1. Water in Earth’s Atmosphere

2. 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.

3. 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.

4. 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.

5. 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.

6. 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?

7. 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://earthguide.ucsd.edu/earthguide/ diagrams/watercycle/ http://ga.water.usgs.gov/edu/watercycl e.html (USGS water cycle in different languages) http://ga.water.usgs.gov/edu/watercycl e.html