same direction.An important difference between sound waves and the waves we’ve been studying
on stretched strings is that the molecules of the medium transmitting a sound wave
move parallel to the direction of wave propagation, rather than perpendicular to it.
For this reason, sound waves are said to be longitudinal. Despite this difference,
all of the basic characteristics of a wave—amplitude, wavelength, period,
frequency—apply to sound waves as they did for waves on a string. Furthermore,
the all-important equation λf = v also holds true. However, in order to show an
oscillating wave on a graph for a longitudinal wave, since the medium motion does
not oscillate up and down, we instead graph pressure versus time.
The speed of a sound wave depends on the medium through which it travels.