Particle velocity

Particle velocity is the velocity v of a particle (real or imagined) in a medium as it transmits a wave. In many 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 velocity would be the physical speed of an air molecule as it moves back and forth in the direction the sound wave is travelling as it passes. Particle velocity should not be confused with the speed of the wave as it passes through the medium, i.e. in the case of a sound wave, particle velocity is not the same as the speed of sound.
In applications involving sound, Particle velocity is usually measured using a logarithmic decibel scale called particle velocity level.

Equations in terms of other measurements

The velocity v can be related to the particle displacement <math>\xi</math> and acceleration for single frequency plane wave of frequency f using

<math>

v = \xi\cdot \omega = \xi(2 \cdot \pi \cdot f) = \frac{p}{Z} = \frac{a}{\omega} = \sqrt{\frac{E}{\rho}} = \sqrt{\frac{P_{ac}}{Z \cdot A}} </math> It is further related to the instantaneous acoustic intensity vector I (not the time-averaged averaged acoustic intensity) according to

<math>

v = \frac{I}{p} </math>

See also

• Sound particle
• Particle displacement
• Particle acceleration
• Pressure gradient

External links

• Ohm's law as acoustic equivalent - calculations
• Relationships of acoustic quantities associated with a plane progressive acoustic sound wave - pdf
• The particle velocity can be directly measured with a Microflown
• Acoustic particle-image velocimetry - development and applications