If the particles of a medium vibrate in the direction of wave motion the wave is called longitudinal. (i) It travels in the form of compression and rarefaction. (ii) A compression (C) is a region of the medium in which particles are compressed. (iii) A rarefaction (R) is a region of the medium in which particles are rarefied. (iv) Examples sound waves travel through 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. (v) These waves can be transmitted through solids, liquids and gases because for these waves propagation, volume elasticity is necessary.
