Video: Loudspeaker (sound wave)

Sound is a mechanical wave that propagates in compressible media.

In air, symbolized here by little balls, the passage of a sound wave will set the air molecules in motion.

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We are dealing with a pressure wave.

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By freezing the image we can distinguish  between zones of compression (with a high density of molecules) and zones of  rarefaction (with a low density of molecules).

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If we observe the red molecule, we’ll see that it is indeed the wave of pressure that is propagated and not the air.

Each molecule simply vibrates over a few micrometers around its equilibrium position.

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To emit a sound, all that is needed is to set the air in motion.

But to hear this sound, its frequency must be within the human hearing range,  that is between 20 and 20,000 Hz.