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Q & A: Egg in a Bottle

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Most recent answer: 10/22/2007
Q:
We have a disagreement in our home school. The "egg in the bottle" experiment is the source of discussion. The book says that the egg is sucked into the bottle because oxygen is consumed by the fire. That creates the vacuum. However, could it be that the heat generated by the fire expands the air? When the egg is placed on the bottle, the fire goes out, the air cools becoming more dense creating the vacuum and drawing the egg into the bottle. Please settle this confusion.
- Don Orr (age 43)
SBC Christian Academy, Savoy, IL USA
A:
Don -

Your answer is much more correct than the book's. When the egg is on top of the bottle, the fire does consume the oxygen - this is what makes the flame go out. However, this does not create a vaccuum for two reasons. The first is that most of air is not oxygen; it's nitrogen. Second, when the fire consumes the oxygen, it produces carbon dioxide. And it produces exactly as much carbon dioxide as there was originally oxygen. So this is not enough on its own to lower the pressure in the bottle. After the flame goes out, the air inside cools, exactly like you said. As the air inside cools, the pressure decreases so that the pressure outside the bottle is larger than the pressure inside. This pushes the egg into the bottle.

For more information on the egg in the bottle experiment (and other neat things you can do with eggs), including a cool trick for how to get the egg back out of the bottle again, check out this link to .

-Tamara

(published on 10/22/2007)

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