Demonstration: Making a Pie Pan Speaker

©1995 The Regents of the University of California

by Regan Lum

Purpose:

In this lab, we will make and play with a communication device made with two paper cups and a string (fig. 1). When you talk into the cup, your voice causes the bottom of the cup to vibrate at the same frequency as your voice. The vibration is carried along the string to the bottom of the second cup. This causes the air in the second cup to vibrate and the sound is reproduced.

figure 1

Materials:

• 2 - cups
• toothpick
• kite string
• secret messages

Procedure:

1. Take a short piece of toothpick and poke a hole in the bottom of a paper cup.
2. Thread a piece of string through the bottom of the cup and tie the short piece of tooth pick on the inside of the cup (fig. 2).
3. Have your lab partner run the string down the hallway and repeat steps 1 and 2. Please stagger the distances between the cups of the different lab teams.
4. Pull the string taut, but do not rip the string out of the bottom of the cup. You and your lab partner may now open you secret massage.
5. Read and record the secret messages.
6. Try another lab team's walkie talkie with a different length string and compare the sound quality.

figure 2

Data:

1. What was the approximate length of your string? Does the distance make any different in the loudness and clarity of the message?
2. What were your secret messages?

Conclusion:

1. How is sound transmitted from one cup to another?
2. How does the length of the string affect the sound quality? Compare the loudness and the clarity

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