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Compression and expansion creates pressure waves that are the sound​ waves we hear and feel.

Sound Waves can Interfere

Like all waves, sound waves can constructively, or destructively, interfere with other sound waves.

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Noise cancelling headphones work by producing sound waves that destructively interfere with noise.​

Resonance happens when reflected waves constructively interfere with incoming waves.

Resonance depends on Speed of Wave, and length of cavity or string that bounds the wave.

In two dimensions, resonance depends on the shape of the surface (Drum), and speed of wave.

We can use sound in 3D to levitate objects!