What sound is

Listen closely and you hear many different sounds around you. The energy that gives us the sensation called hearing is sound.

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Figure 4.21 — two traditional musical instruments being played: a harmonium and a pair of tabla drums.

Every sound starts with a vibration

Many animals make sounds by vibrating a part of the body, and every other sound is produced the same way — by something vibrating.

A tree frog

This South American frog inflates a balloon-like sac under its throat. Air pushed out of the sac vibrates two thin membranes in its mouth, and the call carries about ten times as far as other frogs'.

A bee

A flying bee's buzz comes from its wings beating rapidly back and forth.

A grasshopper

Grasshoppers and crickets rub the ridges on one leg against another leg to make it vibrate.

Your voice

Our voice comes from the vocal cords in the voice box vibrating.

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Figure 4.22 — a tree frog of the kind that calls using an inflatable throat sac.

We hear these sounds because the sound travels through the air to our ears as a wave.