|MadSci Network: Earth Sciences|
Condensation forms when water molecules in relatively warm air come into contact with a cold surface. As the molecules cool down, they begin to move about more slowly and draw closer together. If they are cooled down enough, they begin to stick together -- they no longer have the energy to overcome their natural attraction for one another. (It sounds like a soap opera plot, doesn't it?) As more and more molecules stick together, visible droplets of liquid water form on the surface. This, incidentally, is the same process that creates rain. The "cold surface" is a mass of cooler air in the atmosphere. Water starts to condense on the surface of tiny dust particles in the air, and form raindrops.
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