Experiments for Kids: The Paper Cup Telephone

Reviewed & Fact Checked  by Rebecca Carlock

One of the most commonly referenced experiments in Hollywood film history, the Paper Cup Telephone experiment is one of those scientific explorations that kids simply need to experience for themselves.

Anyone who’s seen the typical Hollywood boy-meets-girl movies has probably already seen this experiment at work: a boy in one room and his girl best friend in the other, paper cups in hand linked together by a long string as they talk to each other.

At some point, you may have found yourself asking yourself if it actually worked. Well, just to give anyone out there who needs it some confirmation, there’s actually a lot of science behind the experiment.

Fittingly, as STEM learning becomes increasingly prominent as the national standard for early childhood, elementary, and high school education, it seems just appropriate that the popular experiment be given a second look and revisited.

To experience the sweet science of the paper cup telephone experiment firsthand, here is a step-by-step guide on how to conduct it yourself for your kids to enjoy.

The Paper Cup Experiment

Debunking the notion that STEM education requires sophisticated machinery and gadgets to become effective, the Paper Cup Experiment requires only household materials and minimal complexities.

Here are some of the things you need to facilitate your own Paper Cup Telephone experiment:

  • Two paper cups
  • 20 feet of string
  • Pencil
  • Two paper clips (optional)

For the string, you can use some yarn, if it’s available. The pencil should also be sharpened for this experiment as it will be used for punching holes into the cups. The most important part of this experiment, of course, is a partner with which you’ll be testing the activity. This experiment, after all, works best for two participants.

Here are the steps you need to follow to create the actual phones for the experiment:

  1. The first step, after you prepare the materials, is to take the pencil to poke small holes into the base of each of the two cups. Poke just one hole at the center of each cup.
  2. Next, take the first cup and run the string through the hole.
  3. Be generous about the string that you run through the cup as you will need to tie a thick knot with it; thick enough to hold in place so that if ever the string is pulled from the opposing side, the knot holds its place firmly at the bottom of the cup. If ever the knot can’t hold the string in place and keeps slipping through the hole, you can consider tying it to a paper clip to help hold it in place.
  4. Once you secure the string and know for one cup, thread part of the string through the bottom of the second cup and secure it the same way you did for the first one. In essence, the cups must both be firmly secured with the string as it is vital for the experiment to work.

In order to make your paper cup telephones work, the string must be secured onto the bottom of the material firmly. Based on the science at work here, when a person whispers or says something through their respective cups, the person holding the other end of the mechanism should be able to hear their voice through their own cup. According to the materials recommended above, the best results should be one person being able to hear the other from about 20 feet away.

Experimenting and Activity Variation

There are a couple of things you can do to make things even more interesting. To fully sate your kids’ scientific appetite, you can manipulate some of the variables to see if it changes the results of the initial experiment.

The first variation you can administer is whispering songs into the cup instead of just actual conversation. This gives this STEM project a performative art element, a facet in learning that has been found to help child development. It can also be an interesting sensory experience for the kids as singing can provide stimulation to auditory receptors in the ears.

As mentioned, you can also manipulate several variables to see how they would affect the results. Start by using a longer piece of string. Does this increase the volume of the person’s voice? Does it reduce its volume? Does it change anything? Does the telephone cup still work at 40 feet or 60 feet of string?

What if you turn the plastic cups into tin cans? Does the plastic phone provide better acoustics? Does it yield louder sounds?

What if the strings become wires? Does it still sound the same at 20 feet? Does the sound change at 40 feet or 60 feet?

With these changes, you and your kids can change the variables all you like and see how it changes the results. It would be a complete and comprehensive STEM experience for both you and your kids.

The Science Behind Paper Cup Telephones

Now it’s time to deconstruct this scientific showcase and break it down into digestible concepts? How and why does the string and paper cup phone work? The simple answer is: sound can travel through air, solids, and liquids.

Sound travels through things as waves. When someone speaks into the cup, the waves are funneled by the shape of the cup and are transmitted through the string. The waves continue traveling through the string and into the receiving cup. The vibrations then move through the air in the second cup and around the listener’s ear, enabling the slightest sounds to be heard.

One thing to note is that solids carry sound better than air does. Since the string and cups are solids and are connected, it’s easier for the soundwaves to travel through the materials.

Like many other things, sound can hit and bounce off of other things. In the same way, ocean waves bounce off rocks and crash into shores, sound reacts in the same way. Sound waves have energy, and they transfer this energy into things that they hit. When the sound waves hit the thin bottom of a paper cup, they make it vibrate. This vibration is transferred into the string, and the string travels toward the next cup.

Elena Jones

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