Theoretical material for the lesson, definitions for concepts 

Relative Humidity

The amount of water vapor in the air at any given time is usually less than that required to saturate the air. The relative humidity is the percent of saturation humidity, generally calculated in relation to saturated vapor density.

The most common units for vapor density are gm/m3. For example, if the actual vapor density is 10 g/m3 at 20°C compared to the saturation vapor density at that temperature of 17.3 g/m3 , then the relative humidity is 

Relative humidity is the amount of moisture in the air compared to what the air can "hold" at that temperature. When the air can't "hold" all the moisture, then it condenses as dew.

Dewpoint

If the air is gradually cooled while maintaining the moisture content constant, the relative humidity will rise until it reaches 100%. This temperature, at which the moisture content in the air will saturate the air, is called the dew point . If the air is cooled further, some of the moisture will condense.

Interesting facts about humidity

1. Fifty percent humidity is a sponge half full.

Humidity describes the amount of water vapor or water molecules in the air. Weather scientists use the term “relative humidity,” which Joe Sobel, a meteorologist and senior vice president at Accuweather described as “a comparison of the amount of moisture in the air versus the amount of moisture the air could hold.”

Think of the atmosphere as a sponge that can hold a fixed amount of water, let’s say a gallon of water. “If there is no water in the sponge… then the relative humidity would be zero,” Sobel said. Saturate the sponge with half a gallon of water – half of what it is capable of holding – and that relative humidity climbs to 50 percent.

“The amount of moisture that the atmosphere can hold relates directly depends on the temperature,” Sobel said. Think of a rise in temperature like an increase in sponge size. A sponge that is half saturated with water is at 50 percent humidity. Now, increase the size of the sponge without adding more water. The relative humidity decreases because the bigger sponge is capable of taking on more moisture, but the same amount of water remains.

Soaking a sponge with more water than it can hold would cause it to drip. But this dripping doesn’t always symbolize rainfall. The relative humidity measured on the ground (where the sponge is) doesn’t reflect moisture levels miles above in the sky. Rain occurs when the rising air can no longer hold the water droplets that have formed clouds high in the sky. (Clouds can form closer to the ground too — that’s fog). The temperature and atmospheric pressure changes as you ascend into the sky — the air gets colder and thinner. So 100 percent humidity might not mean rain, but it does mean dew.

2. What’s the deal with dew?

Dew occurs when the relative humidity reaches 100 percent.

“Dew point temperature is an absolute measure of the amount of water vapor in the air,” Sobel said. If you have a dew point temperature of 65, that means that the outside temperature must decrease to 65 degrees before dew, or water, will form on your lawn. And if the temperature outside is 65 and the dew point is 65, then the relative humidity is 100 percent.

Dew point temperature is a good indicator of how comfortable or how uncomfortable you might feel, Sobel said. But we don’t hear about it on the Weather Channel. It does, however, get calculated into the “RealFeel” temperature along with other factors like wind, cloud cover and the angle of the sun.

3. Humidity brought us tonal language.

Our vocal cords are comprised of a pair of mucus membranes that stretch across the voice box, or larynx. They vibrate, controlling the air from the lungs that flows by as we speak or sing. The level of moisture in the air affects the elasticity of our vocal cords. Singers can tell you that it is harder to carry a tune in a dry environment.

We’ve known for decades that you are more likely to be on pitch in humid environments. More recently, researchers theorized that speech was one of many human behaviors adapted to fit environment. After looking at more than 3,700 languages, they discovered that tonal languages, like Chinese and Vietnamese, rarely developed in dry climates.

https://www.pbs.org/newshour/science/8-things-didnt-know-humidity

Additional guidelines for organizing a lesson 

Feedback: teacher-student, student-student 

Define the topic of the lesson and lesson’s objectives.

Task: humidity worksheet

Teacher’s action: organize the students’ work, and check student’s work.

Key

1 Dew point of 65 degrees

2 air is saturated

3 80 degree air

4 Air that is 75% full

5 Air that has a relative humidity of 75 %

6 Both would have the same amount.

7 The one with the higher temperature

8 the measure of how full of water air is compared to how much it can hold

9  temperature

10 goes up

11  decreases

Useful links

https://science.howstuffworks.com/nature/climate-weather/atmospheric/question6511.htm

https://wonderopolis.org/wonder/what-is-humidity

https://www.pbs.org/newshour/science/8-things-didnt-know-humidity

https://www.youtube.com/watch?v=FF9WTjUXK3k

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