The two forms of energy in a wave are kinetic and
potential. Denoting them at a particular time
and position
by
and
, respectively, we can write them in
terms of velocity
and wave impedance
as follows:
More specifically,
and
may be called the acoustic kinetic
energy density and the acoustic potential energy density, respectively.
At each point in a plane wave, we have
(pressure equals wave-impedance times velocity), and so
where
denotes the acoustic
intensity (pressure times velocity) at time
and position
.
Thus, half of the acoustic intensity
in a plane wave is kinetic,
and the other half is potential:B.30
Note that acoustic intensity