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It's Not the Heat, It's The Humidity: Study of Humidity

Lesson Objectives
Related National Standards
Tools and Materials Needed
Estimated Time to Complete Lesson
Teaching Strategy
Procedure
Helpful Web Sites
Assessment Recommendations
Extensions/Adaptations

Lesson Objectives

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:

  1. Calculate the dew point from temperature readings.
  2. Understand one reason for the large number of clouds in Borneo.
  3. Use Internet resources to chart heat and relative humidity in a selected area of Borneo.

Subjects

Meteorology, physical science, life science, geography

Grade Level

Elementary and above.

Related National Standards from the McRel Standards Database

http://www.mcrel.org/standards-benchmarks/

Science

  1. Understands how species depend on one another and on the environment for survival.
  2. Knows the processes involved in the water cycle (e.g., evaporation, condensation, precipitation, surface run-off, percolation) and their effects on climatic patterns.
  3. Knows that water can change from one state to another (solid, liquid, gas) through various processes (e.g., freezing, condensation, precipitation, evaporation).
  4. Knows that clouds and fog are made of tiny droplets of water.

Tools and Materials Needed

  1. copy of the program "Borneo: Island in the Clouds"
  2. empty silver can, soup can size
  3. thermometer
  4. ice
  5. water vapor in saturated air chart

Estimated Time to Complete Lesson

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.

Teaching Strategy

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:

Relative humidity = (Amount of water in the air/Amount of water the air could hold) x 100

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.

Video Segments

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.

Procedure

  1. Watch the "Living Edens: Borneo" video. List the influence of water throughout the video. Emphasize the importance of the water from cloud droplets, as an erosion force, as a distributor of energy and as a necessary component of life. At the start of the film, review the bathing of the forest in fog, the evaporation of the fog as the sun appears and the rolling cloud banks by the mountains. Throughout the video, identify organisms that live at various levels in the forest.
  2. Have students record the air temperature and chart the data. It is easiest to do this for the first time inside the classroom but other readings should be taken outside.
  3. Take a soup can of tepid water and determine the temperature. Put in a few pieces of ice and stir the water. As the can becomes cooler, watch for the first appearance of a water film on the side of the can. Record the temperature, called the dew point, when the film first appears.
  4. Consult the chart and find the amount of water vapor that could be held in a cubic meter of air at each temperature. The values are placed in the formula to determine the relative humidity. Students should graph the relative humidity, the daily high temperature and the daily low temperature for a period of weeks. The Weather Underground site can give you the temperature and relative humidity readings to plot the values for Borneo. Student groups may be set up to compare reading from Borneo with that of a desert and their own location.

Amount of Water Air Can Hold At Various Temperatures

Temperature in Celsius

3
-2
-1
0
1
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32

Grams of water vapor in a cubic meter

3.7
4.0
4.4
4.8
5.2
6.0
6.4
7.5
8.1
9.3
10.7
11.4
13.0
16.0
18.2
19.4
22.0
23.5
25.0
30.0
34.0

Helpful Web Sites

Weather Underground
http://www.wunderground.com/global/SK.html
The Weather Underground: Sarawak contains all the information you need for students to calculate dew point and check the calculations for the rainforest of Borneo. From here, it is easy to enter the location of any place on earth to obtain weather data to plot.

Borneo Online
http://www.borneo-online.com.my/
Borneo Online has a wealth of information about the island, including weather data. This site will provide answers and links for most questions about Borneo.

Assessment Recommendations

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.)

Extensions/Adaptations

  1. Younger students can better understand the cycle of water by making a simple model in a closeable storage bag. Take a half a medicine cup of water containing one drop of food coloring and place it in the corner of a bag without spilling the contents. Zip the closure on the bag and tape it to a window in the sun. The water will evaporate from the cup, go into the air in the bag and collect on the walls of the bag. In a short time, drops will form and rundown to the bottom of the bag to form a clear puddle.
  2. Older students can use the dew point and the temperature to calculate the height to the base of clouds. Air temperature has been found to decrease with altitude at the rate of 10 degrees C/kilometer. The dew point has been determined to decrease at a rate of 2 degrees C per kilometer. Students can use centimeter graph paper to determine the height of cloud bases. On the left side of the graph (Y axis), students will plot an altitude scale that should go from 0 kilometers to 5 kilometers. The X axis is used for a temperature scale that should run from 10 degrees C to 40 degrees C. Since the temperature and dew point decrease at a standard rate, the proper temperatures can be determined for various altitudes and a line plotted. The place that the two lines cross is the point that the dew point is equal to the air temperature. The altitude of the cloud bases occurs at this point and can be read directly off of the scale.



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