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Relative Humidity. Is how much moisture a given mass of air is holding compared to how much water that air is capable of holding expressed as a percent. What % full? What would happen to that % if the same water were in a smaller glass?. How to measure humidity -. Sling Psychrometer.
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Relative Humidity Is how much moisture a given mass of air is holding compared to how much water that air is capable of holding expressed as a percent. What % full? What would happen to that % if the same water were in a smaller glass?
How to measure humidity - Sling Psychrometer • Remember - evaporation cools things (sweat, misters in outdoor cafes, etc.) • Evaporation goes faster in dry air. • The drier the air - the greater the difference between wet and dry-bulb temperatures.
Hair Hygrometer - • Hair changes length depending on humidity - “bad hair days”!
Cold is air’s kryptonite • Warm air can hold more moisture. • Cold air holds less moisture. • So, cooling air reduces the air’s ability to hold moisture, and if that air was holding a lot of moisture, it may drop moisture (condensation). • What happens to RH if you warm the air?
Dew point - • The temperature that you have to cool air to in order to make the air drop its moisture is the dew point. • RH = 100% at DP. • Is dew point high or low on a dry day?
If you cool air to its dew point, condensation happens. • If you breathe on cold glass, moisture from your breath ____________ on the glass. • If you cool air up in the sky to its dew point, water vapor condenses into ___________. • If you cool air near ground level to its dew point, ______ forms. • On cool mornings, _____ forms on cool grass. • If the dew point is below freezing (32f or 0c) and the air gets that cold , _______ would form on grass instead of dew.
