The amount of work done to generate the energy that sets the particles
in motion is reflected in the degree of displacement which is measured
as the amplitude of a sound.
The frequency f of a wave is
measured as the number of complete
back-and-forth vibrations of a particle
of the medium per unit of time.
1 Hertz = 1 vibration/second
f = 1/Time
Depending on the medium, sound
travels at some speed
c which defines
l: l = c/f