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what is humidity

Have you ever visited a place that just made you feel hot and sticky the entire time, no matter what you did to cool off?

Humidity is the amount of water vapor in the air. If there is a lot of water vapor in the air, the humidity will be high. The higher the humidity, the wetter it feels outside.

On the weather reports, humidity is usually explained as relative humidity. Relative humidity is the amount of water vapor actually in the air, expressed as a percentage of the maximum amount of water vapor the air can hold at the same temperature. Think of the air at a chilly -10 degrees Celsius (14 degrees Fahrenheit). At that temperature, the air can hold, at most, 2.2 grams of water per cubic meter. So if there are 2.2 grams of water per cubic meter when its -10 degrees Celsius outside, we’re at an uncomfortable 100 percent relative humidity. If there was 1.1 grams of water in the air at -10 degrees Celsius, we’re at 50 percent relative humidity.

When humidity is high, the air is so clogged with water vapor that there isnt room for much else. If you sweat when its humid, it can be hard to cool off because your sweat cant evaporate into the air like it needs to.

Humidity is blamed for all kinds of negative things, including mold in your house (usually the bathroom, where its wet a lot of the time), as well as malfunctions in regular household electronics. Moisture from humid air settles, or condenses, on electronics. This can interrupt the electric current, causing a loss of power. Computers and television sets can lose power like this if not protected from the effects of humidity. Living with humidity is easier with the aid of a dehumidifier, which sucks moisture out of the air.

High humidity is also associated with hurricanes. Air with high moisture content is necessary for a hurricane to develop. U.S. states such as Texas and Louisiana, which border the very warm Gulf of Mexico, have humid climates. This results in tons of rainfall, lots of flooding and the occasional hurricane.

Try It Out

Ready to get some hands-on experience with humidity? Find a friend or family member to help you explore one or more of the following activities:

  • Spend some time watching local weather forecasts. You can watch them on television on the nightly news. Or, if you prefer, you can read them in a local paper or even find them online at a variety of weather information sites. Do you understand all the weather-related terms the forecasters use? If not, ask an adult to help you understand what any unfamiliar terms mean. Keep an eye on the weather the next day. How accurate was the forecast?
  • You’ve probably felt how a hot day can feel even hotter when it’s really humid outside. Here’s a little experiment that will help you understand why. Soak a washcloth in a bowl of warm water. Wring out the water so that none drips out but the washcloth is still warm. Feel the warmth of the washcloth. Now wave the washcloth around in the air for a bit. When you’re finished, feel the washcloth again. Does it feel cooler? It should. As moisture evaporates, it carries heat with it. When you waved the washcloth around in the air, water evaporated from it, taking heat with it and making the washcloth cooler. A similar thing happens in the air. When water vapor remains in the air as humidity, it makes the temperature feel warmer. As the humidity lowers, the air feels cooler!
  • Can you really feel the difference when relative humidity fluctuates? Keep track and see for yourself. Over the course of a few weeks, keep a daily weather log. Record the actual temperature and the relative humidity. Also record how the weather feels to you. Before finding out what the actual temperature and relative humidity are, make a guess as to what temperature you think it is. How accurate are your guesses? Do your guesses tend to vary with the relative humidity? If you’re up for a real challenge, create a graph that compares your guesses with the relative humidity for each day to see if there’s a correlation.

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