Where Does Sound Come From?
Somebody or something causes every sound we hear. Sounds are the result of disturbances in the air. Sound is produced by waves in the air. The buzz of the bumble-bee is caused by the quick movement of his wings in the air. The wings themselves do not make the sound, but their motion causes waves or vibrations in the air which produce the sound of buzzing. Every motion made by anybody or anything produces waves in the air just like the waves you see in the water—a big movement makes a big wave and a tiny movement a tiny wave. When you clap your hands you make a disturbance in the air which causes a sound—the harder you clap the louder the sound. You can hear this sound and anybody else near can hear it. If there were no air about us, however, we would hear no sound, even if we could live in such a condition of things, for it is the air waves produced striking against the drum of our ears that enable us to discern sounds. When we talk we make air waves also and thus produce sound. If you were deaf, and talked, you could not hear any sound, because even when there are air waves they must still strike against a sounding board in order to be recognized as sound—and the drum of our ear is our sounding board for hearing sounds.
When the air waves produced are regular we call the sound musical, and when they are irregular we call it noise. Some people can make musical sounds when they sing, while others cannot.
If you take a piece of thin wire and stretch it tightly, fastening it at both ends, and then pull it with your finger and let go, you will hear a musical sound, because the vibrations produced will be regular and will continue for some time. If you shorten the distance on the wire where it is fastened at both ends and pull it as before, the sound produced will be in a higher key. If you take a guitar and snap the big G string you will produce the bass note of G. If the other G string (the smaller one) is in tune (if you watch the smaller one closely while you strike the larger one) you will notice the smaller one vibrate also. Sound waves of the same tone, although in different octaves, produce the same sounds, although in different keys.
This is the principle on which the piano is made to produce music. Inside the piano are wires of different lengths and the keys of the piano are arranged to operate certain little hammers, each of which strikes a certain wire. Every time you strike a piano key you cause one of the little hammers to hit its wire—the wire then makes vibrations which cause air waves. The air waves strike against the sounding board which is located behind the wires, and being thrown back into the air, strike against the drum of our ears, and we can hear the note.