Squeeze and stretch
What Does a Sound Wave Look Like?
Sound is not a wiggly line in the air. It is bands of crowded and thin air moving outward.
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Step 1 of 5
The drawn wiggle is a graph.
That familiar wave shape is a plot of air pressure over time. It is not the shape the air makes — the air never wiggles up and down.
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Step 2 of 5
The air moves back and forth along the direction of travel.
Each patch of air shuffles forward and back a fraction of a millimetre, passing the squeeze along the line. That is called a longitudinal wave.
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Step 3 of 5
Squeezed bands and thin bands alternate.
Where air is crowded, pressure is high. Where it is stretched thin, pressure is low. Those bands march outward at 343 metres per second.
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Step 4 of 5
Band spacing sets the pitch.
Close-together bands mean many squeezes reach your ear each second — a high note. Widely spaced bands mean fewer, so a low note.
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Step 5 of 5
Band strength sets the volume.
How crowded the crowded bands get decides loudness. Big pressure swings mean a loud sound; gentle ones mean a quiet one.
A bass note has a wavelength of several metres. That is why you feel bass through walls — long waves bend around obstacles easily.
The short version
A sound wave is bands of crowded and thin air travelling outward; the drawn wiggle is only a graph of the pressure.
Try it yourself
Stretch a slinky on the floor and push one end sharply. A squeeze travels down it — that is a sound wave you can watch.
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