Transcript Weather Lesson 2 - Jamestown Public Schools

Chapter 8 Lesson 2
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Water Vapor
• The water in the air is water vapor.
• Water Vapor is invisible, odorless,
colorless, and tasteless.
• The amount of water vapor in the air is
called humidity.
• Water on the covering the Earth - oceans,
lakes, and rivers changes into water
vapor through the process of
evaporation.
Condensation
• Condensation is the changing of a gas
into a liquid.
• When air is cooled the molecules show
down and the water vapor molecules
collide and stick together changing into
liquid droplets on cool surfaces.
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QuickTime™ and a
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Relative Humidity
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• Relative Humidity is a comparison
between how much water vapor is in the
air and how much the air could hold - at a
given temperature - if it were full or
saturated.
• Relative humidity is given in percents.
• 50% relative humidity means that air is
holding half of what it could if it were full.
• The higher the relative humidity, the less
water can evaporate into the air. The less
water, such as sweat, can evaporate from
our skin, the wetter and stickier the air
feels.
Clouds
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• Warm air holds more moisture than cold
air.
• Warm air is lighter than cold air, so warm
air rises.
• As warm air rises it cools and the water
vapor condenses.
Warm Moist Air Cools
• Air can cool by being pushed upward over
mountains by winds.
• Cool air can be heated by the ground as the
sun warms the ground. It then becomes warm
air and rises. As it rises, it expands and cools.
• Air can also be pushed upward when cold and
warm air meet. The lighter, warm air is pushed
up over the heavier, cold air. The warmer air is
pushed up and cools.