Concepts: convection & air pressure
Materials: paper, matches, glass bottle (these are getting
very hard to find these days!), at least
one hard boiled egg (pealed). Optional Materials:
liquid nitrogen
A small amount of burning paper is placed into the glass bottle. The egg is placed at the mouth ofthe bottle ("pointy" end down), the flame goes out and it is "sucked" into the bottle.
Be advised that the incorrect explanation is often given for this one. Most people claim that thefire "uses up the oxygen." Nothing could be further from the truth! What really happens is that the fire heats the air in the bottle, which in turn causes it to expand and rise. (With a good fire the egg will actually bob up and down on the mouth of the bottle as escaping air rushes past it.) The fire eventually extinguishes itself, the air in the bottle (no longer heated) contracts thus lowering the air pressure in the bottle (Remember, some of the air left the bottle so there is less air and air pressure in the bottle). The greater pressure on the outside of the bottle is greater than the pressure in the bottle so the egg gets pushed in! Plop!
To remove the egg: Invert the bottle to allow the egg to roll back to the bottle neck then blow into the bottle. Air will go in around the egg and into the bottle - thus raising the pressure within the bottle. When the pressure in the bottle exceeds room air pressure the egg will be pushed backout.
The egg can also be "sucked" into the bottle with no fire at all.
If the egg is placed on the bottle and then the air within the bottle
is dramatically cooled - the air will contract and lower the
pressure within the bottle. This dramatic cooling can be done by
placing the bottle into an inch or so of liquid nitrogen. After the
egg plops into the bottle additional air from the room will fall into
the bottle, cool and contract. After a few minutes you can take the
bottle away from the liquid nitrogen and then quickly invert the
bottle so that the egg blocks the mouth of the bottle. As the air
within the bottle warms up it will expand and push the egg out of the
bottle! This helps to show that the fire from above
does not use up the oxygen!
Be advised that repeated attempts will eventally cause the bottle to break from the temperature induced stress.
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