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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
Stupid Egg Tricks.
-Tamara
(published on 10/22/2007)
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