S2.7.4 For the adult
A string telephone
How can a string carry my voice to a friend?
What this chapter teaches
The string itself vibrates and passes the vibration from one cup to the other, so it must be tight and touch nothing. The common mistake is to think the sound runs inside the string like water in a pipe.
Three questions to ask
There is no one right wording. Listen for the idea.
- What do you think the string does when you talk?
- Why does the telephone stop working when the string sags?
- What will happen if a friend pinches the string, and why?
After the chapter, the learner can
- Make a string telephone with two cups and string
- Explain why the string must be tight for it to work
- Explain that the string itself vibrates
What they copy into their notebook
Your voice makes a cup bottom vibrate. A tight string carries the vibration to the far cup. A slack string, or a pinched one, stops it. The sound does not go inside the string.