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Clouds form when water vapor in the atmosphere begins to condense. Water droplets and ice form around pieces of dust and other particles in the air. Tint droplets of water and ice crystals in the air form clouds. Air currents keep these droplets of water and ice from falling to earth. Clouds get their name from the way they form.

Light, feathery clouds are made of ice crystals. They form at height above 10,000 meters. These clouds are called cirrus (SIR-us) clouds. When rising currents of warm air form clouds they get big and puffy. A they form, they blossom to great heights. The bottom of these cloud are usually flat. These clouds are called cumulus (KYOOM-yuh-lus) clouds.

Then there is the sheet of clouds that covers most of the sky. These are Stratus (STRAT-us) clouds. They are made layer upon layer and are low clouds. These, however, are not the lowest clouds. Some clouds form on the ground. This kind of cloud is called Fog. At night, the ground cools and causes the air above the ground to cool. Water vapor in the air is pushed out as the air molecules move together more, squeezing out the water. The water falls out of the air forming a cloud we call Fog. If the air near the ground cools fast, condensation will take place. The temperature where water begins to condense out of the air is called the Dew Point. Condensation occurs when we cool off saturated air. When he water falls or condenses out of the air, getting everything wet, we call it Dew.

Warm air, with more space between molecules of air, can hold more water vapor than cold air can. As the air cools off, it can hold less and less water vapor as the molecules of air get closer and closer together. The saturation point of the air changes with temperature. As the spaces between the air molecules changes, so does the saturation point, and Relative Humidity.

In this Investigation [7]...

Students will learn about the different type of clouds that form and the weather associated with those type of clouds. Students will also learn to predict the percentage of cloud cover.

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