Any moving or vibrating object creates changes of pressure in the air around it, changes that move away from it at the SPEED OF SOUND. A SUPERSONIC vehicle, such as a jet plane travelling faster than the speed of sound, has to thrust the air aside as it moves along. This sets up an enormous pressure wave, a shock wave of compressed air that reaches the ear with something of the force of a thunderclap.
No engineering change in the construction of the plane can eliminate this sound. The sonic boom is heard along a strip many miles wide under the entire flight path of the aircraft, and has on occasion caused hundreds of thousand dollars damage.
See: SOUND PHOBIA, SUPERSONIC TRANSPORT. Compare: DOPPLER SHIFT.