Tin Can Telephone
Connect two cups with string and test how far sound travels and what changes the quality.
- Age3 to 6 years
- Time15 to 30 minutes
- EnergyModerate
- CostFree
- WhereIndoors or out
- Prep5 min
Thread string through two cups, hold them taut, and speak into one while your child listens at the other. Then experiment together: what changes the sound? Longer string? Touching the string? A different cup material?
How to do it
- Choose two identical cups: paper, plastic, or metal (metal cans give the clearest sound but require adult-only hole-punching; paper or plastic cups work well with a pencil-poke hole).
- Use a sharp pencil or skewer to make one small hole in the base of each cup (parent does this for under-5s).
- Thread one end of a long piece of string (start with 2-3 metres) through the hole in each cup. Tie a knot on the inside of each cup so the string can't pull back through.
- Hand one cup to your child and hold the other yourself. Walk apart until the string is taut: it must not sag or touch anything between the cups.
- Speak quietly into your cup while your child holds theirs to their ear. Then swap. Ask: "Can you hear me? What does my voice sound like?"
- Experiment: touch the string in the middle (sound stops), let it sag (sound stops), try a longer string, try whispering versus normal voice.
What you need
- Cups
- String
- Sharp pencil or skewer
- Open space
Signs it is working
Your child clearly hears your voice through the cup and expresses surprise or delight. They swap roles and speak into their cup. They want to test what changes the sound: touching the string, walking further apart: showing curiosity about the mechanism
If it is not quite clicking
No sound transmits at all: The most common cause is a sagging string: the line must be held taut with no contact with furniture, walls, or the floor between the two cups. The knot inside a cup isn't holding: Check that the knot inside each cup is large enough that it can't slip back through the hole. The string keeps sagging because the space is too small: Try a diagonal across the room (from a sofa armrest to a doorway) rather than a straight line. Using tin cans with sharp edges: Sand or tape any sharp edges around the hole before the child handles them; this activity requires elevated supervision at the hole-making stage regardless of cup material
Make it yours
Younger, 2-3 years: Parent does all the construction and holds their cup; child just listens and talks. The "magic" of hearing a voice through the cup is enough. Skip the experiments. Older, 5-6 years: Introduce the word "vibration": the string carries your voice because it vibrates. Challenge them to test a third variable (what if you use wool instead of string? What about a longer string?). Siblings: Three-person versions don't work well (string splits); each pair makes their own telephone and they "call" across the room.
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