Learn something about how gases react when they are heated - extra points to anyone who can work out how to get the egg out (intact)!
- An egg (hard-boiled)
- A bottle (neck only a little bit smaller than egg)
- Newspaper or tea-lights
Firstly, make sure your egg is hard-boiled as doing this with a raw egg will be really messy. If you're doing this at a school, how about soaking the eggs in food dye for a few minutes then having a race to see who's egg makes it into the bottle the quickest? Nb. Freshly cooked eggs are needed - they go a bit rubbery and shrink if you leave them overnight.
Peel your egg (easier if you've let it cool down first)
Put a few bits of screwed up paper into the bottle and light. I've found that tea-lights (mini-candles) are pretty good for this too - the paper can burn a bit fast. You'll need a long splint to light the candle.
As soon as its burning, place egg on top of bottle and watch the magic.
Why does this work?
Some sites will tell you that the reason for the egg ending up in the bottle is that the egg seals the bottle and the burning paper then uses up all the oxygen in the bottle and this causes a pressure difference that sucks the egg in. Sorry to disappoint you, but this is completely wrong!
Lets think about it, when something burns, it does use up oxygen but it also produces carbon dioxide so the actual volume of gas does not change. What is actually happening is the air inside the bottle is heated by the fire and, as we all know, when you heat a gas it expands. This means that some of the air is pushed out of the bottle as it can no longer fit inside. Then you go and put the egg on the bottle and this seals it. The fire then has a problem because the egg has cut off its supply to oxygen and a fire needs oxygen to burn. This is why the fire goes out when you put the egg on top. When the air inside the bottle cools down, it shrinks back to its normal volume but, due to the egg sealing the top, all the air that was originally pushed out can't get back in. This is what causes the difference in pressure that results in the outside air pressure pushing the egg into the bottle.
To get the egg back out you can either turn the bottle upside down so the egg seals it from inside and heat the bottle, or you can blow into the bottle really hard and then quickly turn it over to seal the neck (good luck).