August 17, 2013

How To Learn More from Making a Tin-Can Phone

Everybody's made a tin-can phone or string phone as a child. They're fun, they work (Can you hear me? Yes!!!), and they're quick and easy to make. But what can we as parents and teachers do to increase the fun and learning? Read on for the basics of how to make a tin-can phone, and then read some ideas for experimenting for more fun and learning!

photo by Florian Seroussi (CC BY-NC-SA 2.0)

Making a string phone is easy. Here's what you need.

  • Two paper cups.
  • A length of non-stretchy string.
  • Something to poke holes in the cups (a sharp pencil will do).
  • Two paper clips (big ones work best).

And here's what you do.

  1.  Poke small holes in the bottom of your cups.
  2. Poke string through the bottom of each hole.
  3. Tie a knot around each paper clip so that the that the paper clips are inside the cups. This anchors the string and prevents it from pulling through the hole in the cup when you pull the string taut.
  4. Decorate as desired.
  5. Enjoy your phone by holding the string tight between two people. One talks, and the other listens. 

 Then experiment!


My students experimenting with string phones
Kids will probably have lots of ideas for experimenting with their string phones, but here are some to get you started.
  • Make a phone for each person and connect them so everyone has an earpiece and a mouthpiece as in the photo above (They could hear each other well).
  • Try different materials: cans or plastic cups instead of paper cups, different kinds of string or twine.
  • Experiment with the string length. How long of a string can you use before the sound is too weak to hear? The video after this list shows people who really push the limits.
  • Do the people on the phone need to be in a a straight line? Try talking with the string going around a wall corner. How about around the leg of a chair.
  • Will the phone work if the string passes under a rug? What if it's wet? What if someone pinches the string?

Can You Hear Me?: The Longest Tin Can Phone Ever.


What do kids learn from string phones?

Kids often understand intuitively why things work if they get hands-on and experiment a lot, but it never hurts to ask the "why" question and see how much they really understand and what needs to be taught. Depending on the interests and abilities of your children, they can learn about sound waves and what media sound travels through, how signal can be dampened and amplified (maybe focused is a better word). They can also learn some engineering when they try to keep the line tense without it ripping through the cup. Kids can learn about real telephones which operate on the same basic concept, except the sound signal is electronic instead of accoustic. (Here's a page about how telephones work.)

Enjoy your string phones, and if you have questions or ideas for further experiments, please leave a comment!

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