Sonic boom
The sharp pressure impulse heard when the Mach cone of a supersonic source sweeps past an observer.
Definition
When a source moves faster than the speed of sound in its medium, the pressure wavefronts it emits cannot run ahead of it. They pile up on a cone trailing behind the source, called the Mach cone. The air along the surface of this cone is at higher pressure than the surroundings.
When the cone sweeps past an observer on the ground, they experience a sudden jump in pressure followed by a sudden drop — the characteristic double-crack of a sonic boom. The boom is not emitted only at the moment a vehicle crosses the sound barrier; it is emitted continuously for as long as the vehicle stays supersonic.
History
The geometry was worked out and photographed by Ernst Mach in 1887. Supersonic flight in aircraft was first achieved by Chuck Yeager in the Bell X-1 on 14 October 1947.