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Why is Cracking a Whip So Loud?



The Royal Institution

Cracking a whip causes a small sonic boom as the end travels faster than the speed of sound. Top science bloke Marty Jopson explains the science behind this phenomenon.
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The key to how a whip works is the conservation of energy. Any moving object, including this whip, has kinetic energy. Kinetic energy relies on two things – the mass of the thing moving and the velocity at which it’s moving at. Due to the uncoiling action of the whip, the mass of the whip decreases through the movement and the velocity increases. The handle of the whip moves at roughly 10m/s but the tip of the whip reaches speeds of over 400 m/s which is faster than the speed of sound at 353 m/s.


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42 thoughts on “Why is Cracking a Whip So Loud?
  1. How loud would it be if you create a small vacuum (like in a bulb or something), and then pop it?

    How big of a bubble are we talking here? Would it be the same loud? Or is the collapsing vacuum

    only part of the final sound here?

  2. you forgot to mention the effect of the decreasing diameter of the whip from the handle to the end. The decreasing diameter makes the (cumulative) mass distribution along the whip length from start to end to be non-linear, which, combined with the conservation of energy, further contributes to the speed of the tip. I believe even the varying stiffness of the whip from handle to end also contributes to this. But this is just my $0.02 …

  3. Marty, I am ok with the fact that you are probably at least ten times smarter than me, but that and the facial hair is too much! Why can't I have facial hair like that?! In all seriousness, thank you for the entertainingly given information.

  4. Absolutely fascinating explanation! The world becomes even more amazing with with just a little knowledge of science. (And I'm jealous the lecturer can grow this much hair 🙂

  5. I taught myself how to crack a whip on my own, It was a painful, but very quick learning experience, but I like how this is the Royal Institute and they used MPH, not complaining, just thought it was funny.

  6. So it is a sonic boom. + that other thing you said about cavitation bubble collapse. Now you're all set to go on some adventures Dr Marty Jopson, uncovering mysterious ancient relics.

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