Context: Recently, sonic boom (a loud sound) was heard in Bengaluru which emanated from an Indian Air Force (IAF) test flight involving a supersonic profile.
Background

• Sound travels in the form of waves which are emitted outwards from its source. In air, the speed of these waves depends on a number of factors, such as the temperature of the air and altitude.
• From a stationary source, such as a television set, sound waves travel outwards in concentric spheres of growing radii.
• When the source of sound is moving – e.g, a truck– the successive waves in front of the truck get closer together, and the ones behind it spread out.
• This is also the cause of the Doppler Effect– in which bunched waves at the front appear at a higher frequency to a stationary observer, and spread out waves that are behind are observed at a lower frequency.
• As long as the source of the sound keeps moving slower than the speed of sound itself, this source– say a truck or a plane – remains nested within the sound waves that are travelling in all directions.

About sonic boom

• It is said to occur when an object travels through the air faster than the speed of sound and creates shock waves.
• This can lead to a huge emission in energy, usually in the form of sound, which can be similar to an explosion of thunderclap.
• According to NASA, it is a thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound, or “supersonic.”
• Air reacts like fluid to supersonic objects. As those objects travel through the air, molecules are pushed aside with great force and this forms a shock wave, much like a boat creates a wake in water. The bigger and heavier the aircraft, the more air it displaces.

General Factors Associated with Sonic Booms

• There are several factors that can influence sonic booms — weight, size, and shape of the aircraft or vehicle, plus its altitude, attitude, and flight path, and weather or atmospheric conditions.
• A larger and heavier aircraft must displace more air and create more lift to sustain flight, compared with small, light aircraft. Therefore, they will create sonic booms stronger and louder than those of smaller, lighter aircraft. The larger and heavier the aircraft, the stronger the shock waves will be.

Aircraft and Sound

• The sonic boom is a continuous sound which is emitted by the aircraft all the while it is travelling at a supersonic speed.
• If the aircraft is flying at a low altitude, the sonic boom may also lead to tremors similar to earthquakes and shattering of glass.

Examples of sonic boom

• A sonic boom can be produced while cracking a whip through air. This happens because the whip travels at a supersonic speed and breaks the sound barrier.
• The loud noise produced when a bullet is fired from a gun is also a sonic boom, as the bullet travels at supersonic speed.
• A sonic boom is most commonly heard when an aircraft is travelling at a low altitude, which leads to a very loud boom and tremors in the ground.