system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is special about the speed of sound? What causes a sonic boom?
gpt
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.