1. Chapter 12 Section 4 What is the dew point?
Objective:
Explain what happens when air temperature goes above or below the dew point.

2. Key Terms condensation: changing of a gas to a liquid
dew point: temperature to which air must be cooled to reach saturation
frost: ice formed from condensation below the freezing point of water

3. Condensation Air always contains some water vapor
As the temperature of air drops, water vapor in the air changes form a gas to a liquid.

4. Dew Point Condensation takes place when saturated air is cooled.
If saturated air continues to be cooled, some of the water vapor in the air condenses.
The water vapor changes to a liquid water

5. Dew Point At night, the ground cools faster than the air.
Air near the ground is then cooled by the ground.
The temperature of the air may drop to or below its dew point - condensation takes place.
Drops of water called dew begin to form on grass and bushes and may also form on the windows of cars.

6. DEFINE:
What is dew?

7. Frost The freezing point of water is 0℃.
Water changes from a liquid to a solid.
When the humidity is low, the dew point of the air may be lower than the freezing point of water.
If the air temperature drops below the dew point, water vapor will come out of the air.
However, the water vapor will change directly to ice instead of water.

8. 2. HYPOTHESIZE?
Why doesn’t frost form at temperatures above 0℃?

9. 12-4 Classwork What is the process of condensation?
When does the process of condensation take place?
What is the dew point?
What happens to the relative humidity when the air becomes saturated?
What is the freezing point of water in the Celsius temperature scale?

10. 12-4 Classwork
6. APPLY: Suppose condensation begins to form on the window of a car at 8℃. What is the dew point?
7. CONTRAST: How do evaporation and condensation differ?