What is a Sonic Boom?
A sonic boom is a booming noise heard from land when an aircraft flies beyond the speed of sound. Once a plane breaks the speed of sound, it is called supersonic.
This phenomenon is similar to how a boat creates a wake in water. When objects travel through the air at supersonic speeds, molecules are pushed to the side with great force (creating a shock wave). The size and mass of the aircraft determine how much air is displaced.
Speed of Sound
Let’s pull some numbers on how fast sound actually travels. Sound travels at various speeds depending on the altitude, temperature, and substance it is going through. At sea level 68 degrees Fahrenheit, sound travels around 761 MPH. At 20,000 feet, sound travels at about 660 MPH.
Double Booms
Aircrafts generate two cones of the sonic boom - one at the nose and one at the tail. The size of the sonic boom is dependent on the size, weight, and shape of the aircraft. One might perceive a sonic boom as a single sound, however, it could actually be a double impact sonic boom hitting the ground. This is due to the two cones of the sonic boom generating.
Altitude Effect
The distance that the shock waves travel before reaching the ground is determined by altitude, and altitude will also significantly influence the intensity of the shock wave. As the shock wave spreads wider (moving outward and downward), the strength of it is reduced. The higher the altitude of the aircraft, the more distance the shock wave has to travel; this lowers the intensity of the sonic boom impact.
There is an apparent sonic boom “carpet” beneath the aircraft that, as a general rule of thumb, is about one mile for each 1000 feet in altitude. A supersonic speed airplane at 40,000 feet could produce a cone about 40 miles wide. Typically, parts of the sonic boom carpet are weaker than others.
Courtesy of François Coulouvrat
Measurement
How does one measure a sonic boom? Sonic booms are measured in pounds per square foot (psf) of “overpressure.” It is the amount of increase over the normal atmospheric pressure that surrounds us (2,116 psf/14.7 psi).
One pound overpressure would not cause damage to structures on ground (though between one to two pounds would be noticeable).
At two to five psf overpressure, some minor damage could occur.
Bullwhip - Sonic Boom
Whenever you hear the sound of a bullwhip crack, it is also a sonic boom. A loop travels along the speeding whip until it reaches the speed of sound (some parts travel even faster than the speed of sound!). Some often attribute the crack of the whip to the tip, but it is the loop itself that generates the sonic boom. However, the tip is still a noise maker speeding more than 30 times the initial speed of the whip.
More information:
NASA Armstrong Fact Sheet: Sonic Booms
https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-016-DFRC.html/
What is a Sonic Boom?
<https://wonderopolis.org/wonder/what-is-a-sonic-boom/