If the particles of a medium vibrate in the direction of wave motion the wave is known as longitudinal.

a)      It goes in the form of compression and rarefaction.

b)      A compression (C) is a region of the medium in which elements are condensed.

c)       A rarefaction (R) is a region of the medium in which elements are rarefied.

d)      Examples sound rays go by air in the form of longitudinal waves, Vibration of air column in organ pipes are longitudinal, Vibration of air column above the surface of water in the tube of resonance apparatus are longitudinal.