* 1 hard boiled egg (shell removed) * a clear glass bottle whose neck is slightly smaller than the egg * a piece of paper or candle, and a match
Prove the egg will not go into the bottle by itself by placing it on top of the bottle. (If the sizes are right, trying to force the egg in will mangle it horribly!) Take the egg out and crumple up a 3-inch square piece of paper. Light the paper on fire and drop it into the bottle, then quickly place the egg on top. The egg sits a moment; then the flame dies, and the egg slips in!
The burning paper heats the air, making it expand. When the burning stops there is less air inside the bottle than outside, so the greater air pressure outside PUSHES the egg into the bottle.
Can you think about how to get the egg back out of the bottle?!