Marshmallow Masher

Safety Notes: This demonstration requires adult supervision! Use only plastic soda bottles that are in good condition for this experiment. Wear safety glasses just in case something breaks. Don’t get carried away with the pumping. Do not over-pressurize any container using the pressurizing pump. Too much pressure will result in the breakage of the pump. Do not pump more than 40 strokes (pumps) into the 16 oz bottle. Apply only enough pressure to allow you to see the shrinking effects. Never leave a soda bottle in the pressurized state. After observing the effects of compression, always release the pressure.

1. Fill the bottle about half full with marshmallows and screw on the special pressurizing pump.
2. Begin pumping to increase the pressure within the bottle. As you increase the pressure inside the bottle, notice how the marshmallows seem to become wrinkled and shrink. Do not pump more than 40 times!
3. Release the pressure by unscrewing the cap, but don't take your eyes off the marshmallows. Let's just say the rapid decompression is well worth all of the effort of pumping!

How does it work?

The Fizz Keeper is like a miniature bicycle pump that forces molecules of air into the bottle. The increased pressure, in turn, pushes on the marshmallows. Since marshmallows are just puffy pockets of air, the increased pressure compacts the molecules and the marshmallows shrivel up.

Teacher Notes: Use this demonstration to discuss the effects of atmospheric pressure. We sometimes refer to things as being “light as air,” but the truth is that the air surrounding our planet weighs a lot and exerts considerable pressure on us. The atmospheric pressure at sea level is 14.7 pounds per square inch of surface area. That’s roughly the weight of 2 gallons of milk resting on 1 square inch!

A typical regular-sized marshmallow has a surface area of about 6 square inches. So, the marshmallow has about 88 pounds of atmospheric pressure being exerted upon it (6 square inches x 14.7 pounds per square inch = 88.2 pounds). The marshmallow is really a kind of sugary material that resembles foam rubber. It’s full of tiny bubbles of air. The air pressure inside these tiny bubbles is roughly the same as the air pressure pushing on the marshmallow from the outside, so the pressures are equalized and the marshmallow retains its regular shape.

Additional Info

What would happen if you pulled all of the air out of the bottle instead of pumping extra molecules into the bottle? Take a look at the Incredible Growing Marshmallow Trick.