Make a Paper Cup Phone

It seems everywhere you look people are talking about STEM activities for kids.   Not only do the activities get kids thinking about science, technology, engineering, and math, but kids genuinely love STEM challenges.

This week we had fun with a classic STEM activity: making a paper cup phone, something I remember doing as a child.

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Making a cup phone is a fun way to learn about the science of sound.  You might also want to try this simple sound experiment.

Paper Cup Phone

Materials Needed: 

• 2 paper cups
• 20 feet of string (We used yarn.)
• Sharpened Pencil
• 2 Paper clips (optional)

To make your own cup phones, use the tip of a pencil to poke a small hole at the bottom of each of your two cups.

Next, thread the string through the hole of one cup.  We just tied a knot in the yarn 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.

Pull the string through the bottom of your second cup, securing it with an knot on the inside, too.  (See photo above.)

To use your cup phones the string must be kept taut.  When one person whispers in their cup, the other should be able to hear their voice through their own cup.

My daughter was thrilled to hear my voice being whispered in her ear from over 20 feet away!

You can even try whisper singing into the cup, turning it into a musical STEM activity.  

Related post: STEM Challenge: Build a Boat that Floats

Why does the string and paper cup phone work?

Sound waves can travel through air, solids, and liquids.

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.

Take your cup phone activity further!

Have your child try one or more of the following extension activities:

• Use a longer piece of string.  Does the homemade phone still work if the string is 40 feet?  How about 60?
• Try making the phone with plastic cups or tin cans.  Which phone works the best?
• Replace the string with wire.  How does this affect the phone?

You kids will have fun learning how to make a paper cup phone! 

You may also like:

• Music STEM 
• STEM Challenge: Design a Boat that Floats
• STEM Challenge: Craft Stick Catapults
• STEM Challenge: Build a Stuffed Animal Chair
• Old-Fashion Fun with Tin Can Stilts