How to Make Phones With Strings & Cans


Making a string-and-can-phone is a great summertime activity for would-be spies and on-the-spot reporters. A couple of cans, a stretch of string and a little imagination is all you need to create a communications system that, although lacking in fidelity, is full of fun and entertainment. There are lots of ways to experiment with the physics of direct wave transmission, the principle demonstrated with the string-and-can-phone. Changing the size of the cans and the diameters and lengths of the string, for example, will bring you different sound qualities.

Things You'll Need

  • Two empty soup cans
  • Tightly wound string
  • Awl
  • Poke a hole in the bottom of each can with the awl to receive the string. Try to make a very small hole -- the string should just barely fit into the can.

  • Poke one end of the string up through the bottom of one of the cans, pushing it far enough into the can that it extends out of the other end. Tie a very tight knot in the extended end of the string. The knot must be big enough the string can't be pulled out of the bottom of the can.

  • Thread the other end of the string into the other can. Tie a tight knot in the loose end of the string as you did with the first can. The end result should be two cans firmly tied on either end of the string with their bottom, closed ends facing one another.

  • Move the two cans apart until the string is pulled taut between them.

  • Have one person speak into one of the cans. As long as the string remains taut, the other person should be able to hear the voice.

Tips & Warnings

  • Sound waves will travel from one can through the string to the other can. The string and cans vibrate to the waves, recreating the sound. Tight connections between the cans and the string will ensure a good sound wave transmission.
  • The size of the can has a direct impact on the success of the wave transmission. Tall cans, like soup cans, will provide the best sound. Flat cans, like tuna cans, don't have as much surface to vibrate, while large cans, like coffee cans, have too much surface.
  • Similarly, the quality of the string has a lot to do with how well the sound will travel. Twine, yarn, or other loosely-wound strings won't transmit waves as well as kite string or thin cord.
  • Wash out the cans thoroughly before using them.
  • Watch for and file down any sharp edges on the cans.

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  • Conn Iggulden and Hal Iggulden; The Dangerous Book for Boys, 2006
  • Photo Credit Stockbyte/Stockbyte/Getty Images
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