Sound travels mostly through air. When a vibrating object moves forward, it compresses the air in front of it by applying force, which creates a region of high pressure that the region is called compression (C).[in figure] when this vibrating region starts moving away from the object, then the vibrating object moves forming a region of low pressure. This region is called rarefaction (R). As the object vibrates that is, moves back and forth with high intensity a series of compressions and rarefactions are generated in the air. Thus propagation of sound takes place in the air.