Sonic boom

The sonic boom is the sound produced as a result of aircraft traveling at or above Mach 1 (the speed of sound) or indeed, when any object breaks the sound barrier. As an object moves through the air it creates pressure waves that move radially outward at the speed of sound. When the object moves at or above the speed of sound the waves that would normally propagate ahead of the object merge into a larger pressure wave.

It used to be thought that the cracking noise of a whip was due to leather striking leather but, after using high speed photography to study the motion of the whip, it was discovered that the crack is actually the tip of the whip breaking the sound barrier.