UNDERSTANDING WAVE MOTION

Still confused? Here's a simple analogy

Imagine you have 50 people, all standing in a line, each one with their hands on the shoulders of the person in front. Because we don't want them to move too far, we glue everyone's shoes to the floor. And because we don't want them to actually fall over, we put big springs connecting everyone's chest to the back of the person in front.

Got the picture? What we've done is to set up a model of how air particles behave - push one and they'll all move, but not at the same time.

Now we need a source of sound - in other words, something that provide a source of mechanical vibration in our model. So - bring in a large wrestler, put their hands on the shoulders of the person at the end of the line, and get them to push - HARD - and then pull back just as hard. You will get a wave of compression (people all squashed together) followed by a wave of rarefaction (people leaning away from each other) running all the way down the line.

This is analogous to a sound wave moving through air. The people themselves don't move far at all - they only move backwards and forwards, the same as air particles. That's what waves are all about. Energy is transferred from one end of the medium to the other, but the particles through which this energy passes hardly move.

In short, a sound wave is just a series of moving pressure zones travelling long distances through a medium which itself doesn't move much at all.