1. Using the Symbol Key from the next slide…fill in this chart at your seat.

3. Humidity “An excuse for the 80s”

4. What is Humidity?
Humidity refers to the amount of moisture (water vapor) in the surrounding air.

5. Relative Humidity
RATIO of the amount of moisture in the air compared with the amount of moisture the air can hold at that temperature and pressure.
Expressed as a percentage.

6. I would rather be in the desert than in North Carolina during July!!!
If the air is at 90% relative humidity, sweat will not evaporate into the air.
As a result, we feel much hotter than the actual temperature.
If the relative humidity is low, we can feel much cooler than the actual temperature.
because our sweat evaporates easily, cooling the body.

7. We are very sensitive to humidity
We are very sensitive to humidity. Sweating keeps our body cool and maintain its current temperature.

8. AGHHH my hair is HUGE, WHY?
The length of a strand of human hair changes with different relative humidities.
As the relative humidity increases, hair becomes longer, and as the humidity drops it becomes shorter. On very humid days, your hair actually becomes longer and this extra length causes the frizziness that gives us bad hair days.

9. How is Relative Humidity Measured?
Sling Psychrometer
It consists of two identical mercury thermometers:
Evaporating water from the wick absorbs heat from the thermometer bulb, causing the thermometer reading to drop.

10. Find the difference between the DRY bulb and the WET bulb on the two thermometers
Use the Relative Humidity Table
Where the DRY bulb temperature and the DIFFERENCE between the two thermometers intersects…is your relative humidity.
Example – If the DRY bulb temperature reading is 22°C and the DIFFERENCE between the two thermometers is 6°…the relative humidity is 53%

11. Practice Problems Dry bulb = 12° Wet bulb = 7° 48% 2. Dry bulb = 22°
83%
3. Dry bulb = -10°
Wet bulb = -7° 0%

12. Why Care about Relative Humidity?
If we can’t sweat…we could overheat and DIE!!

13. Dew Point
The temperature that air would need to cool to condense the water vapor into liquid water.

15. Dew Point is determined the SAME EXACT WAY that Relative Humidity is calculated…a Sling Psychrometer.
You just use a DIFFERENT chart… the DEWPOINT chart..DUH!!
Dry bulb = 12°
Wet bulb = 7° 1°
2. Dry bulb = 22°
Wet bulb = 19°
17°