by Tom Harris

Ear diagram courtesy NASA
Your ear is a delicate and detailed sensory organ. 

Your ears are extraordinary organs. They pick up all the sounds around you and then translate this information into a form your brain can understand. One of the most remarkable things about this process is that it is completelymechanical. Your sense of smell, taste and vision all involve chemical reactions, but your hearing system is based solely on physical movement.

In this article, we'll look at the mechanical systems that make hearing possible. We'll trace the path of a sound, from its original source all the way to your brain, to see how all the parts of the ear work together. When you understand everything they do, it's clear that your ears are one of the most incredible parts of your body!

To understand how your ears hear sound, you first need to understand just what sound is.

An object produces sound when it vibrates in matter. This could be a solid, such as earth; a liquid, such as water; or a gas, such as air. Most of the time, we hear sounds traveling through the air in our atmosphere.

When something vibrates in the atmosphere, it moves the air particles around it. Those air particles in turn move the air particles around them, carrying the pulse of the vibration through the air.

To see how this works, let's look at a simple vibrating object: a bell. When you hit a bell, the metal vibrates -- flexes in and out. When it flexes out on one side, it pushes on the surrounding air particles on that side. These air particles then collide with the particles in front of them, which collide with the particles in front of them, and so on. This is called compression.

When the bell flexes away, it pulls in on the surrounding air particles. This creates a drop in pressure, which pulls in more surrounding air particles, creating another drop in pressure, which pulls in particles even farther out. This pressure decrease is called rarefaction.

In this way, a vibrating object sends a wave of pressure fluctuation through the atmosphere. We hear different sounds from different vibrating objects because of variations in the sound wave frequency. A higher wave frequency simply means that the air pressure fluctuation switches back and forth more quickly. We hear this as a higher pitch. When there are fewer fluctuations in a period of time, the pitch is lower. The level of air pressure in each fluctuation, the wave's amplitude, determines how loud the sound is. In the next section, we'll look at how the ear is able to capture sound waves.

(Source: How stuff works?)