What does the amplitude of a sound wave affect?  

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The amplitude of a sound wave is associated with the loudness of the sound. The larger the amplitude, the louder the sound. Likewise, the smaller the amplitude, the softer the sound.

Sound waves are longitudinal waves. In a longitudinal wave, the displacement of the wave is the same as or opposite to the direction that the wave travels. Thus, longitudinal waves appear to move “in and out” as opposed to the “up and down” of a transverse wave.  Longitudinal wave compressions are areas where the wave is “squished” together, whereas rarefactions are areas where the wave appears to be “stretched”. The amplitude of a longitudinal wave is the maximum increases of pressure from a point of equilibrium that is caused when the wave passes a given point.

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