dew point

When air is very humid, it doesnt have to cool very much for water vapor in the air to start condensing. The temperature at which condensation occurs is called the dew point. The dew point varies depending on air temperature and moisture content. It is always less than or equal to the actual air temperature, but warmer air and moister air have dew points closer to the actual air temperature. Thats why glasses of cold drinks sweat more on a hot, humid day than they do on a cool, dry day. Q: What happens when air temperature reaches the dew point? A: When air temperature reaches the dew point, water vapor starts condensing. It may form dew (as on the spider web in the opening image), clouds, or fog. Dew forms on solid objects on the ground. Clouds form on tiny particles in the air high above the ground. Fog is a cloud that forms on tiny particles in the air close to the ground.



from gas to liquid

The drops of water on the spider web are dewdrops. They formed overnight when warm moist air came into contact with the cooler spider web. Contact with the cooler web cooled the air. When air cools, it can hold less water vapor, so some of the water vapor in the air changed to liquid water. The process in which water vaporor another gaschanges to a liquid is called condensation. Another common example of condensation is pictured in the Figure 1.1.

condensation and the water cycle

The water cycle continuously recycles Earths water. Condensation plays an important role in this cycle. Find condensation in the water cycle Figure 1.3. It changes water vapor in the atmosphere to liquid water that can fall to Earth again. Without condensation, the water cycle would be interrupted and Earths water could not recycle. Q: In the water cycle, what happens to water after it condenses? A: After water condenses, it may form clouds that produce precipitation such as rain.

instructional diagrams

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the dew point depends on the

a) speed of the wind.

b) temperature of the air.

c) amount of moisture in the air.

-->  d) two of the above

the dew point is always less than or equal to the air temperature.

-->  a. true

b. false

warmer air can hold more water vapor than cooler air.

-->  a. true

b. false

condensation is responsible for forming

a) dew.

b) fog.

c) clouds.

-->  d) all of the above

clouds consist of large masses of water vapor.

a. true

-->  b. false

diagram questions

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