This month we’ll be dealing with “pressure” to make a science experiment/magic trick with cups “magically” sticking to a balloon. Are you ready to amaze? 

Materials: 

A large balloon to be blown up.

Two plastic cups (paper cups work well, too, but don’t use glass as you might drop them).

Procedure:

Start to blow up a balloon (you may need someone else’s help to do the next couple of steps).

After filling the balloon partially, hold two cups onto the sides of the balloon. Push them tightly against the balloon!

Continue to blow up the balloon and then let go of the two cups.

Be amazed as the two cups stick to the side of the balloon.

Explanation:

Physics is a branch of science that deals with forces, motion and energy. A force is a push or a pull, caused by people or other things like magnets or gravity. This experiment deals with a force called “pressure” which gives us a thing called a “vacuum.” A vacuum is formed when there is a low amount of pressure, which is determined by the amount of air in an area. If you push the air out of something it forms a vacuum, which other things try to fill up. When you keep the cups against the side of the balloon and continue to blow it up, the balloon pushes into the cups and forces air out and thus creates a vacuum. The air outside of the cup wants to fill this vacuum and since there is a nice seal around the edge of the cup (like a plunger on a smooth surface) it keeps the balloon tightly stuck together.     

Experiment further: 

Can you think of anything else you can experiment with in this lab? Different sized balloons? Other types of cups or bowls? What if you made the cups have a wet surface to them as you stick them to the balloon? 

I hope you enjoyed this simple experiment. If you have more questions about this, specifically around the science fair aspect of this experiment, contact the author. 

Steve Davala is a high school chemistry and physics teacher who likes to write and work with Photoshop. He’s got two kids of his own and subjects them to these science activities as guinea pigs.