Cup-and-String Telephone
Two paper cups and a length of string turn into a working telephone that teaches how sound actually travels.
By WonderCraft Kids Editorial Team, Editorial team · Updated 1 September 2026
This is one of those classic experiments that still surprises children the first time it works. The string has to stay taut or the message never arrives, so there is a genuine bit of physics to puzzle out, not just a craft to assemble. Setup is five minutes with a hole punch and cups you already own, and cleanup is nothing at all.
What you need
- 2 clean paper or plastic cups
- 3-5 metres of string or thin cotton twine
- A sharpened pencil or skewer
- Two paperclips or small buttons
- Sticky tape (optional)
Step by step
- 1
Push the pencil through the base of each cup to make a small central hole.
- 2
Thread one end of the string through the hole in each cup from the outside in.
- 3
Tie each end around a paperclip or button so it cannot slip back through.
- 4
Give one cup to each person and walk apart until the string is pulled straight.
- 5
Take turns speaking into one cup while the other person holds theirs to an ear.
- 6
Test what happens when the string goes slack, or when someone pinches it mid-way.
What kids learn
Sound as vibration
Talking into the cup makes the base vibrate, and the taut string carries that vibration along its length, which can help children practise thinking about sound as physical movement rather than magic.
Cause and effect testing
Loosening the string or touching it mid-line gives children a chance to see a variable change the result, an early taste of fair testing.
Turn-taking communication
Speaking, then listening, then swapping roles practises the basic rhythm of a real conversation.
Make it easier
Keep the string short, around a metre, and stand close together so success comes quickly before trying longer distances.
Make it more challenging
Add a third cup partway along the line as a listening post, or try connecting two lines to see whether a shared knot lets both work at once.
Safety and supervision
- An adult should push the pencil through the cup base for younger children to avoid a slipped, sharp point.
- Keep the length of string reasonable indoors so nobody trips over it underfoot.
Adult supervision is required for every activity on this site. Read our full child safety guidelines.
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Cup-and-String Telephone
Ages 4-8 · 15 min · no mess
Ages 4+ · No mess
Suggested pin description
Cup-and-String Telephone: Two paper cups and a length of string turn into a working telephone that teaches how sound actually travels. Ages 4+, 20 minutes total, no mess. Full step-by-step instructions and a materials list at WonderCraft Kids.
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Frequently asked questions
Why does it stop working if the string goes slack?+
The vibration needs a tight path to travel along. A loose string absorbs the movement instead of carrying it, so the sound cannot reach the other cup.
Does the type of cup matter?+
Thin plastic or paper cups work better than thick ones, since a stiffer base vibrates less easily.
