Long ago, a loud sound, also known as a sonic boom, shook the city of Bengaluru. An Indian Air Force (IAF) test flight, which involved a supersonic profile, was the source of this sonic boom. This incident has brought about a renewed interest in sonic booms and how they are produced.
Understanding Sonic Booms
Sonic booms are shockwaves that are produced by objects or planes flying at or above the speed of sound, which is around 1225 kilometres per hour at sea level. As an airplane travels through the air, it generates sound waves. However, if the airplane flies at a slower speed than the speed of sound, the sound waves actually get ahead of the airplane.
Conversely, if the plane breaks the speed of sound barrier and travels faster than the speed of sound, it produces a sonic boom when it passes by. This sonic boom is essentially a combination of the plane’s sound waves all being propagated at once. The reaction of the air to supersonic objects is similar to the way fluid reacts. As these objects move through the air, molecules are displaced forcefully, leading to the formation of a shockwave. Larger and heavier aircraft will displace more air.
The Cause of Sonic Booms
The shockwave forms a cone of compressed or built up air molecules, moving outward and rearward in every direction, extending all the way to the ground. As this pressurized cone spreads across the landscape along the flight path, it constantly creates a sonic boom throughout the entire base of the cone.
The rapid release of pressure following the buildup by the shockwave is what we hear as a sonic boom. The change in air pressure associated with a sonic boom is only a few pounds per square foot, roughly equivalent to the pressure change experienced traveling two or three floors down in an elevator. But it is the sudden change in pressure which makes the sonic boom audible.
Factors Influencing Sonic Booms
Several factors can influence sonic booms. These include the weight, size, and shape of the aircraft or vehicle, its altitude, attitude and flight path, as well as the weather or atmospheric conditions at the time.
The direction of travel and strength of shockwaves are subject to the speed and direction of the wind, plus atmospheric conditions like air temperature and pressure. Understanding these factors and how they interact with each other is key to understanding the nature of sonic booms.
