What is evaporation

Sublimation is a common way for snow to disappear quickly in arid climates. Source: Mount Washington Observatory. Heat energy is necessary for evaporation to occur. Net evaporation occurs when the rate of evaporation exceeds the rate of condensation.

A state of saturation exists when these two process rates are equal, at which point the relative humidity of the air is percent.

Condensation , the opposite of evaporation, occurs when saturated air is cooled below the dew point the temperature to which air must be cooled at a constant pressure for it to become fully saturated with water , such as on the outside of a glass of ice water.

In fact, the process of evaporation removes heat from the environment, which is why water evaporating from your skin cools you. Evaporation from the oceans is the primary mechanism supporting the surface-to-atmosphere portion of the water cycle. After all, the large surface area of the oceans over 70 percent of the Earth's surface is covered by the oceans provides the opportunity for large-scale evaporation to occur. On a global scale, the amount of water evaporating is about the same as the amount of water delivered to the Earth as precipitation.

This does vary geographically, though. Evaporation is more prevalent over the oceans than precipitation, while over the land, precipitation routinely exceeds evaporation. Most of the water that evaporates from the oceans falls back into the oceans as precipitation. Only about 10 percent of the water evaporated from the oceans is transported over land and falls as precipitation.

Once evaporated, a water molecule spends about 10 days in the air. The process of evaporation is so great that without precipitation runoff , and groundwater discharge from aquifers , oceans would become nearly empty. If you ever find yourself stranded on an island in need of some salt, just grab a bowl, add some seawater, and wait for the sun to evaporate the water. In fact,one way to produce table salt is to evaporate saline water in evaporation ponds, a technique used by people for thousands of years.

Seawater contains other valuable minerals that are easily obtained by evaporation. The Dead Sea is located in the Middle East within a closed watershed and without any means of outflow, which is abnormal for most lakes. The primary mechanism for water to leave the lake is by evaporation, which can be quite high in a desert—upwards of 1, - 1, millimeters per year.

The result is that the waters of the Dead Sea have the highest salinity and density which is why you float "higher " ; when you lay in saline water of any sea in the world, too high to support life. The water is ideal for locating evaporation ponds for the extraction of not only table salt, but also magnesium, potash, and bromine. We said earlier that heat is removed from the environment during evaporation, leading to a net cooling; notice how cold your arm gets when a physician rubs it with alcohol before pulling out a syringe with that scary-looking needle attached.

In climates where the humidity is low and the temperatures are hot, an evaporator cooler, such as a "swamp cooler" can lower the air temperature by 20 degrees F. As this map shows, evaporative coolers work best in the dry areas of the United States red areas marked A and can work somewhat in the blue areas marked B. In the humid eastern U. Here is Fido, looking both sharp and cool as he sports the latest in fashionable dog apparel that also keeps him cool on a hot day.

Fido is wearing a "cooling vest", where the owner wets it down, places it on the dog, and the properties of the evaporation process help the dog stay comfortable. Yes, swamp coolers aren't just for homes anymore. After all, the evaporative process is just as happy keeping a dog cool as it is keeping a house cool. Evaporative coolers are really quite simple devices, at least compared to air conditioners.

Swamp coolers pull in the dry, hot outdoor air and pass it through an evaporative pad that is kept wet by a supply of water. In a home device, a fan draws the air through the pad, the water in the pad evaporates, resulting in cooler air which is pumped through the house.

Much less energy is used as compared to an air conditioner. Source: California Energy Commission. Earth's water is always in movement, and the natural water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth. Water is always changing states between liquid, vapor, and ice, with these processes happening in the blink of an eye and over millions of years.

The air is full of water, even if you can't see it. Higher in the sky where it is colder than at the land surface, invisible water vapor condenses into tiny liquid water droplets—clouds. When the cloud droplets combine to form heavier cloud drops which can no longer "float" in the surrounding air, it can start to rain, snow, and hail What is streamflow? How do streams get their water? To learn about streamflow and its role in the water cycle, continue reading. Perhaps you've never seen snow.

Or, perhaps you built a snowman this very afternoon and perhaps you saw your snowman begin to melt. Regardless of your experience with snow and associated snowmelt, runoff from snowmelt is a major component of the global movement of water, possibly even if you live where it never snows. The atmosphere is the superhighway in the sky that moves water everywhere over the Earth.

Water at the Earth's surface evaporates into water vapor which rises up into the sky to become part of a cloud which will float off with the winds, eventually releasing water back to Earth as precipitation. The air is full of water, as water vapor, even if you can't see it. Condensation is the process of water vapor turning back into liquid water, with the best example being those big, fluffy clouds floating over your head.

And when the water droplets in clouds combine, they become heavy enough to form raindrops to rain down onto your head. You can't see it, but a large portion of the world's freshwater lies underground. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format.

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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. The movement of water throughout Earth can be understood as a cycle where H20 moves from one state of matter to another. Use these standards-aligned resources to teach middle schoolers more about condensation, precipitation, and weather patterns that are affected by, and a part of, the water cycle. The water cycle describes how water is exchanged cycled through Earth's land, ocean, and atmosphere.

The water cycle is the endless process that connects all of the water on Earth. Join our community of educators and receive the latest information on National Geographic's resources for you and your students.

Skip to content. Image Evaporation on a Farm Water evaporates from a sugar beet field after a summer shower in Borger, Netherlands. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

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