Overview of a Sonic Boom

A Sonic boom is an impulsive noise similar to thunder. It is caused by an object moving faster than sound, about 750 miles per hour at sea level. An aircraft traveling through the atmosphere continuously produces air-pressure waves similar to the water waves caused by a ship’s bow. When the aircraft exceeds the speed of sound, these pressure waves combine and form shock waves, which travel forward from the generation or “release” point.
As an aircraft flies at supersonic speeds it is continually generating shock waves, dropping sonic boom along its flight path, similar to someone dropping objects from a moving vehicle. From the perspective of the aircraft, the boom appears to be swept backwards as it travels away from the aircraft. If the plane makes a sharp turn or pulls up, the boom will hit the ground in front of the aircraft.
The sound heard on the ground as a “sonic boom” is the sudden onset and release of pressure after the buildup by the shock wave or “peak overpressure.” The change in pressure caused by sonic boom is only a few pounds per square foot, about the same pressure change we experience on an elevator as it descends two or three floors, in a much shorter time. It is the magnitude of this peak overpressure that describes a sonic boom.
There are two types of booms: N-waves and U-waves. The N-wave is generated from steady flight conditions, and its pressure wave is shaped like the letter “N.” N-waves have a front shock to a positive peak overpressure, which is followed by a linear decrease in the pressure until the rear shock returns to ambient pressure. The U-wave, or focused boom, is generated from maneuvering flights, and its pressure wave is shaped like the letter “U.” U-waves have positive shocks at the front and rear of the boom in which the peak overpressures are increased compared to the N-wave.

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