Discovering Air Pressure: A Science Lesson

Peeled hard boiled egg

Glass milk bottle

Matches

What do the students know about air pressure? What is air pressure? Have students write in their science journals what they think the definition of air pressure is.

Show the egg on top of the opening of the milk bottle. Ask the students what they think will happen if the egg sits there without any interference. Discuss how the egg could be forced to drop into the jar without physically pushing it in. Have the students answer the following question in their science journal: What will happen if a lit match is dropped into the milk bottle and then the egg is placed on top?

Air pressure is a force that constantly surrounds us. At sea level we do not notice the air pushing down and around us from all sides. As we travel below sea level, air pressure increases. This is why divers must use compressed air. The further above sea level we travel air pressure decreases. Climbers to Mt. Everest usually use bottled oxygen to compensate for lack of oxygen and air pressure.

Place egg on top of milk bottle and observe what happens. Remove the egg. Light a match and carefully drop it into the bottle, the match must remain lit until the egg is replaced on top of bottle. When the match flame goes out, the egg should drop effortlessly into the bottle.

What caused the egg to drop into the bottle? Why? Students should be able to conclude that the match consumed oxygen in the bottle thus changing the air pressure. The air pressure outside of the bottle was then greater than the air pressure inside the bottle and the egg was “pushed” into the bottle by air. Did the egg perform as the student first hypothesized in their science journal? If not, what was the expected outcome?

How can you get the egg out of the bottle? Is there a way to use pressure to remove it?

Hint: fill the bottle 2/3 with vinegar and add two tablespoons (more for a large bottle) of baking soda, hold bottle upside down over a tub or sink, this is messy but impressive, as the egg will eject.

Have students write about the experiment in their science journals. Answer the hypothesis based on the experiment.

Use a slightly damp egg; it will slide into the bottle better. Make sure the egg can actually fit through the opening. Small to medium eggs work best, large and jumbo eggs do not always work well. Try to center the lit match when it drops.