THE crack of a whip occurs because the lash’s flailing tip breaks the sound barrier, producing a sonic boom—doesn’t it? Well, not quite. Researchers realised the tip couldn’t be responsible in 1998, when they unexpectedly found it was already moving at twice the speed of sound when the whip cracks. This left them mystified about what makes the cracking sound.
Now Alain Goriely and Tyler McMillen of the University of Arizona have used their equations of motion for a whip to explain what’s going on. It’s the loop travelling along the length of the whip that creates the sonic…
