Bullwhip
The cracking sound a bullwhip makes when properly wielded is, in fact, a small sonic boom. The end of the whip, known as the "cracker", moves faster than the speed of sound, thus creating a sonic boom. The whip is probably the first human invention to break the sound barrier.
A bullwhip tapers down from the handle section to the cracker. The cracker has much less mass than the handle section. When the whip is sharply swung, the energy is transferred down the length of the tapering whip. In accordance with the formula (if the work for whipping remains constant) for kinetic energy, the velocity of the whip increases with the decrease in mass, which is how the whip reaches the speed of sound and causes a sonic boom.
Read more about this topic: Sonic Boom