about sound

there are many sounds in our life， some of them  are soft, and some of them are loud.

in our life, sounds are like: music, the sound of birds, Or the sound of a car.

that sounds off the bird, and the music was very soft and many people love them, this sounds off the car sometimes are very loud, and nobody likes them.

there are many different sound, but what is the same of all the sounds?

that is, all the sounds are energy.  but why?That's because sound is produced by vibration. Let's take a tuning fork. if we use something to knock on it, we'll here the tuning fork  can make sounds, We can also see vibrations.

so we could know that sounds are produced by vibration.