Sound is a vibration travelling through matter — Physical education, 11–13 years
Sound begins with something vibrating and reaches us through a material such as air, water or metal. Its pitch and loudness come from different features of that vibration.
How sound travels
A vibrating object nudges nearby particles, which nudge the next particles, making a moving pattern. Your eardrum responds when that pattern reaches it. Sound needs matter to pass through, so it cannot travel across the empty space between planets.
Why vibrations explain sound
People needed to explain why a plucked string, a drum and a voice can all make sound. Looking closely showed that each source vibrates, and those vibrations disturb the surrounding material. This idea also explains why astronauts cannot talk directly in space without radios or another connection.
A tuning fork
A tuning fork marked 256 Hz vibrates 256 times each second after you strike it. Those vibrations make nearby air particles move in a repeating pattern, and the pattern reaches your ear. A fork marked 512 Hz vibrates twice as often, so it produces a higher-pitched note, not simply a louder one.
Pitch is not loudness
People often call a high note a loud note because both can feel intense. The mistake is reasonable: faster vibrations can sound sharp and noticeable. But pitch depends mainly on frequency, the number of vibrations per second, while loudness depends mainly on how large the vibrations are.
Sound in technology
Microphones use a thin part that vibrates when sound reaches it, then turn that motion into an electrical signal. Speakers do the reverse: an electrical signal makes a part vibrate and create sound. Ultrasound scanners use vibrations above human hearing to make images inside the body.
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