Clouds in a Bottle
Clouds are created when water vapor and air pools and condenses, or changes from a gas to a liquid. As it moves upward, the air cools until it reaches the dewpoint, the point at which it is saturated with water vapor. The shapes of the clouds that form depend on the stability of the surrounding air.
Open a can of carbonated soft drink, being careful not to shake it up. Watch carefully to spot the fog that comes from the opening. The pressure on the gas inside causes the internal temperature to rise. When the pressure is released, the gas cools. When the can is opened, pressure inside the can is released, and you see the water vapor condense as the gas (air, carbon dioxide, and water vapor) cools. There are other ways to see a process similar to cloud formation. Watch dry ice (frozen carbon dioxide), or watch the clouds that are released when you open the door of the ice section of a refrigerator.
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Updated: January 22, 2003