Waves> Sounds are wave <#5679,2><!vibrations> that travel through air. But why are they called “sound waves,” anyway? The waves we know well are water waves, from tiny ripples in a pond to crashing waves at the beach. To understand sound waves better, toss a pebble in a pool of water, and look carefully at what happens.
The splash from the pebble pushes up and down on the water, causing a small vibration. A ripple forms - a small ring of water wrinkled into hills (called crests) and valleys (troughs). As the ripple moves outward away from the center, the ring of moving wrinkles gets bigger and bigger across as the hills and valleys of the wrinkles themselves gets smaller and smaller. If the ring passes a tiny float on a fishing line, then as the hills and valleys slide by, the float bobs quickly up and down.
The ripples are water waves, upward and downward vibrations of the water, in a pattern that travels across the pond. Their energy causes the float to vibrate up and down in turn. If you measure how quickly the ripples travel across the pond, you’ll know the speed of the wave.
With sound, you can’t see the air moving like you can with water. And, sound waves aren’t “up and down,” since air is all around in three dimensions. Instead, the waves in the air are “squeezes” of the air. The crests are places where the air has been squeezed together by the wave, and the troughs next to them are the places where the air has unsqueezed itself. This pattern repeats itself as invisible wrinkles in the air, that move outward in all directions, just as the water ripples moved out across the water’s surface.
When these ripples in the air - sound waves - reach an object, they push and pull on it, like the water does on the small float. And so eardrums, and microphones, are vibrated by the moving wave. And that’s how our ears pick up the energy of the sound, and we “hear” it.
