Today’s STEAM Activity is the classic cup phone! We rarely talk on the phone at my house anymore. I more often text or FaceTime with friends and family. So my kids are not really familiar with phones (and especially phones with cords) like I was growing up. But that didn’t affect their enjoyment of this simple activity. 


  • Two paper or plastic cups
  • String 
  • Scissors


  1. Measure and cut 20 feet of string. We practiced math while measuring (look in the Math Concepts section below for how we measured the string)

2. Use your scissors, or something sharp to poke a small hole in the bottom center of each cup

3. Poke the string through the hole on the cup and tie a double knot to keep it from coming back through the hole.
Note: A double knot worked well for us because our hole was small. If a double knot doesn’t hold your string inside the cup, try tying the string to a toothpick that is laying horizontally inside the cup to prevent the string from pulling through.

4. Repeat on the second cup, using the other end of the 20′ string

5. Have one person hold each cup and stand 20’ apart (you need the string pulled tight)

Make sure the string is pulled tight, as shown here

6. One person holds the cup to their ear and the other holds it over their mouth. The person with the cup over their mouth can talk quietly or whisper into the cup and the person listening will hear it loud and clear!

7. Switch who is listening and who is talking and try again. We had so much fun with this. We even tried it around a corner so the people talking and listening couldn’t see each other!


  • Science: Sound vibrations can travel through air, solids, and liquids. In this case our sound vibration travels through the string and into the air inside the cup, so you can you hear the whisper from the other side of the room. Sound waves travel better through solid conductors like the string and cup, which is why you hear the whisper more clearly than if you didn’t use this phone. 
  • Math: We practiced simple multiplication while measuring the 20’ of string. Here’s how: we had a 12” ruler. 12”= 1’. We measured 1’ five times, 1’*5=5’. We doubled the 5’ section, 5’*2=10’. We doubled the 10’ section, 10’*2=20’. This was a fun hands-on multiplication lesson for my son!
  • Art: Can you decorate your cups to make them as beautiful as they are functional? It’s like getting a pretty case for your cell phone. 
No matter how you sit or stand, this is a blast!

This is too easy for you to not try right now! Go do it with your kids and let me know how it goes! Do you kids know how to use a phone, or do they only FaceTime like my kids?


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