Question

what is the nature of sound waves

Answer 1

NATURE OF SOUND: Sound is a type of mechanical wave which requires a medium to be transmitted. Sound waves are called longitudinal waves too. This means that the medium particles of sound wave move  parallel  to the wave motion. Sound cannot travel through vacuum.

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Answer 2

Sound waves in air (and any fluid medium) are longitudinal waves because particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave moves. A vibrating string can create longitudinal waves as depicted in the animation below.