Eli5: Why does a sonic boom occur when you break the sound barrier?
In: Physics
You know when a fire truck or ambulance is coming towards you, the siren is higher pitched, but when it moves away the sound becomes lower? This is called the Doppler effect – the source of the sound is moving. As such, the sound waves become “bunched up” in front of the vehicle – the distance between the waves is smaller, creating a smaller wavelength, resulting in a higher sound. The reverse is true behind the source of the sound – a wider gap is created between the waves, meaning a greater wavelength, meaning a low sound.
A supersonic jet breaking the sound barrier means that it is going faster than the speed of sound – that is, the source of the sound is so fast, it catches up with the sound waves ahead of it. The resulting buildup of energy releases in the form of the sonic boom – the air particles in front of the jet collide with each other.
I hope that this was useful, and that my terminology is accurate and scientific – this is about all I can remember from all of physics at secondary school!
Also, the crack of a whip is actually a miniature sonic boom. As the whip is flicked, the wave of motion accelerates along its length until it breaks the sound barrier at the tip.
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