Good vibrations - The story of how sound is created

February 15, 2008|By LISA TEDRICK PREJEAN

My daughter and I are enrolled in the Maryland Symphony Orchestra's "Symphony Saturdays" program for children in first through third grades. It is a wonderful program that introduces children to the instruments used in an orchestra.

I was familiar with the program because my son was enrolled in it a few years ago. He enjoyed hearing the sounds of the various instruments, meeting the musicians and experimenting with music.

The musicians relate well with children.

At the start of last Saturday's program, one of the musicians asked "What is sound?"

I wondered if the children would answer correctly. This concept was included in a science unit I recently taught to my third-graders, but I wasn't sure if other children attending the MSO program had had similar lessons.

What is sound? How would you describe it? One word comes to my mind.

After the musician asked the question, a few children guessed what they thought sound is. Then a little boy in front of me raised his hand and gave the correct answer.


"Vibration," he confidently said.

My daughter looked at me with a wide-eyed look and said, "I was going to say that."

I whispered back, "Well, you would have been right."

If you gently place your index and middle fingers on your throat and hum, you will feel the vibration, and you will hear the sound.

Sound is vibration, a back-and-forth movement of molecules of matter. Sound vibrations can travel through solids, liquids or gases.

Which one of the three do you think sound can travel through fastest?

Think about this. Two beavers are building a dam. One swims across the stream to gather some twigs. The other stays close by the dam. Suddenly, a human appears. The beaver closest to the dam wants to warn the other beaver so he swats the water with his tail. Where is the best place for the beaver to be in order to hear the sound, on the bank or in the water?

If the beaver is on the bank, the sound has to travel through air. It would reach him faster if he is in the water because sound travels faster through liquids than gases.

What about solids?

Think about what happens when you tap your pencil on a desk. You hear the sound because it travels from the desk, through the air to your ear.

But let's say you get tired and you rest your head on the desk while you still are tapping your pencil. The sound suddenly becomes louder. Sound travels faster through solids than gases.

In a nutshell, sound travels fast through air, faster through liquids and fastest through solids. The closer together molecules are, the more quickly they bump each other when influenced by sound vibrations.

Sounds are sometimes absorbed, or taken in, by various surfaces. Carpets, curtains, certain types of tiles and other coverings can help to absorb sound.

Sometimes sounds are reflected. They bounce off a surface. When a sound is reflected from a surface and returns to the source, it is called an echo.

In order to hear an echo, you must be standing at least 55 feet away from the object that is reflecting the sound.

Sound vibrations enter the ear, pass through the ear canal and hit the eardrum. The membrane of the eardrum vibrates and causes vibrations in the three smallest bones in your body - the malleus, the incus and the stapes. These bones are commonly called the hammer, anvil and stirrup because that's what they look like.

The mechanical vibrations of these bones cause vibrations in the fluid-filled cochlea - a coiled part of the ear - stimulating tiny, hair-like cells. (Coincidentally, the word cochlea comes from a Greek word meaning "snail," because the cochlea looks like a snail.)

The hair cells in the cochlea convert the vibrations into electrical impulses, and nerves carries these impulses to the brain. Our brain assembles the impulses into sounds. That's when we hear what was said, sung, played, hit, rubbed, plucked or blown.

It's such an amazing process, and yet children seem to grasp it so easily.

I think they heard every word I said.

Lisa Tedrick Prejean writes a weekly column for The Herald-Mail's Family page. Send e-mail to her at

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