How to Make a Hygrometer: Sling Psychrometer
First of all, what is a hygrometer and why would you want to make one? A hygrometer is a tool used by meteorologists (scientists who study the weather) to measure how much moisture is in the air.
You might have heard an older person say “It’s the humidity, not the heat” on one of those days in early August when walking from the couch to the refrigerator is a major effort. Humidity is the amount of water vapor (moisture) in the air. We become exhausted on hot, humid days because we can’t sweat efficiently. The air is already so full of water, little sweat evaporates off our skin to cool us. Instead, we feel sticky and hot. On dry summer days, or in the desert, the temperature might be just as high, but we won’t feel as uncomfortable because the humidity is lower. Meteorologists created a term to describe quantitatively how full of water vapor the air called relative humidity. It is the ratio of the actual amount of water vapor in the air relative to the amount that could be there, at that temperature. If you ever have walked through fog, you have experienced 100 percent humidity. Humidity levels in the desert are often 10 percent.
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