# What is special about the speed of sound? What causes a sonic boom?

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What is special about the speed of sound? What causes a sonic boom?

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The speed of sound is actually the (average) speed each individual air particle is moving at. So, if you start going faster than that speed, you run into the air, and the air can’t get out of the way fast enough, so it just bunches up in a big cone behind you. That is your sonic boom.

Theres nothing special about the speed of sound. When an aircraft reaches speeds around the speed of sound, air pressure builds up, which is then released when it reaches speed of sound.

1) What we call sound is basically particles (of air, of water, of your desk, whatever) slamming into each other and transferring energy, like billiard balls hitting each other and moving about a table. The “speed of sound” isn’t constant, it depends on A. the material the sound is moving through and B. the conditions of that material (temperature being a big one). So sound has a speed in air around us, which is different than the speed of sound under water which is different than the speed of sound in a metal bar. So the speed of sound in air isn’t “special”, it’s just the speed of sound in air.

2) Imagine dropping a rock into water, it creates small ripples that go outwards. That’s kind of like making a sound, ripples of energy traveling outwards. Now image the boat starts moving, as the boat cuts through the water it creates a series of small and medium waves around it, right? There is a special place behind and to the sides of the boat where those small and medium waves kind of *combine* and stack up on each other to create a BIG wave, the boat’s wake. A sonic boom is like a sound wake. It’s a place behind and to the sides of an object moving at the speed of sound where sound waves are being stacked up on top of each other to create a sound-wake behind the object.

If you have the chance, watch Will Smith’s documentary on National Geographic “welcome to earth”. The first episode is about sounds in nature such as volcano etc. They basically explain through some exemples that sounds also move air and you can actually feel the sound in your body. Really fascinating series of 6 episodes

The Speed of sound is a measure of how fast a pressure wave can move through the air. Sound is just a pressure wave. When you go faster than that pressure wave can move away from the aircraft, it builds up at the leading edges of the aircraft increasing the pressure. The higher the pressure, the louder the noise generally. The Sonic boom is that big pressure wave created by the aircraft reaching your ears. Also, the density of the air affects the speed of sound. The higher you go above sea level the lower the air density and the lower speed of sound.

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Fun fact if you want to get real nerdy, some jet engines like in the SR-71, take advantage of this pressure wave by directing it into the engines to make them more efficient. Called Ramjet engines.