1. EVAPORATION AND HUMIDITY
INV. 6 (PART 2)
EVAPORATION AND HUMIDITY
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2. REVIEW OF PART 1
Explain to your shoulder partner what your group did in part 1 to prove water vapor is in the air.
Share whole class: How do we know that in fact there is water vapor in the air?
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3. Water Vapor
With your shoulder partner, discuss: Do these pictures provide good evidence for water vapor in the air? Could there be another explanation?
Think: How does water vapor get into the air?
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4. EVAPORATION Write the following definition in your notebook.
Evaporation - The PROCESS by which LIQUID WATER becomes a GAS called WATER VAPOR.
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5. Water in the Air?
Dampen a small area on the back of both hands
Fill a cup half full of water
Gently blow on the spot on your left hand to simulate wind.
Tell your shoulder partner why you think your hand feels cold.
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6. Why? Heat is required to evaporate water
Energy transfers from hand to water by conduction.
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Reduced heat = cold signal to your brain

7. QUESTIONS (WIND) Think: What effect does wind have on the wet spot?
Think: Where did the water go that was on your hands?
Discuss with shoulder partner: How is this similar to the weather?
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8. Procedure For each pair: Two thermometers Two pieces of fabric
Two rubber bands
Paper towel
Double tables will share the cup of water
Think and Discuss: How could you use the materials to measure temperature change during evaporation?
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9. Starting temperature
What is the starting temperature of your thermometer?
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10. Procedure (con’t)
Wrap a piece of muslin around the bulb end of your thermometers securing with rubber bands
Dip the muslin end of 1 thermometer into the water blotting excess water
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11. Procedure (con’t)
How can you increase the amount of evaporation from the fabric?
Waving the fabric back and forth rapidly
Wave your wrist back and forth
Take turns
Will shake for 1minutes and then 5 minutes
Record data in a table
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12. TABLE Temp. @ 1 Min. Wet Fabric Dry Fabric Starting temperature
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13. Results Think: What happened to the water on the fabric?
Think: What caused the temperature to go down?
Remember:
Evaporation (liquid to vapor) requires energy
Energy = heat in the environment
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14. Discuss Results
What happened to the water on the fabric when you waved the thermometer around in the air?
Water evaporated
When water evaporates from a surface, what happens to the amount of water vapor in the air?
It increases
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15. DISCUSSION CONT. What is required for evaporation to happen?
Where did the heat come from?
When you take heat energy away from an object, does the object get warmer or colder?
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16. DISCUSSION CONT. So, if evaporation requires heat energy—
Where did the energy come from?
When energy transfers from an object, does the object get warmer or cooler?
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17. Vocabulary Water vapor is the gaseous phase of water
Evaporation is when liquid water changes from a liquid to gas (water vapor)
Humidity is water vapor in the air
When it is humid = there is more water vapor in the air
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18. Saturated When the air contains as much water vapor as it can
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Only a little bit of water vapor to saturate cold air
Takes a lot of water vapor to saturate warm air

19. Relative Humidity
How meteorologist often describe the amount of water vapor in the air
Measured in percentages (%).
Compares the amount of water vapor in the air to the amount needed to saturate the air
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20. Relative Humidity = 100% The air is saturated with water vapor
Air can’t absorb any more water
No evaporation occurs
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21. Into the Air Water vapor gets into the air several ways
Liquid water can evaporate when it absorbs energy (radiation and conduction)
Transpiration : water vapor given off from vegetation
All terrestrial animals breath out vapor
Fires
Volcanic eruptions
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22. Hygrometer Measure relative humidity
Measures the water vapor in the air and compares that to the amount needed to saturate the air
Relative Humidity as a percent
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23. Calculating Relative Humidity
Use lab pages 31/33
Record thorough notes with teacher using examples on lab page 31
Work as tables to complete the rest of the sheet.
Complete side 2 (pg. 33) together.
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Student Lab Notebooks