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Clouds of water droplets form when warm, moist air is lifted and cooled. This can occur when when warm air rises over mountains or when a mass of heavy, cool air lifts the warm, light air.

Topics and Connections:

• Clouds

Materials:

• hot water
• ice cubes
• large, clear wide-mouth jar
• plastic wrap
• large rubber band
• 2 blackboard erasers

Directions:

Students:

• Cut a piece of plastic wrap large enough to fit over the mouth of the jar.
• Fill the jar about one third full of very hot—not boiling—water.
• Punch a hole close to one end of this strip, and cut the other end to form a point.
• Clap the erasers together in the mouth of the jar so chalk dust goes inside. The dust will give the water vapor places to accumulate 'seeds' around which drops will grow.
• Quickly put the plastic wrap over the jar's mouth with the rubber band and place several ice cubes on top.

Questions To Ask:

• What are the clouds made of?
• Where else have you seen clouds form? (Any time warm air cools, such as when people breathe on a cold day.)
• What takes the place of the chalk dust in a real cloud?
• Why do clouds usually form high up in the sky? (It's cold up there.)

Follow Up:

• Can you make a cloud without dust?
• Can you actually make it rain inside the jar?

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