STEM Club - Cup Phones

Lesson: Science

Make Your Own Telephone!

Why not colour a unique design on your paper cups first? Then follow the instructions   below to start your investigation.

1. Take a sharp pencil and make a small hole in the bottom of each paper cup.

2. Next, thread the string through the hole of one cup.  You could just tied a knot in the string on the inside of the cup to keep it in place.  If the string keeps slipping through the hole you can tie it to a paper clip to help keep it in place.

3. Pull the string through the bottom of your second cup, securing it with an knot on the inside, too as shown in the picture.

4. Now it’s time to test out your telephone. Find a friend and give them one end of the telephone. Now walk away from each other until the string is taut (not floppy or loose!). Take turns to whisper into the cup and see if the sound travels.

Telephone Challenges—Remember to change just one variable at a time and see what     happens!

¨ Loosen the string so it is not taut. Does the volume of sound change? Why do you think this is?

¨ Change the length of string. You can cut the piece of string you started with and then swap it for the longer length of string provided—what happens to the sound?

¨ If you have extra string at home, how long of a piece of string can you use before you stop being able to hear the whispering into the other end of the telephone

¨ Have someone place two fingers on the string while it is being pulled taut. Does this affect the volume of the sound?

So how does it work?

When you speak into the cup, the vibrations are transmitted into the string.  They continue to travel through the string, as long as it is held taut, to the receiving cup.  There the vibrations are transmitted to the air in the cup, around the listener’s ear, allowing the whisper to be heard.

Because the cup and string are solid, and solids actually carry sound waves better than air, the whisper can be heard much clearer than if you were to just whisper into the air from that distance.