Why do we call sound waves longitudinal?
 
 The particles of the medium through which sound travels vibrate in a . of the wave's propagation. Hence, sound waves are called longitudinal waves.
 
Sound waves are because the particles of the medium to vibrate in the direction which is  to the direction of the propagation of the sound waves.
 
The particles in the medium oscillate  in the case of .
Compressional waves are also called as .