Whip Physics

How does a whip crack?

To understand this, let's first discuss the sound barrier and sonic booms. Sound travels through the air in vibrations. These disruptions form a wave. The speed of sound is on average about 767 miles per hour at 68℉. When an object approaches that speed, the sound waves compress. This is known as the doppler effect. When the object accelerates past the speed of sound, it breaks through the compressed ”wall” of sound waves, resulting in a sudden release of energy, and in turn a sonic boom. When a whip is thrown properly, a loop forms and begins to travel down the whip. Because the whip tapers in size and weight, this loop becomes an accelerated wave decreasing in size and increasing in speed as it moves down the whip because a larger heavier part of the loop is pulling a smaller lighter part as it rolls. At the top of the loop, before it collapses, the end of the cracker is pulled through the sound barrier; it has achieved mach 1 and will release a small sonic boom. This does not happen at full extension of the whip but rather just before. A cracker is not needed for a whip to break the sound barrier but it makes it easier and more effective.