The Water Cycle

When water is heated, it changes from a liquid to a gas. This gas is called water vapor, and the process is called evaporation. When plants give off water vapor, it's called transpiration.   When water evaporates, it rises into the cooler air, collects, and forms clouds.  There, the water vapor molecules cool down and change back into liquid water.  This is called condensation.    

As more and more water vapor cools into the clouds, the water droplets that form the clouds become larger and larger. These droplets get so big that the swirling winds in the atmosphere can no longer hold them up. The droplets fall from the sky. 

Precipitation is the term for the falling, condensed water molecules, which come down as rain, snow, sleet, or hail--depending on conditions in the atmosphere.
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When water falls to the Earth, the water seeps into the soil because of the force of gravity. This seeping is called infiltration. Or the water flows over the land and into bodies of water, such as rivers and lakes. Most of this precipitation falls in either coastal areas or in elevations high up in the mountains.  Some of the water that falls in high elevations becomes run-off water, which is water that runs over the ground to lower elevations and forms rivers, lakes, and valleys. Sometimes this water collects nutrients from the soil it runs over, making the valley good for plant growth.

Review: The water cycle is a process that is constantly recycling the Earth's supply of water.  This is important because humans, animals, and plants all need water to survive. To review, let's go through the water cycle step by step:
a. First the water from the Earth's surface evaporates. Then it rises into the atmosphere, is cooled, condenses, and forms clouds.
b. When enough water collects in the clouds, they release moisture in the form of rain, sleet, snow, or hail. And once again, the water returns to the Earth.
c. The water that's fallen to the Earth runs off into lakes, rivers, streams, and any other body of water. This water will eventually seep through layers of the Earth's surface where impurities filter out.
d. Then, the water is heated by the sun and evaporates, and the whole cycle begins again.

Now that you've learned about the water cycle, discover how to make your own miniature water cycle at home. Then you can use this mini water cycle to conduct your own investigations!