It's Not the Heat, It's The Humidity: Study of Humidity
Students will calculate the relative humidity outside the school using simple materials. The readings will be charted and graphed to look for trends in the data. Students will understand that the air can hold a limited amount of water, that temperature determines the amount of water that can be held and that the water moderates the temperature in an area. By relating the relative humidity to the video, students will see a way other than rain that organisms in the forest receive moisture.
By the end of this activity, students will:
Meteorology, physical science, life science, geography
Elementary and above.
Approximately one week. One class period to watch the video. One class period to determine the relative humidity of their area for the first time. About 10 minutes on subsequent days for the class to take temperature readings and plot temperature and relative humidity data. Graphing the data for a month or more shows the best patterns for the area being studied.
Background Information: Relative humidity is a percentage that tells how much water is in the air at a certain time compared to what it could hold. It may change from day to day or even from hour to hour and is mainly dependent on the temperature. When the relative humidity is high, there is a great deal of moisture and so the air does not have the ability to absorb much more water. This is why rainforests feel hot and sticky to a visitor. At night, the falling temperatures cause the air to be able to hold less water than during the hotter day and some of the water must come out of the air.
Scientists have put relative humidity into a simple formula. This formula is:
Warmer air can hold more water than colder air. The chart displays the number of grams of water that a cubic meter of air can hold at that temperature. Notice that as you look down the columns both the temperatures and the numbers opposite them get bigger. Students will look up both the amount of water that can be held at room temperature and the amount of water that can be held at the dew point temperature for use in the formula.
For example: The outside temperature is 20 degrees C and the dew point is 10 degrees C. What is the relative humidity? From looking at the chart, the outside temperature tells us that the air has the ability to hold 18.2 grams of water in a cubic meter. From looking at the chart, the dew point tells us that the air is currently holding 9.3 grams of water in a cubic meter. By using the formula, it is found that the relative humidity is 51%. This means that the air can hold twice as much water as it is now holding. When the dew point temperature is equal to the air temperature, the air is holding as much water as possible. If the temperature drops even a little bit, some of the water it is holding must come out in the form of dew, frost, fog or cloud.
Without clouds, it would not be possible for the rainforest to exist. While we think of almost daily rains bringing moisture to the lands, we often forget that the leaves channel the water and leave areas almost dry. The bath of fog brings moisture to every part of the rainforest from hidden tree branches and trunks, to the inside of flowers. Due to the high temperatures, the air can store and retain a large amount of moisture during the day, and then it is released at night. Even small puddles created inside of some flowers can harbor eggs and small animals.
The water in the air serves as a heat sink that moderates the temperature. By graphing the humidity and the daily high and low temperatures, we can see the low amount of fluctuation in the daily temperatures.
As the warm, moist air is pushed up a mountainside, the air cools and reaches the dew point enabling a cloud to form. As the air reaches the peak of the mountain and begins to descend, it warms and the cloud evaporates. This is one of the reasons for clouds covering the tops of mountain ranges. In mountain chains, it causes one side of the mountain to be significantly wetter than the opposite side.
2:00 Clouds in the rainforest cover the trees then evaporate as the sun comes out. The video then goes to the clouds by the tops of Mt. Kinabalu which evaporate as they reach drier air at the top of the mountain. Clouds and water are a theme that repeats throughout the show.
Amount of Water Air Can Hold At Various
Students may be assessed though their participation in the class discussion of the video. Students will be able to be assessed on the determination of relative humidity and the charting and graphing of the information on an objective basis. Students should write a paragraph explaining how high and low relative humidity affects the temperature fluctuation. (On days of high relative humidity the temperatures will change less than days of lower relative humidity.)
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