Cup Telephones

If you’re looking for something for the kids to do why not try cup telephones?  It’s fun to play with and also teaches kids about sound vibrations and waves.  The best kind of learning – having fun and playing!


cup and string telephone






What you’ll need

It’s really easy to make a cup and string telephone – all you need is two paper or plastic cups and some string!



string threaded through cup






Cut a long piece of string (a few metres) then make a hole in the bottom of each cup.  Thread the string though the hole in each cup and tie a large knot to stop it slipping out.  And that’s it – you’re done!

Using your phone

To use your phone you need two people to stand far enough apart so that the string between the two cups is taut (the string needs to be taut for this to work).  One person speaks into their cup whilst the other holds their cup to their ear.  You should be able to hear what the other person is saying into their cup through yours.

The Science

So why does this work?  Sound travels in waves but these sound waves need something to travel along (air when we speak normally, or the string in our cup telephones).  When you speak into the cup, the sound waves travel along the string and into the cup at the other end allowing you to hear what the other person said.  The string needs to be taut to help these sound waves travel, if it’s slack the sound waves dissipate and don’t travel all the way along the string.  If you put your finger on the string or hold it whilst the other person is speaking you can feel the string vibrating; which is the sound waves.

So why not have a go and then let the kids chat with their new phones?




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