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Shock waves and sonic boom
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Source faster than sound generates a cone of compression.
sinθ = v/v_sA source moving faster than the wave speed outruns its waves, forming a cone with half angle sinθ = v/v_s. The sudden pressure jump is heard as a boom.
Concorde at Mach 2: θ = 30°.
The boom is continuous along the track, not a one-time event.
In more detail
When a source moves faster than the speed of sound, the waves overlap to form a cone-shaped shock wave. Passing through it produces a loud bang called a sonic boom.
Real-world uses
- Supersonic aircraft produce sonic booms that are carefully managed.
- Bullets moving faster than sound create shock waves that can be heard as cracks.
- The sonic boom from a supersonic jet is a shock wave, the cone of compressed air that forms when the source outruns its sound.
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Frequently asked questions
Why is it called a boom?
The shock wave arrives as a sudden pressure change, which we hear as a bang.
Do aircraft always produce booms?
Only when they fly faster than the speed of sound at ground level.
Is a sonic boom heard once?
It is heard as a boom when the cone passes over the listener, though the aircraft may cross many points during its flight.
Related topics in Waves & Sound
Doppler with moving source · Doppler with moving observer · Doppler in light · Mach number · Energy transport in waves · Wave packets and group velocity