—Bettina H. Chavanne
We hear a sonic boom when there is a sudden change in pressure—a shock wave—in the air around us. The shock wave is caused by the continuous buildup and violent release of air pressure along the surfaces of an airplane traveling at supersonic speeds. During subsonic flight, pressure waves continuously move away from the aircraft in all directions, like the waves that spread out from a boat’s bow as it cruises through water. At supersonic speeds, however, the pressure waves emanating from the leading edges and fuselage of the aircraft merge into one large pressure gradient, then release suddenly as they escape from the nose (the bow shock) and tail (tail shock) of the aircraft, resulting in a loud double-boom sound.
The pressure increase of a sonic boom, as experienced on the ground, is only about one to two pounds per square foot, a change someone would feel going down a couple of floors in an elevator. But because the change is so sudden, it not only registers on human eardrums as a loud noise, it also has the power to break glass and cause other structural damage.