A sound wave’s amplitude relates to the change in pressure caused by the wave measured at a specific location. The sound is perceived as louder if the amplitude increases, and softer if the amplitude decreases.  This is illustrated below.

DOSITS short video on amplitude.

The amplitude of a wave is related to the amount of energy it carries. A high amplitude wave carries a large amount of energy; a low amplitude wave carries a small amount of energy. Amplitude and intensity are related, but not the same. The intensity of a sound wave is defined as the energy transmitted through a unit area, per unit time, in the direction in which the sound wave is traveling; it is a vector quantity having both a magnitude and direction. Energy in a sound wave is comprised of both the pressure component and the particle velocity component (see Science > Advanced Topics > What is intensity?). Sounds with higher intensities are perceived to be louder. Relative sound intensities are often given in units named decibels (dB).

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