For these experiments, you’ll need a glass bottle whose neck is a little smaller than a hard-boiled egg, medium- sized, peeled hard-boiled eggs, a banana, a birthday candle or two, and a long match or grill lighter. I’d recommend using the smallest eggs in the carton (extra-large eggs may not work) for this project. I went out to my recycling bin and discovered that my Trader Joe’s grape juice bottle is the perfect size. This experiment involves flame, so requires adult supervision, and may take a few tries, but it’s really fun when it works. Here’s a link to a demonstration I did (on Kare11 news) of this experiment that will walk you through the steps!
Peel the hard boiled egg, set it on the bottle, and let your children verify that it won’t easily squeeze through. Remove the egg. Cut a thick slice of banana as your “candle holder”, stick the candle in, and drop it into the bottle. Light the candle and set the egg on the bottle, making sure it forms a tight seal.
Now, sit back and watch what happens. Don’t pull the egg off when the candle goes out since it may take a while for the egg to be “pushed” into the bottle by the atmospheric pressure!
What happens? When the candle goes out from lack of oxygen, the remaining air in the bottle cools rapidly, decreasing the air pressure in the bottle and creating a partial vacuum. The outside air, who’s pressure is higher, actually pushes the egg into the bottle as it attempts to equalize the pressure inside of the bottle.
It’s also really fun to do the same thing, upside down, and it’s a little less tricky. Put two birthday candles in the wide end of a hard-boiled egg. Light them and hold them under the inverted bottle to warm the air inside.