Changing the Pitch of Sound

Research Questions:

• How can the pitch of a sound be modified?
• How does the rate of vibrations affect the pitch of sound?

Are all sounds alike? Of course not! Some sounds are loud while others are soft. There are high-pitched sounds and low-pitched sounds. The pitch of a sound is based on how high or low the frequency of a sound which has to do with how fast or slow the vibrations are. Lower pitch sounds are produced from slower vibrations while higher pitch sounds are produced from faster vibrations.

Materials:

• Zipper
• Ruler
• Scissors
• Paper clip
• Paper clip
• Tape
• Rubber band

Experimental Procedure:

1.  Can a zipper produce different sounds? Try it! Zip the zipper up and down very fast. Listen to the sound. Now zip the zipper up and down slower. What do you notice about the sound? Record your observations. (See sample chart.)
2. Carefully use scissors to punch a small hole in the bottom of a cup. Then cut the rubber band so that it becomes one long piece.
3. Tie the paper clip onto one end of the rubber band. With the cup upside down, thread the rubber band up through the cup and the hole in the cup. The paper clip should be held inside the cup with the rubber band coming out through the hole. 
4. Tape the 12-inch end of the ruler to the side of the cup so that it is standing up beside the cup.
5. Now stretch the rubber band over the end of the ruler and tape it to the other side. Pluck the rubber band and observe the sound. Record your observations.
6. Remove the tape and pull the rubber band over the ruler even more to make it tighter. Pluck the rubber band again and observe the sound. Record your observations. Was the sound different this time?
7. Experiment with the rubber band by pressing one finger against the rubber band and ruler at the 1-inch mark and plucking it with the other hand. Try this at different lengths…3-inch, 5-inch, 7-inch. Record your observations of the sounds at each.  

Terms/Concepts: Sound; Vibration; Pitch; Frequency

References:

a.   http://scifiles.larc.nasa.gov/text/kids/Problem_Board/problems/sound/sound_waves2.html b.    http://www.sciencekids.co.nz/gamesactivities/changingsounds.html (Good virtual demonstration)