EVAPORATION AND HUMIDITY INV. 6 (PART 2) EVAPORATION AND HUMIDITY TG-P.194-195

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? TG-P.196

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? TG-P.196

EVAPORATION Write the following definition in your notebook. Evaporation - The PROCESS by which LIQUID WATER becomes a GAS called WATER VAPOR. TG-P.196

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. TG-P.196

Why? Heat is required to evaporate water Energy transfers from hand to water by conduction. TG-P.196 Reduced heat = cold signal to your brain

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? TG-P.196

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? TG-P.196-197

Starting temperature What is the starting temperature of your thermometer? TG-P.197

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 TG-P.197

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 TG-P.197

TABLE Temp. @ 1 Min. Wet Fabric Dry Fabric Starting temperature TG-P.197

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 TG-P.198

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 TG-P.198

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? TG-P.198

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? TG-P.198

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 TG-P.198

Saturated When the air contains as much water vapor as it can TG-P.198 Only a little bit of water vapor to saturate cold air Takes a lot of water vapor to saturate warm air

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 TG-P.198

Relative Humidity = 100% The air is saturated with water vapor Air can’t absorb any more water No evaporation occurs TG-P.198

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 TG-P.199

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 TG-P.199

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. TG-P.199 Student Lab Notebooks