Build a String Telephone

Ever wonder if you can actually use tin cans to make a telephone? Let’s try it and see!

What you need:

• Paper or Styrofoam cups
• String
• Toothpicks

Try This:

1. Tie a toothpick on each end of a length of string.
2. Poke the toothpick through the end of the cup. Pull the string tight so the toothpick rests on the inside bottom of the cup. Put one cup at each end of the string. (You may want to experiment with different cups and strings to see what works best.)
3. Hold the string tight and talk into one of the cups. The person at the other end should be able to hear you. Why does the string have to be tight?
4. Try to make a party line by tying a third string and cup onto the middle of the string. Can everybody talk to everybody else?

What’s going on?

Sound waves need something to travel through. Usually they travel through air, but they can travel much faster and farther through a string. The string has to be tight or else the sound wave can’t travel through it. The cup helps to amplify the sound on the other end.