Question

why is sound wave called a longitudinal wave

Answer 1

HEY DEAR....!!!

Longitudinal waves are waves which propagate parallel to the direction of propagation of the wave. Sound travels in this manner and hence sound waves are longitudinal waves.

This is how a longitudinal wave propagates and so does sound.


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Answer 2

Simply because the particles of the medium oscillate in the same direction as the wave propagates. Now you might think, how can a particle oscillate in just one direction ?

Essentially the axis of vibration of the particles is the same as that of the wave propagation.