The three things you need to make sound

When a tree falls in the forest and no one's there to hear it, does it make a sound? Science teachers and philosophy professors have asked this question of students for years. When you know more about sound, you can try to answer this question for yourself. Read on.

Sound is the result of three things. First, something must vibrate. Your vocal cords vibrate, for example. So does a drumhead when you hit it with a drumstick. A tree hitting the ground also causes a lot of vibrations.

Second, you need something through which the vibrations (sound waves) can travel. Vibrations travel easily through many substances. Air, for instance. They travel even better through water and such dense, rigid things as iron.

Third, these traveling vibrations must be received somehow. Your ears detect the vibrations. Vibrations, once detected, are called "sounds."

Try this: Get a metal fork, and hold it in your hand. With the other hand, gently squeeze two tines together a little. Now let the tines spring back. What happens? The tines wiggle back and forth -vibrate. The vibrations travel through the air to your ear. You detect the vibrations as a high-pitched sound. Try it again. This time, hold the fork upright, with the end resting on a table. Does it sound louder? The vibrations are traveling through the air and the table, now. Try holding the fork on different surfaces - wood, metal, rubber. Which substance makes it sound loudest? That's the substance through which the vibrations travel the best.

When is sound noise, and when is it music? Noise is a mixture of random sound. Music is controlled sound.

A musical instrument is simply a producer of controlled sound. All instruments have something that vibrates: a string on a guitar, for instance; a drumhead; a reed in a clarinet or saxophone. In a trumpet, the player's lips vibrate to create the sound. Musicians control the vibration with frets, keys, slides, and more.

You can make musical instruments, too. All you need is a source of vibration that you can control. A musical instrument can be as simple as a tin-can drum or as complex as a piano.

Now, about that tree falling in the forest. Do you have an answer? The crashing tree creates lots of vibrations, which travel through the air and ground. But by definition, vibrations don't become sound until they are detected. The tree creates vibrations, but you can't really call those vibrations "sound" unless they are heard.

(c) Copyright 2000. The Christian Science Publishing Society