String Telephones – Conference Calls

Engineering Science
Time 45 minutes
Age 7 & up
Group Size 4 or more
Tags Cups, Sound, String,   more...
Teamwork Telephone Vibration

Can you make a telephone using only cups and string...and talk to more than one person at once?

Engineering challenges like this one help children develop problem solving, observation and teamwork skills and much more. In this challenge, your students will learn about properties of different materials and the transmission of sound as they work to develop a multi-line phone system with simple materials.


This is a follow-up to the String Telephones activity – try that activity first if you have not yet done so.

If you have younger children, you might choose to poke holes in the cups ahead of time. If you are using metal cans, you should do this despite the age of your students and make sure that there are no jagged edges.

String Telephones – Conference Calls

Suggested Materials

  • Different kinds of cups (paper, plastic, Styrofoam, metal cans, large, small, etc.)
  • Several different kinds of string (cotton, kite string, thread, gimp, dental floss, etc.)
  • Paper clips (100)
  • Scissors
  • Sharp pencils or small nails (for poking holes in the cups)

Make it Matter

Opening Discussion

Refer to your last experience in the String Telephones activity. How many children could listen in to the conversation at once? Is it possible to make a telephone that has 3 lines?

The Challenge

Challenge your children to create their own 3-way telephone system.


Make it Happen

Doing the Activity

  1. Children should now work in teams of 3.
  2. Offer the same materials as the first session, and have each team decide which type of cup and which type of string they’d like to use.

Make it Click

Let’s Talk About It

After 10–15 minutes of activity, if every team has made and tested at least one phone system, stop your students and bring them together to share their observations with each other. This discussion should last no more than a few minutes. Did anyone have a successful 3-way call? Have them demonstrate the use of their phones. Is there more than one solution? Are there any ideas any teams have that they haven’t tried yet?


Make it Better

Build On What They Talked About

Send them back to experiment more.


  • There are several ways to accomplish a 3-way call, such as:
  1. Each cup has 2 strings coming out of it, making a triangle with the 3 cups;
  2. The ends of the strings coming from each cup can be tied together in a knot;
  3. 2 cups can have one string coming from them, each leading to a third cup, which will serve as a “relay” to the other 2 cups; and
  4. A second string can be tied to the string between 2 cups—this third listener is “tapping in” to the original telephone design.
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