By Susan M. Frack and Scott Prickett
Much of the earth is covered with water. As the water is warmed by the sun, some of it will evaporate and become water vapor in the atmosphere. This water vapor is called humidity. When there is a large amount of water vapor or humidity in the air the air feels sticky. If there is a small mount of humidity in the air, the air feels dry.
When the sun goes down, the air cools off and the water vapor collects on cool surfaces like leaves, grasses and buildings. It is now called dew. If it is below freezing outside, this dew will become frost.
High in the sky, the water vapor begins to cool off and from tiny droplets. these droplets join together to make clouds. When the droplets in the clouds become too heavy, they fall back to earth as rain. It takes many tiny droplets to form 1 rain drop. If the temperatures is below freezing, the droplets will freeze into crystals called snowflakes before they fall. Sleet will form if the rain drops fall through freezing air on their way to the ground.
The cycle of evaporation, forming clouds, and precipitation is called the “Water Cycle”. Scientists use a hygrometer or a sling psychrometer to measure humidity and a rain gauge to measure liquid precipitation.
- TV and VCR
- brick or clay flowerpot
- cake pan
- blow dryer
- spray bottle
- chart or poster paper
- clear tape
- coffee can
- collection of different rain gauges
- demonstrate the steps of evaporation, cloud formation, and precipitation within the water cycle.
- make and demonstrate how to use a hygrometer to record daily humidity.
- describe how rain, snow, and sleet form.
- show how to use a rain gauge to record daily precipitation.
Explain to the children they are going to see something that happens in nature. Ask them to think about what is happening as they watch. Ask them to be ready to talk about what they see and be ready to ask/answer questions.
A. Watch the movie, “Grand Canyon Suite” (a Disney movie available at most ESU’s). It shows the beginning of a thunderstorm, the thunderstorm, and the sun coming out afterward and evaporating the water. (the Water Cycle)
B. Show a series of pictures that would show the clouds building for a thunderstorm, the thunderstorm, the sun coming out, and the rain drying up.
C. Set up the following demonstration:
- Put the brick or flower pot in the cake pan and spray with water to simulate rain.
- Use a blow dryer to be the sun and wind and blow over the cake pan. the water should begin to evaporate.
- Ask the children to describe what they saw happening in the movie, pictures, or demonstration. Encourage everyone to respond. Older students may want to make a list on board.
- Begin to categorize the happenings into the general areas of : evaporation/drying up, cloud formation, and precipitation.
- Introduce the term, “Water Cycle”. Show how the 3 previously mentioned categories form a cycle:
- This cycle can be shown with a flannel board, drawings on the board, etc. (Sample drawings and flannel board patterns are included in Appendix A).
- Have students make their won water cycle picture/poster. Younger students can use precut pieces and place them on a template or draw their own. Older students can cut out pieces, or find appropriate magazine pictures to use.
- write poetry or stories about raindrops and clouds
- sing rain songs
- count/add/subtract/etc. with raindrops or clouds
Develop the concept of humidity by spraying the group lightly with the spray bottle. Go back to the water cycle diagram-evaporation step and review how water gets into the atmosphere.
- Have students talk about their experiences with humidity:
- makes you feel sweaty and sticky
- makes your hair frizzy
- makes the bathroom foggy if the door is closed when you take a shower
- Return to the curly/frizzy hair idea and explain that they are going to make an instrument called a hygrometer, that will measure humidity, out of a human hair. Very young children will do this as a class project and make 1 hygrometer for the class or just observe what the teacher does. Older students should be divided into groups and allow to complete the activity within their groups. See HYGROMETER activity in Appendix C.
- Keep track of the humidity for 2 weeks. You cannot report humidity on the STEDII page using a hygrometer. Just enter the code for “no data” for humidity.
- Give each student a cup with an ice cube in it. Ask them to pick up the ice cube and hold it in their hand for a little bit. Have them hold long enough for it to begin to melt and drip. Have students tell what happened. Observations should be listed on board. Now talk about why the ice cube changed warmth from the air and their hands melted it. Ask how they could get the ice cube “back together” like it was before it melted--refreeze. Ask what would happen to the drops that don't get into the ice cube evaporate, freeze, etc.
- Go back to the water cycle and look at the precipitation step and differentiate now between the conditions necessary to form rain, snow, and sleet:
- Rain--tiny water droplets form into heavier drops and fall
- Snow--water droplets freeze into snowflakes
- Sleet--raindrops fall through freezing cold air and freeze into sleet.
- Make a class poster to show this what happens when temperatures are above freezing, below freezing, and forming raindrops.
- make snowflakes
- Try to collect several different rainguages to show--ask students to bring them in as well. Also have coffee can with a ruler in it to show how simple a rain gauge can be.
- Let the students examine the gauges for some time. Then establish their use--collecting rain. Tell the students that the rain gauge is probably the oldest weather device still in use today. Discuss the similarities/differences between the gauges.
- Let students then experiment with water and measuring in the gauges. Be sure to remove any delicate/glass gauges so they won’t be damaged. You can have them measure specific amounts as well as place mystery mounts in the gauges and have their friends tell how much is in the gauge. Instruct them to hold the gauge at eye level to read the amount.
- Have a gauge mounted at the students’ eye level on a post on your school ground. Add water to the gauge and have students practice reading it. be sure to explain the unit that gauge is measured in and that their measurements should always be given with the number and the unit. Discuss why--such a variety of gauges are available and all of them measure differently.
- Keep track of the daily amount of precipitation for 2 weeks. For measuring snow, simply push a centimeter ruler into the snow and read the depth.
Students will use the flannel board/poster pieces(Appendix D) to tell the water cycle to their teacher. Students will color and cut their own pieces so they can take them home and tell their family the story as well. Be sure to ask students to tell about “humidity”, “how snow and rain form”, and how “clouds form’ as they go through their explanation.
Read weather stories:
- The Storm Book by Charlotte Zolotow
- What Will the Weather Be Like Today? by Paul Roger