Particle displacement or particle amplitude ξ is a distance measurement in m (metre) of the movement of a particle(real or imagined) in a medium as it transmits a wave. In most cases this is a longitudinal wave of pressure as with sound, but it can also be a transverse wave as with the vibration of a taut string. When applied to a sound wave through a medium of air, particle displacement would be the physical movement back and forth of a molecule of air in the direction the sound wave is travelling as it passes.

It can be represented in terms of other measurements:

Symbol	Units	Meaning
ξ	meters	Particle displacement
v	m/s	particle velocity
ω = 2 · π · f	radians/s	angular frequency
f	hertz	frequency
p	pascals	sound pressure
Z	N·s/m³	acoustic impedance
J	W/m²	sound intensity
E	W·s/m³	sound energy density
Pac	watts	sound power or acoustic power
A	m²	Area
a	m/s&sup2	Acceleration

See also

• Particle velocity
• Sound pressure
• Wave