How Does It Work
The Fizz-Keeper pump is like a miniature bike pump that screws snugly onto the mouth of plastic bottles. It’s designed to keep the fizz in a partially filled bottle of soda pop. The pump forces air into the bottle which is like inflating a bike tire. A marshmallow is basically sugar and gazillions of air bubbles. In fact, marshmallows are about 40-60% 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 about equal and the marshmallow holds its shape.When you increase air pressure inside the bottle, the higher pressure reduces the size of the trapped bubbles. The marshmallows wrinkle and shrink as a result. When you equalize the pressure by loosening the pump, the bubbles expand again and the marshmallows do, too.
You can use this activity to study the effects of atmospheric pressure. People sometimes refer to things being “as light as air,” but the truth is that the air surrounding Earth weighs a lot and exerts considerable pressure on its surface. The atmospheric pressure at sea level is 14.7 pounds per square inch (76 cmHg). That’s roughly two gallons of milk on top of each square inch (6.5 sq cm)! Consider that a typical large marshmallow has a surface area of about 6 square inches (39 sq cm). So, the marshmallow has about 88 pounds of atmospheric pressure (455 cmHg) being exerted upon it (6 square inches x 14.7 pounds per square inch = 88.2 pounds).
