# True Cause of Whip's Crack Uncovered

It takes a dexterous hand to coax a whip to crack. Now researchers report that they have discovered the mechanism responsible for the startling sound. It has long been thought that the crack results from the tip of the whip traveling fast enough to break the sound barrier and create a sonic boom. But the new findings suggest otherwise. Apparently, it's the loop in a whip that is the real noisemaker.

Though by no means a master whip cracker, Alain Goriely of the University of Arizona was nonetheless intrigued by the phenomenon and set out to study it at a theoretical level. Together with Tyler McMillen, a graduate student in applied mathematics, he modeled the behavior of the leather strips in a paper to be published in Physical Review Letters. Previous whip work (one of just three papers on the subject in the past century) had resulted in the puzzling observation that the sonic boom occurs when the tip of the whip is traveling at about twice the speed of sound. But if the tip were truly the cause of the crack, why wasn't the sound heard earlier, when the tip first reached the speed of sound? Goriely and McMillen's calculations have revealed the answer. "The crack of a whip comes from a loop traveling along the whip, gaining speed until it reaches the speed of sound and creates a sonic boom," Goriely says. He notes that even though some parts of the whip travel at greater speeds, "it is the loop itself that generates the sonic boom."

Although the whip's tip has lost the distinction of being the source of the menacing crack, it is still a force to be reckoned with: according to Goriely's calculations, "the tip can reach speeds more than 30 times the initial speed [of the whip]."

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1. 1. Whipartist 11:32 PM 9/19/08

As a whipmaker and whip handler of 15 years now, having studied whip physics in great depth, I disagree with this theory as it's stated in this short article.

It starts off on the wrong foot, stating ignorantly.

"It takes a dexterous hand to coax a whip to crack."

Not really. I've taught children to do it in about 3 minutes. A well made whip almost cracks itself with very little effort.

The cracker of a whip, when it cracks, increases in velocity rapidly as it loops around at the end of the whip. It slashing around in a tight loop, and this is when the crack is sounded from the cracker. The loop is irrelevant until it reaches the cracker, at which point it must still remain tight, and only then does it reach enough speed to sound a crack.

They later state, "Although the whip's tip has lost the distinction of being the source of the menacing crack, it is still a force to be reckoned with: according to Goriely's calculations, "the tip can reach speeds more than 30 times the initial speed [of the whip].""

It has not lost this distinction. The cracker is precisely what's making the noise. Take it off and see what happens: No crack. Put a slightly larger one on the whip which isn't properly fitted for it and see what happens: No crack. Put a smaller one on and see what happens: smaller cracking sound. The cracker does generate the crack and anyone handling a well made whip can observe that very simply. Whips can crack even when thrown slowly and the acceleration is still incredible towards the end.

Infact one major aspect of whipmaking that the author is ignorant of is that it's actually the heavier and slower moving whips which cause the louder cracks. Whips that have fine points and produce fast loops within the whip itself and within the end of the whip, cause lower volume cracks than those which conserve energy up until it is finally released into the cracker. They can be so loud that they really hurt one's ears.

The challenge in making fine whips is to make them light enough to be agile, while heavy enough to have a respectable report from the cracker. In facing this challenge over the years, one begins to have an excellent idea of what's happening in a whip's action until one is able to adjust the speed at which a whip accelerates, the power of it's crack and the control the thong has over itself. A perfectly falling whip is a wonderful thing to handle but you'll need to change the crackers often.

My two cents,

Benjamin Scott
www.whipartist.com

2. 2. Tom Nicolazzo 02:50 PM 1/30/10

I bought a brand new six dollar whip -- you can imagine the quality. It works. There is NO loop, at least I can't make one. I bend my elbow to bring the whip straight up, then bring my hand straight down. I get a crack. No loop. The cracker -- a piece of string -- has started to wear out, and the crack has gotten noticably softer.

I have yet to see any physics or actual testing on this theory, not that I would necessarily understand the physics.

The theorists seem to be suggesting that the "tip" -- I assume the author means "cracker" -- *doesn't* make a crack because it's going *faster* than the speed of sound...a conclusion more puzzling than the previous puzzle they were trying to solve.

So, now, who's going to solve the Holmesian question: Why *didn't* the whip tip crack as it broke the sound barrier?

I look foreward to further research.

Tom Nicolazzo

3. 3. bradra 05:33 PM 6/2/10

I just whipped a freshly laundered handkerchief and it popped. Was that a sonic boom?
When one sticks a pin in a balloon is the sound it makes a sonic boom?

4. 4. bradra 05:34 PM 6/2/10

I just “whipped” a freshly laundered handkerchief and it popped. Was that a sonic boom?
When one sticks a pin in a balloon is the sound it makes a sonic boom?

5. 5. Datvette 12:19 AM 12/13/11

I strongly agree with whipartist and Tom. Who does the author think she's kidding? I also make whips but out of braided nylon. I fashion mine after the tried and true shape of those proven by the test of time. I don't even throw a loop when I do my overhead crack. Also I have tried it without the cracker and guess what? No crack! Geez who didn't see that coming? And bradra, when you flicked the handkerchief you got a POOF not a BOOM. Check out the program Time Warp. They use super high speed cameras and they got Adam Winrich, who holds several Guinness Records, to crack the flame off of a candle. The flame provided a target and a focal point for the camera. Guess what they captured on digital media? A shock wave! What we already knew by the sound. I did hear that a very long time ago, before we knew what we know now, that they used to believe that the crack was the tip coming back and hitting itself like clapping your hands. Sarah Graham is this your work or are you just spreading the unfounded ungrounded rumor? I can't figure where your notion got off the ground. And to title it "TRUE cause of whip's crack uncovered" shows you don't even know what you wrote about. Go experiment and find out the difference between a poof and a thunderous crack.

6. 6. Datvette 12:20 AM 12/13/11

I strongly agree with whipartist and Tom. Who does the author think she's kidding? I also make whips but out of braided nylon. I fashion mine after the tried and true shape of those proven by the test of time. I don't even throw a loop when I do my overhead crack. Also I have tried it without the cracker and guess what? No crack! Geez who didn't see that coming? And bradra, when you flicked the handkerchief you got a POOF not a BOOM. Check out the program Time Warp. They use super high speed cameras and they got Adam Winrich, who holds several Guinness Records, to crack the flame off of a candle. The flame provided a target and a focal point for the camera. Guess what they captured on digital media? A shock wave! What we already knew by the sound. I did hear that a very long time ago, before we knew what we know now, that they used to believe that the crack was the tip coming back and hitting itself like clapping your hands. Sarah Graham is this your work or are you just spreading the unfounded ungrounded rumor? I can't figure where your notion got off the ground. And to title it "TRUE cause of whip's crack uncovered" shows you don't even know what you wrote about. Go experiment and find out the difference between a poof and a thunderous crack.

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