To understand how the ear performs its tasks, we need to know a little about the nature of the stimulus energy for audition. We call this energy the sound wave.

To hear, the ear must detect changes in the air pressure surrounding the eardrum. What causes these changes in air pressure?

Sound is a mechanical form of energy, generated by an object vibrating in our environment. The vibrations cause the molecules in the surrounding air to move back and forth at the same rate as the vibrating object.

In this example, when the tines of the tuning fork move to the right, they compress the air molecules on that side, producing a region of high pressure. When they move to the left, the air molecules on the right side are then pulled away from each other, producing a region of low pressure. These alternating regions of high and low pressure move away from the tuning fork in all directions like ripples on a pond.