Question

why sound wave is call longitudinal wave

Answer 1

Sound waves in air (and any fluid medium) are longitudinal wavesbecause particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave moves.

Answer 2

Sound wave is called longitudinal wave bcz particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave moves. A vibrating string create longitudinal wave.