A sonic boom is a loud, explosion-like sound created when an object travels through the air faster than the speed of sound. This occurs as concentrated pressure waves, known as shockwaves, generated by the object, reach an observer.
What is the Speed of Sound?
Sound travels through a medium, such as air, as pressure waves. These waves are vibrations that cause the molecules of the medium to compress and decompress, transferring energy. The speed of these waves is known as the speed of sound, or Mach 1.
The speed of sound is not constant; it changes based on the medium’s properties. Air temperature significantly influences this speed, with sound traveling faster in warmer air and slower in colder air. Altitude also plays a role, as temperature and air density decrease with increasing height, affecting how quickly sound propagates.
The Creation of a Shockwave
When an object, such as an aircraft, approaches the speed of sound, the pressure waves it generates begin to compress. These waves cannot outrun the object once it reaches or exceeds Mach 1. Instead, they pile up, forming a sudden, intense change in air pressure known as a shockwave.
As the object travels at supersonic speeds, it continuously generates these shockwaves, which trail behind it in a conical shape. This is often referred to as a Mach cone or shock cone. The leading edge of this cone is where the main pressure build-up occurs, extending outwards and backwards from the object’s path. A sonic boom is not a single event when an object “breaks” the sound barrier, but a continuous effect produced as long as supersonic flight is maintained.
Experiencing the Boom
The shockwaves generated by a supersonic object propagate outwards from the Mach cone, eventually reaching the ground. When this concentrated pressure wave passes over an observer, the sudden change in air pressure is perceived as a loud “boom.” Depending on the object’s design and flight profile, an observer might hear two distinct booms: one originating from the nose of the object and another from its tail.
Several factors influence how a sonic boom is experienced on the ground, including the object’s altitude and its aerodynamic shape. Higher altitudes generally result in a less intense boom because the shockwaves have more distance to dissipate before reaching the ground. Atmospheric conditions, such as temperature, humidity, and wind patterns, can also refract or reflect the shockwaves, altering their path and perceived intensity by ground observers.