Step-by-step explanation:
A sound wave is often called a pressure wave because there are regions of high and low pressure established in them medium through which the sound wave travels. The regions of high pressure are known as Compressions and the regions of low pressure are known as Rarefactions . Sound waves are composed of compressions and rarefactions. Compressions are the parts where the molecules are congusted and pressed together. However in the rarefactions molecules are relax and have enough space for expansion. Sound waves are the logitudnal waves and always been defined as the motion of the medium particles parallel to the wave motion.