Teaching Point: “To compare and contrast relative humidity and dew point.” Do Now Discussion: Which phase change do you think is happening when dew forms on blades of grass? How about when it disappears? How do you know?

Relative Humidity- the percentage of water vapor (humidity) in the air relative to how much the air can hold.  Controlled by air temperature TP: “To compare and contrast relative humidity and dew point.” Humidity Relative to Temperature High temperature = high water capacity = lower R. H Low temperature = low water capacity = higher R.H

A sling Psychrometer has two thermometers (or bulbs), with one bulb covered in a damp cloth. As the psychrometer is slung around, the web bulb cools down while the ‘dry’ bulb stays constant. 1. Step 1: Take the difference between the dry bulb (actual air temperature) and the wet bulb 2. Step 2: Take note of what the dry-bulb temperature is 3. Step 3: Use page 12 of the ESRT to intersect on the correct % relative humidity Calculating Relative Humidity TP: “To compare and contrast relative humidity and dew point.”

ESRT Page 12- Relative Humidity TP: “To compare and contrast relative humidity and dew point.”

A sling Psychrometer can also be used to find the dew point temperature, or temperature at which air becomes saturation with water vapor and condensation begins. 1. Same step #1 as relative humidity. 2. Same step #2 as relative humidity. 3. Use page 12 of the ESRT to intersect on the correct dew point Calculating Dew Point TP: “To compare and contrast relative humidity and dew point.”

Calculating Dew Point TP: “To compare and contrast relative humidity and dew point.”

When air temperature = dew point, R.H. = 100% When the air temperature and dew point values are farther apart, the R.H is decreasing and air is drier. TP: “To compare and contrast relative humidity and dew point.” R.H. and Dew Point Relationships

Quick Assessments Take out your SMART clickers, and wait for me to “start” your class Then, sign into my class and wait for the assessment to start As soon as the assessment starts, you have one (1) minute to answer the multiple choice question TP: “To analyze the water in Earth’s atmosphere.”

Quick Assessments 1.During which time of day is the relative humidity the lowest? a. morning b. mid-afternoon c. evening d. late evening TP: “To analyze the water in Earth’s atmosphere.”

Quick Assessments 2.What is the dew point when the dry-bulb is 14  C and the wet bulb is 8  C? a. 1  C b. –9  C c. 6  C d. 22  C TP: “To analyze the water in Earth’s atmosphere.”

Intellectual Engagement Upon walking to your car in the morning you notice there is a thin layer of ice surrounding the car and on all the glass windows. What can you infer about last night’s temperature, moisture, relative humidity, and dew point conditions? TP: “To compare and contrast relative humidity and dew point.”

Class Activity- R.H. and Dew Pt. Instructions: Using the information we just learned about relative humidity and dew point… Task A- Complete questions 1 through 10 on the handout in front of you Task B- Complete questions 1 through 13 on the handout in front of you Task C- Complete questions 1 through 15 on the handout in front of you Flexible Group- take out your portfolios and meet me at my desk for a conference.

Lesson Summary In your tables of four, go back into your notes and consider what we have just learned today, and then… 1. Identify three (3) important concepts we learned today 2. Place those the three in order from the most important concept to least important. TP: “To compare and contrast relative humidity and dew point.”