What causes sound? Is it a type of energy that is emitted when objects collide? (actually, that’s an interesting theory, but incorrect). When you hear of sound waves and their having a certain speed, that is a little misleading, and I will tell (I can’t really ‘tell’ anything, as I am typing, and you use light to understand this, not sound as in speech, so, I guess I will, um, ‘type’) you how sound works.
Say I have a recorder, and I blow through the mouthpiece. This sends air down a tunnel (B) to an edge (C). This separates the air blown into it, and the air inside the tube is thrown all wild and the molecules start shaking around, while still being being pushed down the tube. If all the holes on the recorder are covered, the molecules stop moving around so much. If only a few holes are covered, then the molecules keep shaking/vibrating. When the air is out of the recorder it continues vibrating, and so shakes the molecules around it, which in turn shakes the molecules around that with the same velocity and shaking as the originals. And so the vibration spreads, all the way to our eardrums, which pick up the vibrations and send the signals to the brain. The faster the vibration, the higher the pitch, and too fast of vibration can break our eardrums, making us deaf (thankfully, it takes a lot of vibration to do that).
Have you ever looked at speakers while the sound is on and on loud? The air around the emitters is distorted, as if vibrating, which it is. Also, when objects collide, the air around it shakes with the force, and that vibration force spreads to our ears, which once again pick it up.