How to Make a Paper Cup Phone

A popular science project for children is to use paper cups, with taut string joining them, to transmit sound. This project demonstrates that sound can travel through the string. The string's vibration as you speak into one of cups is the essence of the operation. As you talk into one cup, the vibration is carried to the other cup. It's always amazing that the device works, and many factors keep it from being used more extensively than just for fun [sources: Denckla, OSU, UNESCO]. Here's how to make a telephone using paper cups and string.

Here's what you need:

Two paperclips
Two paper cups
About 3 yards (2.7 meters) of string
Pin

Here's what to do:

Make a hole in the center of the base of both cups, using the pin.
Tie one paperclip to one end of the string.
Pull the other end of the string through the hole in one of the paper cups. The paperclip should be inside the paper cup.
Insert the free end of the string into the hole in the bottom of the second paper cup. Insert it from the outside of the cup.
Pull enough string through the hole to enable you to tie the second paperclip to the end of the string.
Pull the cups apart so that in each cup the paperclip rests flat on the floor of the cup and the string is taut [source: OSU].

take one cup, and have a friend take the second cup. Walk away from each other until the string is taught you're now ready to use your paper cup phone.