Snapple Cap Facts have taught us all that the first man-made device to break the sound barrier is the tip of a whip when properly cracked. But why does that happen? It’s actually a classic example of the physics law relating to the conservation of angular momentum. The cause of the phenomenon is found in the loop that’s formed in the whip as it is cracked. A whip becomes increasingly thin going from the handle to the tip. According to the law of the conservation of angular momentum, if the rotational inertia of an object decreases then its speed must increase. In terms of cracking a whip, the mass of the whip decreases as the loop moves closer to the tip, thus the velocity of the loop increases. It continues to gain speed until it reaches the tip of the whip, at which point it is supersonic, causing the familiar cracking sound.

But not all whips are made to be cracked.

Unlike lunge or carriage whips, which feature a long, rope-like lash, the so-called straight whip, for instance—a long, fairly rigid device with only a short snap on its end, is meant to cue the horse or other livestock by lightly touching its flank or shoulder, not by making a cracking sound.