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SOL:Science:
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Purpose: To demonstrate the difference in pitch between open and closed instruments
Materials:
1) scissors
2) ruler
3) drinking straw
Procedure:
1) About 2 inches (5cm) from the end of the straw, make a cut through about ¾ of the straw. Do not cut the straw apart.
2) Bend the straw at the cut so the two sections are at a 90º angle to each other. This is a model of a wind instrument
3) Place the end of the shorter section in your mouth and cover the end of the longer section with your index finger.
4) Blow through the straw and listen to the sound produced.
5) Remove your finger from the lower section and blow again. Compare this sound to the first sound.
NOTE: Keep the model for the experiment that follows
Results: the sound is higher when the end of the lower section is open
Why? :
Each of the straw sections 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. Air vibrates faster in an open tube than in a closed tube. Since a faster vibration produces a higher pitch, open tubes do 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 opening of a trumpet – a sound with a lower pitch is produced.