Sound, a form of energy, is all around us. Even in a quiet place, you can hear sounds. What makes sound, how does it travel, and how do we hear sound are all questions that are frequently asked. From the slight humming of the computer screen to the screaming sounds of a rock concert, all sound is produced in the same way - sound energy causes vibrations.

All matter is made of molecules. Molecules can be tightly packed together as in a solid or they can be loosely packed together as in a liquid or gas. When energy strikes the molecules of matter, it causes the molecules to vibrate back and forth, producing a wave that transmits sound energy. The closer the molecules, the more easily sound can be transmitted. Since molecules in a solid do not move very far and bounce back very quickly, a solid is an excellent transmitter of sound. Liquids do not transmit sound very well, but gases are the poorest transmitters of sound.

Sound travels quickly in air at nearly 340 meters per second but can travel through steel at about 5,200 meters per second. Even at such high speeds, sound travels a lot slower than light. Think of the last time you experienced a thunder and lightning storm. You saw the lightning flash before you heard the thunder because light travels over a million times faster than sound in air! The temperature of the medium can also affect the speed of sound. As the temperature of a medium increases, the speed of sound also increases.

When you go to a rock concert, you may have to cover your ears because the sound is so loud. This loudness is called intensity. Intensity is measured in units called decibels. A soft sound that can barely be heard has an intensity of 0 decibels, while a rock concert has an intensity of 120 decibels. Sounds of 120 decibels or greater can cause people pain and ear damage.

When sound waves enter the outer ear, they move through the ear canal and strike a tightly stretched membrane called the eardrum (the tympanic membrane). The vibrating air molecules cause the eardrum to vibrate very much like a musical drum. From the eardrum, the vibrations enter the middle ear, which contains the three smallest bones in the body. The first bone, the hammer, picks up the vibrations and passes them to the anvil. The anvil passes them on to the stirrup, and the stirrup passes them on to another membrane that transmits the vibrations to a liquid-filled inner ear. The vibrations are then channeled into the cochlea. In the cochlea, there are hundreds of special cells attached to nerve fibers. The vibrations are converted to electric impulses that the nerve fibers transmit to the brain, and the brain interprets them as sound.

Hearing loss is the most common physical disability in the United States. At least 15 million Americans suffer from a noticeable hearing loss and about 2 million of these people are deaf. Some people are born deaf, but many lose some or all of their hearing due to damage caused by loud noise. It is very important to protect your hearing. Even music with an intensity above 85 decibels can cause ear damage. The best way to protect your hearing is to avoid being exposed to loud sounds, especially for prolonged periods of time. If you must be exposed to constant loud noise, wear earplugs to help reduce the damage. Many great people in both history and the present are deaf, but I am sure that they would all agree that it is better to take care of your hearing than to lose it.