Pumping the Fizz-Keeper forces molecules of air into bottles, just like inflating a tire. While marshmallows are present in the bottle, this increased air pressure makes the marshmallows shriveled, wrinkly, and shrink. Why? Well, it’s because marshmallows are just sugar and air. In fact, marshmallows are comprised of about 40-60% air. When you increase the air pressure inside of the bottle beyond the regular pressure outside, the force actually crushes the marshmallow’s air pockets.
You can 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 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 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.