Sound comes from vibrations — Physical education, 7–10 years
Sound starts when something moves back and forth. You can feel this movement in a guitar string, a speaker or your own throat.
A moving shake makes sound
When an object vibrates, it makes nearby air vibrate too. Those moving waves reach your ears, and your brain hears them as sound. Touch your throat while speaking: you can feel your vocal cords shaking.
Why look for the vibration?
People noticed that drums, strings and voices make sound in different ways, but all involve movement. The vibration idea solves a puzzle: how can a silent object suddenly make a noise? It also explains why stopping a drum skin stops its sound.
A ruler on a desk
Place 10 centimetres of a plastic ruler over the edge of a desk and hold the rest down. Pluck the free end: it bends, springs back and vibrates, making a note. Press it so it cannot move: the vibration stops, so the sound stops too.
The air is not the source
It is reasonable to think the air makes sound because sound travels through air to your ears. But air usually carries the vibration rather than starting it. A struck drum, a vibrating string or your vocal cords begins the movement; the air passes it on.
Music and communication
Guitars, piano strings, drum skins and loudspeakers all use vibrations to make sound. Your voice does too, so speech depends on controlled vibrations in your throat and mouth. Hearing aids and microphones detect sound vibrations and turn them into signals.
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