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FAQ: What Makes a Whip Crack?

July 21, 2009

whipcracksonicboom

In years past, most people assumed that the crack of the whip was the end of the whip hitting against itself.  Around 1905, scientists began to suspect however, that the crack was in fact a sonic boom.  In 1927 technology reached the point where scientists were able to use high-speed photography to actually see the sonic boom created by the tip of the whip, and at that point we knew for sure that Whip Crack = Sonic Boom.  So interestingly, humans had been creating objects that break the sound barrier for literally centuries before Chuck Yeager broke the sound barrier in his rocket-powered aircraft.

In 2002, Scientific American published an article about another scientist, Alain Goriely.  This physicist had been puzzled by earlier findings which suggested that the tip of the whip may have been traveling faster than the speed of sound at the time of the “crack,” and after much research, concluded that it must instead be the loop near the tip of the whip breaking the sound barrier that caused the crack, not the tip of the whip breaking the sound barrier.  Click here to read the full article from Scientific American.

These new findings are debated by some whipcrackers and whipmakers, and the belief that it is the tip of the whip passing the sound barrier which creates the “crack” is still the most common explanation you’ll find.  I’ll let you decide for yourself which specific theory you want to believe, but at the very least we do know for sure that whether it is the loop at the tip of the whip or the tip of the whip itself that creates the sonic boom, the “crack” is most certainly caused by the end of the whip breaking the sound barrier.

The reason the tip of the whip accelerates to such high speeds is a bit simpler to explain, thankfully.  A whip begins with a wider diameter, and tapers to a much much smaller diameter.  The whipcracker imparts energy to the beginning of the whip with his or her arm, and as the energy travels down the tapering whip, the energy is amplified exponentially and the speed of the loop traveling down the whip therefore also accelerates exponentially.  Until, at last, some part of the end of the whip breaks the sound barrier and creates the sonic boom.

One of the most common misconceptions on this subject is that the popper or cracker of the whip is necessary to create the crack.  I am no scientist, but I can tell you from direct experience that the popper is NOT needed for a whip to produce a crack.  Most whipcrackers have at some point accidentally lost the popper from the end of their whip during a whipcracking session, and not noticed right away.  The whip does still crack without the popper, though it might not crack quite as crisp or directed of a crack as it was with the popper on.

Poppers serve two main purposes. First is to continue the taper of the whip and provide an ending to the whip which helps to better direct the sound of the crack. Second is to serve as the most easily and inexpensively replacable part of the whip and help preserve the fall. If a whip is cracked even just a handful of times without a popper, the end of the fall will begin to fray just like poppers do. And even though falls are fairly easy to replace as well, poppers are much more economical and simpler to replace.  (If you’re a bit lost and don’t really know what falls or poppers are, be sure to check out Whip Terminology: Part 1 – then this whole last paragraph will make a lot more sense).

In parting, I will leave you with a really fun video clip from the Discovery Channel’s show TimeWarp, featuring Adam “Crack” Winrich, professional whip artist, performer and entertainer.  There is a little bit of discussion in this clip on the fact that a whip cracking is actually a sonic boom, and they do a little super-slo-mo camera work so you can see the tip of the whip as it is cracking.

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