Any noise you hear is coming from something that is moving in the air.
When something moves and makes noise, we say it vibrates.
Most things that make noise move so fast that you can't see them.
But there are things you can see how they move when they vibrate.
Take a long thin object, a ruler or spatula, and place it on the end of a table. Push it down with your finger. Let it go. You'll see it move up and down. It's vibrating. Can you hear the buzz it produces.
When the ruler vibrates, pushes the air around her
and it vibrates too. The vibrations of the air are called sound waves. These vibrations or sound waves travel outwards, like the waves in a lake; when they reach your ear, make an internal part of it vibrate. That's precisely when you hear the sound.
If the ruler protrudes far enough from the table, will rock up and down, slowly. When it oscillates slowly, produces a low sound. If the ruler just sticks out a little, will swing rapidly. So, the noise is sharp.
test it. Listen to the various sounds the ruler makes when, holding it fixed by one end, you make it vibrate.
