Particle displacement or
displacement amplitude is a
measurement of
distance of the movement of a particle from its equilibrium position in a medium as it transmits a
sound wave. The
SI unit of particle displacement is the metre (m). In most cases this is a
longitudinal wave of pressure (such as
sound), but it can also be a
transverse wave, such as the
vibration of a taut string. In the case of a
sound wave travelling through
air, the
particle displacement is evident in the
oscillations of air
molecules with, and against, the direction in which the sound wave is travelling.