velocity? As NewScientist.com explains, good whips gradually taper from handle to tip. A smart flick of the wrist sends a wave down the length of the whip. As roughly the same amount of energy acts on a progressively tapered (and smaller) mass, its velocity increases. Why? Because of the first law of thermodynamics. The
conservation of energy principle states that the total energy of an isolated system remains constant, regardless of changes within the system. The whip is an isolated system. Since the "whip-snap energy" in this case is a function of mass and velocity: As the mass of the tapered whip decreases, the velocity of the snap increases. Believe it or not, the same theory applies to snapped towels.
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