Encyclopedic Entry

From the outside in: condensation, can, cola.

Photograph by Robert Weber, My Shot

Condensation is the process where water vapor becomes liquid. It is the reverse of evaporation, where liquid water becomes a vapor.

Condensation happens one of two ways: Either the air is cooled to its dew point or it becomes so saturated with water vapor that it cannot hold any more water.

Dew Point

Dew point is the temperature at which condensation happens. (Dew is simply condensed water in the atmosphere.) Air temperatures can reach or fall below the dew point naturally, as they often do at night. Thats why lawns, cars, and houses are often coated with water droplets in the morning.

Condensation can also produce water droplets on the outside of soda cans or glasses of cold water. When warm air hits the cold surface, it reaches its dew point and condenses. This leaves droplets of water on the glass or can.

When a pocket of air becomes full of water vapor, clouds form. The point at which condensation starts can be easily viewed in cumulus clouds, which have flat bottoms. Those flat bottoms are where vapor begins to condense into water droplets.

Saturation

Clouds are simply masses of water droplets in the atmosphere. Molecules in water vapor are far apart from one another. As more water vapor collects in clouds, they can become saturated with water vapor. Saturated clouds cannot hold any more water vapor. When clouds are saturated with water vapor, the density, or closeness, of the molecules increases. The vapor condenses and becomes rain.

Cold air holds less water vapor than warm air. This is why warm climates are often more humid than cold ones: Water vapor remains in the air instead of condensing into rain. Cold climates are more likely to have rain, because water vapor condenses more easily there.

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

atmosphere

Noun

(atm) unit of measurement equal to air pressure at sea level, about 14.7 pounds per square inch. Also called standard atmospheric pressure.

clay

Noun

type of sedimentary rock that is able to be shaped when wet.

cloud

Noun

visible mass of tiny water droplets or ice crystals in Earth's atmosphere.

Encyclopedic Entry: cloud

cloud condensation nuclei (CCN)

Plural Noun

microscopic bits of clay, salt, or solid pollutant around which water vapor condenses in clouds to form raindrops.

condensation

Noun

process by which water vapor becomes liquid.

Encyclopedic Entry: condensation

cumulus

Noun

type of large cloud with a flat bottom and fluffy tops.

density

Noun

number of things of one kind in a given area.

Encyclopedic Entry: density

dew point

Noun

temperature at which water in the air condenses to form water droplets on objects near the ground.

evaporation

Noun

process by which liquid water becomes water vapor.

Encyclopedic Entry: evaporation

humid

Adjective

containing a large amount of water vapor.

lab

Noun

(laboratory) place where scientific experiments are performed.

liquid

Noun

state of matter with no fixed shape and molecules that remain loosely bound with each other.

microscopic

Adjective

very small.

molecule

Noun

smallest physical unit of a substance, consisting of two or more atoms linked together.

pollutant

Noun

chemical or other substance that harms a natural resource.

process

Noun

natural or human actions that create and change the Earths features.

raindrop

Noun

drop of liquid from the atmosphere.

salt

Noun

mineral often used as a preservative or flavoring.

saturate

Verb

to fill one substance with as much of another substance as it can take.

solid

Noun

state of matter with a fixed shape and molecules that vibrate but do not move.

vapor

Noun

visible liquid suspended in the air, such as fog.

Credits

Media Credits

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Writer

Kim Rutledge
Melissa McDaniel
Diane Boudreau
Tara Ramroop
Santani Teng
Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt

Illustrator

Tim Gunther
Mary Crooks, National Geographic Society

Editor

Kara West
Jeannie Evers

Educator Reviewer

Nancy Wynne

Producer

Caryl-Sue, National Geographic Society

Sources

Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

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