Pitch Switch

INTRODUCTION

Humans can hear a wide range of loudness, from the very quiet sounds of a whisper to the loud roar of a jet engine. We can also hear extremely small differences in the highness and lowness of sounds. This characteristic of sound is called pitch. Some musical instruments, such as a piano or harp, have strings, each of which plays a different pitch. The longer the string, the lower the pitch.

MATERIALS

• 1 paper cup
• 1 push pin
• 1 long rubber band
• 1 paper clip
• 1 wooden ruler
• Tape
• Scissors

WHAT TO DO

1. Use the pushpin to carefully poke a hole in the center of the bottom of a cup.
2. Cut a long rubber band. Thread one end through the hole in the cup. Tie two or three knots in the end of the rubber band so it will stay securely in the cup.
3. Tape the cup to the ruler so that the bottom of the cup is on about the 2 cm line.
4. Tie a paper clip to the free end of the rubber band. Stretch the rubber band to the other end of the ruler. Tape down the rubber band and hook one arm of the paper clip under the end of the ruler so the rubber band stays securely attached to the end of the ruler.
5. Hold the open end of the cup to your ear. Pluck the rubber band once. Press the rubber band down onto the ruler near the end opposite the cup. Pluck the rubber band again.
6. Press the rubber band down as you move your finger closer and closer to the cup. Pluck the rubber band each time you press down on the rubber band. Notice the difference in the sounds you hear when different parts of the rubber band are vibrating.

QUESTIONS

1. How was the sound different when you pressed the rubber band down to the ruler?
2. How does changing the length of the vibrating part of the rubber band change the pitch of the sound?
3. How do you think the sound will change if, instead of pressing the rubber band down closer and closer to the cup, you press the rubber band down further away from the cup? Try it!
4. How is question 3 similar to the way a guitar player can change the pitch of a string on a guitar?

SUMMARY

Very rapid vibrations produce high pitch sounds and lower pitch sounds are the products of slower vibrations. The pitch switch is able to produce a variety pitches because the amount of the rubber band used to produce the sounds can be varied. When a long portion of the rubber band is plucked it vibrates slowly and a low sound is heard. When a shorter piece of the rubber band is plucked it vibrates more quickly and a higher note is heard. There is a difference in the speed of the vibrations when longer or shorter portions of the rubber band are plucked because of the difference in mass of the portions. A heavier piece of rubber band requires more force to make it vibrate, so it vibrates more slowly than a shorter piece would if plucked with the same force.

SOURCE

"The Best of Wonders Science: Elementary Science Activities." American Institute of Physics, Delmar Publishers: Albany, 1997, p. 455.

© S. Olesik, WOW Project, Ohio State University, 2000.