Describe, with the help of a diagram, how compressions and rarefactions are produced in the air near a source of the sound.

When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called a compression as shown in the figure below:

When the vibrating object moves backwards, it creates a region of low pressure called rarefaction (R), as shown in the above figure. As the object moves back and forth rapidly, a series of compressions and rarefactions are created in the air.