Sonic boom

A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion. The crack of a supersonic bullet passing overhead or the crack of a bullwhip are examples of a sonic boom in miniature.

When an aircraft passes through the air it creates a series of pressure waves in front of it and behind it, similar to the bow and stern waves created by a boat. These waves travel at the speed of sound, and as the speed of the object increases, the waves are forced together, or compressed, because they cannot get out of the way of each other. Eventually they merge into a single shock wave, which travels at the speed of sound, a critical speed known as Mach 1, and is approximately 1,225 km/h (761 mph) at sea level and 20 °C (68 °F).

In smooth flight, the shock wave starts at the nose of the aircraft and ends at the tail. Because the different radial directions around the aircraft's direction of travel are equivalent (given the "smooth flight" condition), the shock wave forms a Mach cone, similar to a vapour cone, with the aircraft at its tip. The half-angle between direction of flight and the shock wave ${\displaystyle \alpha }$ is given by:

where ${\displaystyle {\frac {v_{\text{sound}}}{v_{\text{object}}}}}$ is the inverse (${\displaystyle {\frac {1}{Ma}}}$) of the plane's Mach number (${\displaystyle Ma={\frac {v_{\text{object}}}{v_{\text{sound}}}}}$). Thus the faster the plane travels, the finer and more pointed the cone is.

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