We'll do still another trick with air pressure, and maybe, someday, we'll find out what purpose this kind of a trick serves. [We have seen that all the fun stuff we've done so far has a real purpose.]

Invert a bottle or jar over a burning candle that is set in a tray of water. The candle will heat the air inside the container.

As the air is heated, bubbles will be driven from the mouth of the container. (The air inside expands, and the increased pressure forces out some of the air that was inside.)

This writer, not being a brilliant scientist, but having paid attention in earlier activities, remembers that we can't have fire without air. It seems, then, that the candle will stop burning when it runs out of air inside the container.

When the candle is extinguished and the air inside cools, water will enter the inverted container.

You will realize that this is caused by a reduction in air pressure inside the container. (The outside air pressure is greater than that inside the cooled jar, and its push on the surface of the water forced some of it into the container.)

We'll have to find out how this can help us in the "real" world.