1. Weather and Climate
Chapter 2
February, 2011

2. Bell Work What is condensation? What is dew point?
Can you find dew in the air?

3. What is weather? Weather
A condition in the atmosphere at a particular time and place

4. Water in the Air 1. Water in the air effects weather
2. Forms of water in the air
A. Gas
As water vapor
B. Solid
Ice (snowflakes)
C. Liquid
rain

5. Water Cycle
1. Constant movement of water from land to air and back to land again
2. Precipitation-
“Let it Snow” lab

6. “Let it Snow Lab” Follow Directions
Equipment needed is at the lab stations
Lab Safety?

7. “Let it Snow”
Graduated Cylinder

8. “Let it Snow”
Beaker

9. “Let it Snow” Rules 1. No throwing snow 2. No walking in the snow
3. No eating snow……….yuck!!!!!!!!
4. Act like MATURE 7th graders.

10. Water Cycle Review 1. Condensation 2. Evaporation 3. Transpiration
Water vapor cools and changes back into liquid droplets (how clouds form)
2. Evaporation
Liquid water changes into water vapor
3. Transpiration
Plants release water vapor into the air
4. Precipitation
Rain, snow, sleet, or hail falls from the clouds to Earth’s surface

11. Humidity 1. Humidity (pg. 37) in book 2. As water evaporates
Amount of water vapor or moisture in the air
2. As water evaporates
Humidity of the air increases
3. Warmer air holds more water vapor
4. Colder air holds less water vapor

12. Relative Humidity 1. Relative Humidity
Amount of moisture the air holds compared to the maximum amount it can hold at that temperature
Amount of water in the air ÷
Amount of water the air can hold x 100
2. Saturated
When air holds all the water that it can hold at that temperature
Saturated air has a relative humidity of 100%

13. Water Vapor Versus Temperature
1. If the temperature stays the same-
Relative humidity changes as water vapor enters and leaves the air
2. The more water vapor that is in the air
The higher the relative humidity is
3. Relative humidity is affected by changes in the temperature
If water vapor in the air stays the same,
Relative humidity ↓ as temperature ↑
Relative humidity ↑ as temperature ↓

14. Bell Work What is relative humidity?
Does warm air hold (more or less) water vapor than cold air?

15. Measuring Relative Humidity
1. Psychrometer
2. Instrument used to measure relative humidity

16. Measuring Relative Humidity
1. Sling Psychrometer
2. Has 2 thermometers
A. Dry bulb measures temperature

17. Measuring Relative Humidity
E. If there is more humidity in the air, the water in the cloth will evaporate less and there will be little temperature change
Sling Psychrometer
B. Wet bulb is covered with a damp cloth
C. As air passes over the wet-bulb, the water in the cloth begins to evaporate, and the thermometer begins to cool
D. If there is less humidity in the air, the water in the cloth will evaporate more quickly and the temperature will drop

18. Measuring Relative Humidity
Amount of water in the air ÷
Amount of water the air can hold x 100

19. Measuring Relative Humidity
1. Psychrometer
-a. Find the dry bulb
reading
-b. Find the wet bulb
-c. Find the difference
-d. Find RH

20. Bell Work
1. Which

21. Bell Work Fill in the blanks
If the humidity is low, a ______amount of water will evaporate from a wet-bulb thermometer and the _____ between the wet-bulb reading and the dry-bulb reading of the psychrometer will be high.
If the dry bulb reads 10 C, and the difference between the thermometers is 8 C, the relative humidity is_______.

22. Condensation 1. Process when a gas, like water vapor, becomes a liquid
2. Before condensation can occur, the air must be saturated: it must have a relative humidity of ___100%_____
3. Condensation occurs when saturated air cools

23. Dew Point
1. Air can become saturated when water vapor is added to the air……
or when it cools to its dew point
2. Dew Point-
temperature to which air must cool to become saturated
Example……

24. Dew Point 3. Before it can condense,
water vapor must have a surface to condense on

25. Bell Work What is condensation? What is dew point?
Can you find dew in the air?

26. Making Dew
The ice brought the temperature of the can down to dew point and the moisture in the air condensed.
It formed from the water vapor in the air.
The other items in the room were not at dew point
It is the temperature at which dew forms.
Lower

27. Making Dew 6. All the items would be wet.
7. When you take a hot shower or bath, you add moisture to the air and it condense on the cold mirror.
8.At night, these things cool down to the dew point temperature and the water vapor in the condenses on them.
9. No, not all things can cool down to dew point.

28. Making Dew
10. Dew does not fall, it forms
11. It evaporates

29. Making Frost 1. It formed from water vapor in the air 2. Yes
3. The temperature of the can was below freezing point
4. Both are formed from water vapor in the air. They both form on cool surfaces.
5.Dew is a liquid. Frost is a solid.

30. Making Frost
6. No. Frozen dew would look like frozen drops of water. Frost is made of tiny crystals. When dew forms and then freezes, frozen dew is created. Frost is formed when water vapor turns directly into a solid, skipping the liquid phase. (sublimation)
7. Dew is formed when water vapor in the air condenses of surfaces that have cooled down to dew point. Frost is formed at freezing point

31. Making Frost
8. Frost forms on objects at Earth’s surface. Snow forms in the atmosphere and falls to the ground.
9. Snow

32. Clouds
Clouds-
Are a collection of millions of tiny water droplets or ice crystals