Make a string phone
You will send a quiet voice through a taut string between two cups. The cups can be far apart, but touching or slackening the string can change what you hear.
- Build
- Starter
- About 20 minutes
Grown-up needed: yes for setup, nearby supervision and clearing spills or loose pieces
What you need
- Two paper cups
- A long piece of string
- A grown-up and a partner
The rule
Keep the string tight.
How to do it
- Ask a grown-up to pinch and hand-tear a tiny hole in each cup base.
- Thread one string end through each hole.
- Tie a large knot inside each cup to hold the end.
- Move apart until the string is gently taut and clear of obstacles.
- Speak softly into one cup while the partner listens at the other.
- Let the string slacken and compare the same quiet words.
Why it works
Your voice creates pressure changes in air inside the speaking cup. Those changes make the cup base vibrate. A taut string can carry the vibration to the other base, which then moves nearby air for the listener. Loose string or contact with another object can reduce the transmitted movement. You may also hear the voice directly through the room, so compare at a distance where a quiet voice alone is difficult to hear.
Make it harder
- Move a little further apart without stretching the string.
- Touch the string gently at its middle.
- Find the quietest voice that works when direct room sound is weak.
Ask Taz
- Why does the string need to be tight?
- Why does touching the string change the sound?
- Why can I sometimes hear without the cup?
For grown-ups
A grown-up prepares the small hand-torn openings and stays with the string. Avoid wrapping it around anyone or pulling hard. The useful comparison is the same voice with different string conditions. Ask at dinner: “How could you tell whether the sound travelled through the string or directly across the room?”
Taz is an AI and can be wrong, so stay close by. Read how safety works on Taz.
Show us yours
Film your hands and what you made, not your face or name. Ask a grown-up before posting anywhere else.
Questions parents ask
Do we need special equipment?
Use the household items listed above. Begin with a small attempt on a clear surface before trying any harder version. The listed time is an estimate, so leave room to rebuild or repeat without rushing.
What if the first attempt does not work?
Notice where the result first changed. Alter one feature, keep the rest similar and try again. An unsuccessful attempt can still give you a useful question.
Do we have to post the result?
No. You can show it to a grown-up at home. Online sharing is optional and needs the permissions in the privacy line above.
More to try
See all Taz Challenges, or look through the science labs. One place for every why. Ask for early access at aitaz.com
Try it in 3D: Sound waves.