We just learned about Positive and Negative sides of batteries.
When you make a sound, like plucking on a guitar string, it makes a vibration that pushes through the air.
(from: wikipedia - seven strings guitar)
Those invisible vibrations in the air are called sound waves and if you could see them you'd see they look a lot like the waves you see in the water.
(from: wikipedia - sound waves)
The waves travel through the air until they hit your ear, then you hear the sounds!
(from: wikipedia - ear)