Concepts:cloud formation

Materials:empty clear soda bottle (with cap), source of smoke particles (a match works well), water

Put some water in your bottle. Light your match, blow it out and drop it into the bottle. Tightly place your cap on the bottle. Give the bottle a squeeze then release the squeeze. Upon releasing the squeeze you should see some fog develop in the bottle! On occasion, it takes a few tries to get it going. Squeezing the bottle again makes the fog instantly go away.

Why does it work? Squeezing the bottle makes the bottle (slightly) smaller, thus forcing the air particles to get closer together and thus increases (slightly) the air pressure and temperature in the bottle. When you release the bottle the air expands back into its original volume lowering the pressure and temperature in the bottle to the point where the moisture in the air can condense. It will not work without the smoke particles. Why? Water (even in the air) always has to have something to condense on.

So, squeeze and release to your heart's content!

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