NASA - National Aeronautics and Space Administration

Evaporation happens when a liquid or a solid changes into a gas. For example, if you put some water into an open pan and leave it in a warm room, the water will slowly disappear. The pan will then be dry and empty because the water evaporated. When water evaporates, it turns into a gas, called vapor. It can take several days for water to disappear this way.

Image to left: Water evaporates slowly as it turns into a gas and mixes with the air. Water evaporates quickly when it is heated. As the water boils, it turns into steam. Credit: World Book illustration by Mark Swindle

An increase in heat makes things evaporate faster. For example, if a person put the pan of water on the stove and then turned on the heat, the water would soon begin to boil. The person might see steam rise off he top of the water. Steam is water turning into vapor.

Evaporation is important to life on Earth. The heat of the sun evaporates water from earth's surface. The evaporated water goes high into the air. Then it cools down, forms clouds, and falls from the sky as rain or snow.

Evaporation is important for people too. When we sweat, water on our skin evaporates. The evaporation makes the skin feel cooler.

A solid may change into a liquid -- for example, when ice melts and becomes water. When a solid, such as dry ice, changes into a gas without being a liquid first, that is called sublimation.

How to cite this article: To cite this article, World Book recommends the following format: "Evaporation." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.

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