Tin Can & String Telephone: A Simple STEM Experiment

What transmits sound better: recycled soup cans or plastic party cups?

two clean soup cans with string running through them making a tin can telephone

Experimenting with tin can or plastic cup telephones can be a great boredom buster for kids! Kids growing up in the smartphone generation will be amazed at how something as simple as STRING can transmit sound.

Granted, tin can phones aren’t the most practical communication device. Since the line between cans needs to be held taut to transmit sound, you’re unlikely to “place a call” farther than down the hall or across the back yard.

Unless…

Worlds Longest Tin Can Phone

The Guinness Book of World Records says the worlds longest FUNCTIONING tin can phone was made in Japan in August 2019. It went 242.626 meters, or 796 feet! That’s almost three football fields long! Sadly, there’s no details on how the phone was made or what materials they used.

supplies used to make a very long tin can and string telephone
Click the Image to Play over on YouTube

If you want a little inspiration before setting up your own backyard experiment, check out this video from 2013 when a few friends set up a tin can phone between two houses over 650 feet apart! Not only is their experiment amazing, but the video is well made and entertaining.

Lots of YouTubers have tried their own tin can phone experiments. Spoiler alert: the Danocracy might SAY they made the world’s longs phone at 1000 feet…but it didn’t work. Does that make it click bait? ¯\_(ツ)_/¯

supplies need to make a tin can telephone: 2 cans (soup are shown), string, a hammer and a nail.

Supplies for a String Telephone Experiment

First…I want to point out that “tin cans” these days are actually made of steel. Steel cans are lined with either tin or plastic to prevent rust and keep your food tasty. But we still call them “tin cans” out of habit.

A basic string phone can be made with supplies you’re likely to have around the house. If you want to get really scientific, try out a variety of “receivers” and types of string.

You’ll need two cans or cups. These can be recycled soup cans, plastic party cups or paper cups. The cups will help transmit the sound — keep notes and find out which cup works best!

Note: We found Styrofoam cups to be pretty horrible. The material is too fragile when you pull the string tight. Little kids are likely to rip a hole in them.

You’ll also need string, and lots of it! The guys in the 2013 video used nylon twine, which is pretty stout. Of course they were also running their line over 650 feet. Cotton string, fishing line and ordinary twine also work. What else can you try out? Yarn? Dental floss? Sewing thread?

Make a String Telephone for Kids

Make a String Telephone for Kids

Active Time: 10 minutes
Total Time: 10 minutes

Conduct an experiment in SOUND with this old school craft!

Materials

  • 2 Clean Cans or Disposable Cups
  • String (at least 25 feet)
  • Washer or Paper Clip (optional)

Tools

  • Hammer
  • Nail

Instructions

  1. If using a recycled can, work on a a sturdy surface, like a work bench if you have it or a thick plastic cutting board. (Don't hammer on your nice kitchen table!)
  2. Lightly hammer a nail into the center of the bottom of the can. You just need a hole big enough to poke your string through.
  3. If using a disposable cup, you should be able to poke a hole in the bottom of the cup without a hammer!
  4. Repeat for both cans or cups. You'll need two!
  5. Push the string from the outside of the can--be careful, metal cans could have sharp edges.
  6. Pull the string through the can. Tie a large knot in the string. It needs to be big enough to prevent the string from coming out.
  7. If your hole is too big, or the string too narrow, tie the string to a washer or paper clip to keep it in place.
  8. Repeat for the other can or cup.

Notes

If you're running this as an experiment, make several phones at once with a variety of materials. You can also try a can on one end and a cup on the other. Which work best? Record your results!

How to Use Tin Can or Cup Telephones

Once you’ve made your telephone, you’ll need two people to run the experiment. Have each person take an end and walk apart until the string is TIGHT. One person then holds the can or cup to their ear while the other talks into their can or cup.

Mother and daughter using a tin can phone

Ideally, you’ll want to stand far enough apart that you can speak normally into the phone and not be heard by the other person. If you can’t get THAT far apart, try a whisper!

Pet Peeve: A lot of stock photos (and blogger photos!) of people using tin can phones are misleading. They show people with the string dangling loosely between the two ends. This WILL NOT work. No wonder that guy looks confused.

They also show people standing right on top of each other. You need a bit of distance for this experiment to really work.

Photos of tin can phones that will not work -- the string is not held tight.

Record Your Experiments

Level up your tin cans from “just another craft” to a fun STEM event by making several phones or swapping out materials. Record your results!

How far did you get? How clearly did you hear the words? Which one was easier to make?

Jot down your findings on a scrap of paper, or use the free printable below. You can also record your experiment using a Voice Recorder app on your smart phone for later comparison.

sheet to record results from a string phone experiment