• condensation
    From the outside in: condensation, can, cola.

    Photograph by Robert Weber, My Shot

    Making Rain
    Cloud condensation nuclei (CCN) are microscopic bits of clay, salt, or solid pollutants such as ash from smoke. Water in clouds condenses around these condensation nuclei to form raindrops.

    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.

  • Term Part of Speech Definition Encyclopedic Entry
    atmosphere (atm) 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.

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