longitudinal wave, wave consisting of a periodic disturbance or vibration that takes place in the same direction as the advance of the wave. ... Sound moving through air also compresses and rarefies the gas in the direction of travel of the sound wave as they vibrate back and forth.
FORMULA
[tex]y(x,t) = y0 \: cos \: (w(t - \frac{x}{c} ))[/tex]
y = displacement of the point on the traveling sound wave
x = distance the point has traveled from the wave's source
y_0 = amplitude of the oscillations
\omega = angular frequency of the wave
t = time elapsed
c = speed of the wave
