Sound

Sound is a type of energy, a physical phenomenon that moves through a medium such as air/gas, a liquid, or a solid. It is a sound (acoustic) wave created by a source that travels outward and can stimulate a person's sense of hearing.

A sound starts as a vibration from a source such as machinery, an engine, or a human voicebox. It disturbs the surrounding medium (such as air), causing it to vibrate and travel as a wave. The vibration can be received by the human ear and interpreted as a sound by the brain.

In air, sound is usually described as a variation in pressure (either above or below atmospheric pressure).

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