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Sound

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Author: Janice VanCleave

So You Want to Do a Project about Sound!

Let's Explore

Purpose

To demonstrate the difference in pitch between open and closed wind instruments.

Materials

  • Scissors
  • Flexible drinking straw

Procedure

High or Low

  1. Make a cut through about three-fourths of the center of the flexible section of the straw. Do not cut the straw apart.
  2. Bend the straw at the cut so that the two sections of the straw are at a 90° angle to each other. This is a model of a wind instrument.
  3. Place the end of the shorter top section of straw in your mouth and cover the end of the longer bottom section with your index finger. Blow through the straw and listen to the sound produced.
  4. Remove your finger from the bottom of the straw and blow again. Compare this sound to the first sound.

Results

The sound is higher when the bottom end of the straw is open.

Why?

Each section of the straw is a tube filled with a column of air. When you blow through the straw, the air inside moves forward, causing the air in the lower section to vibrate. Vibrations that travel through the air and other substances are called sound. Air vibrates faster in an open tube than in a closed tube. Since a faster vibration produces a higher pitch (highness or lowness of sound), open tubes have a higher pitch than do closed tubes. In wind instruments, such as the trumpet, clarinet, French horn, and pipe organ, vibrations in columns of air produce sounds with different pitches. If the instrument is closed-for example, by covering the flared-bell opening of a trumpet-a sound with a lower pitch is produced.

FOR FURTHER INVESTIGATION

Moving the slide on a trombone changes the sound produced. Is that because moving the slide changes the length of the tube? A project question might be, How does the length of the column of air in a wind instrument affect pitch?

Clues for Your Investigation

  1. Fill a glass with tap water and set the glass near the edge of a table.
  2. Repeat the investigation, holding the model wind instrument as before.
  3. Place the end of the lower section just below the surface of the water in the glass.
  4. Blow through the straw while you lower and raise the straw in the water. Listen to the sound produced as the straw is moved up and down in the water. From your results, determine how short and long columns of air affect the pitch of sound. You may wish to make a tape recording of the sound to be part of your display.

High or Low

High or Low

REFERENCES AND PROJECT BOOKS

Ardley, Neil. The Science Book 0/ Sound. New York: Harcourt Brace Jovanovich, 1991.

Franklin, Sharon. Power Up! Glenview, ill.: Good Year Books, 1995.

Glover, David. Sound and Light. New York: Kingfisher Books, 1993.

Hann, Judith. How Science Works. Pleasantville, N.Y.: Reader's Digest, 1991.

Jones, Mary, and Geofflones. Physics. New York: Cambridge University Press, 1997.

Murphy, Pat, Ellen Klages, and linda Shore. The Science Explorer. New York: Owl Books, 1996.

Potter, Jean. Science in Seconds with Toys. New York: Wiley, 1998.

Seller, Mick. Sound, Noise, and Music. New York: Shooting Star Press, 1992.

VanCleave, Janice.]anice VanCleave's Physics/or Every Kid. New York: Wiley, 1991.

Wood, Robert W. Sound Fundamentals: Funtastic Science Activities/or Kids. New York: Learning Triangle Press, 1997.

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