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Water in Earth’s Atmosphere. Phase changes. To evaporate, water must absorb energy. This energy goes into changing the liquid particles that are close together to a gas where particles are far apart and moving fast. Water vapor carries this energy into the atmosphere with it. Phase changes.
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Phase changes • To evaporate, water must absorb energy. This energy goes into changing the liquid particles that are close together to a gas where particles are far apart and moving fast. • Water vapor carries this energy into the atmosphere with it.
Phase changes • When water condenses it releases this energy into the atmosphere to be used by other particles which can use it to increase their speed and pressure.
Relative Humidity • At any given time, there is a certain amount of water vapor in the air. • Air can hold more water when it is hot and less when it is cool. • Relative humidity measures how much water vapor is in the air compared to how much water vapor the air can hold at the given temperature.
Relative Humidity • Relative humidity is determined by using a sling psychrometer. One of the thermometers has a wick covering the bulb which is wet. When this is swung, the water evaporates and the wet thermometer’s reading drops.
Relative Humidity • Comparing the two temperatures tells how much water is present in the air compared to the maximum possible. • If the readings are far apart, what does that indicate about the RH?
The Water Cycle • Energy and water are constantly moving to and from the atmosphere through the water cycle. • http://earthguide.ucsd.edu/earthguide/diagrams/watercycle/ (animation) • http://ga.water.usgs.gov/edu/watercycle.html (USGS water cycle in different languages)