By Susan Frack and Scott Prickett
All life on earth depends on water in some way. The earth's water must be "recycled" from one use to another. It must be moved through the earth and the atmosphere to accomplish this. This movement is the "Water Cycle".
The water exists as a vapor, liquid, or a solid. 98% of the water is in liquid form. It can be easily changed from form to form using heat energy. Changing from vapor to liquid is called condensation: from liquid to vapor is called evaporation; and from liquid to solid is freezing.
The water in vapor form in the atmosphere is better known as humidity. It can be measured using a sling psychrometer. At a given temperature, there is a maximum amount of humidity that can exist in the air. If the air is holding this maximum amount it is saturated. Some of the humidity will begin to condense on solid surfaces as dew or frost or small droplets in the atmosphere to form clouds. As the clouds become saturated with water droplets, they become too full/heavy and the droplets fall to ground as precipitation of some type. Liquid precipitation is measured with a rain gauge.
Changes in the temperature of the atmosphere play a key role in determining the rate of evaporation and condensation within the water cycle.
- TV and VCR
- poster paper
- several potted plants
- gallon size plastic bags
- heat lamp
- sling psychrometer
- rain gauge
TLW: Nat. Sci. Obj.
- Describe the movement of water through the water cycle. A,B
- Describe how clouds form. D,E
- Explain relative humidity and demonstrate how to measure it. F,G
- Compare conditions that allow different forms of precipitation to form.
- Practice measuring precipitation. Nebraska Frameworks Obj.: H-1, H-7
Watch the movie, "Grand Canyon Suite",(available from Disney Productions or in some video stores) concentrating on the section where it rains, clears up, evaporation happens, etc. This is a great illustration of the water cycle. If it is unavailable, look for a series of pictures or slides that would show the same sequence of events (clouds form a thunderstorm, rain occurs, clouds dissipate, sun comes out and dries up the puddles). You can also set up a demonstration using a brick, sprinkling can and a blow dryer. Heat the brick with the blow dryer, sprinkle the brick with water, and use the blow dryer to evaporate the water quickly. After the movie, etc., have the students list the steps of what happened on the large piece of poster paper. If they would like to illustrate as they go or do more research-COOL!--you want them to figure out what caused the rain, the sun coming out and the evaporation.
I. 1. Using the Jigsaw method of cooperative learning (see directions below), have students study the 5 parts of the water cycle: condensation, evaporation, infiltration, precipitation, and runoff. This method is structured such that each student brings a different piece of information to the team and the whole team can complete the activity only with all the information. Before participating in the team activity of acting out the water cycle, each student will study a small bit of information in a jigsaw group with students from other teams who have been assigned the same component of the water cycle. The easiest way to make a jigsaw work is to organize teams of 5 and pass out the jigsaw assignment together. When students have finished their assignment in the jigsaw, they take the information learned back to their original teams to complete the activity. The activity is to act out their part in the water cycle as a pantomime and have their group members guess what they are doing .
A. Divide class into 4 groups of 5.These are their "home groups". Label the classroom with directions-N,S,E,W- and locate 1 home group at each direction. Give each group member one of the 5 cards with information on it.(see appendix A) If there uneven numbers of students, there can be 6 to group with 2 people receiving the number 2 card.
B. Have all the card #1 people move to 1 location, the #2's to a different location and so on. Allow 5-10 minutes for each group to read and discuss the material and prepare a pantomime that they will do for their "home group". Remind them that they can not use any words, but can make sounds and use hand/body movements for the pantomimes.
C. Call time and have students return to their "home groups" to do their pantomimes. Then they should develop a play illustrating the water cycle with all of its processes in action. After 5-10 minutes for teams to get organized and see where their cycles work in their areas, have all teams begin their cycles.
D. The classroom should then be representative of the world with water cycles going on in many/several locations. 2. Calm the room down after about 3-5 minutes of "cycles" and bring the groups together as a class and discuss what happened. Concepts that you should enforce are: the water cycle is continuous water cycle can happen anywhere if there is evaporation, condensation , and precipitation water cycle can be interrupted/changed/affected by man's actions 3. Reinforce the processes of cloud formation if necessary.
Make a Cloud Lab--see appendix II.
1. Bring in several house plants. Be sure the soil is moist. Cover them with clear plastic bags. Put them under a heat lamp for several hours. Explain to the students that you are going to try to get some condensation to form on the surface of the bag. Turn off the lamp and let the plants sit overnight. A nice collection of condensation should form on the bag and the plant leaves--or you can use a terrarium if you have one. Discuss with the kids where the condensation came from and what conditions caused it to appear. Through the discussion and possible research, introduce and define the following terms/concepts: humidity and relative humidity saturated air saturation temperature/dew point
2. Display the sling psychrometer and have students examine it to propose theories of its use. Let each group share their ideas. Then show its actual use and so some sample problems on how to find relative humidity so students get the idea. Proceed with lab on relative humidity--appendix B. (Information on how the sling psychrometer works is found in appendix C) ADDITIONAL ACTIVITIES: Finding the Dew Point lab--Project Earth Science: Meteorology, P. Shawn Smith and Brent A. Ford, NSTA Publications, 1994. III. 1. Have students read/research the different types of precipitation and complete the Precipitation Chart--appendix D. 2. Mount the rain gauge on a post on the school grounds so that it is at the students' eye level. Explain how to use it or use the Hyper Studio program as a tutorial. (Information on measuring rain/snow is in appendix C.) 3. Keep track of precipitation and relative humidity for 2 weeks.
Hail in a Test Tube Rainy Day Tales Project Earth Science: Meteorology, P. Shawn Smith and Brent A. Ford, NSTA Publications, 1994 EVALUATION: use any or all or none!! A. Build a working model of the water cycle B. Make a poster that explains the different forms of precipitation. C. Design a Hyper Studio or similar program that illustrates: evaporation, humidity, cloud formation, condensation, precipitation etc.
CARD 1: CONDENSATION
Condensation occurs when a gas is changed to a liquid. In the water cycle this occurs when invisible water vapor changes into liquid water. This process is essential for clouds to form. As the water vapor in the atmosphere rises, the temperature of the atmosphere decreases. The warm, moist air meets the colder, drier air and forms tiny drops of water. For this condensation to occur there must be a surface available to which the individual water molecules can stick. Condensation surfaces are small particle of matter such as dust and other chemical compounds suspended in the atmosphere, and larger drops of water. The layers of warm and cold air mix to form clouds. Very high clouds will be so cold that the water droplets will change to ice crystals. Lower clouds will be warmer and the water droplets will clump together to form larger rain drops.
CARD 2: EVAPORATION
Evaporation is the process of changing a liquid to a gas. In the water cycle, the sun's energy transports water from land, plants, and water surfaces to the atmosphere as water vapor: the water molecules are heated up and move apart from their source. Water evaporates from the ocean, rivers, lakes, soil, plants, and swimming pools. Water vapor is added to the atmosphere from plants through processes known as respiration and transpiration. Although in much smaller volumes, water vapor is also added to the atmosphere from the breathing of humans and other animals, and from machine combustion and the cooling towers of electrical generators. Evapotranspiration describes the total water loss from the earth's surface.
CARD 3: PERCOLATION
Most precipitation that reaches the ground flows into the soil. Percolation is the process of water seeping downward from the surface of the earth into the soil and rocks and becoming groundwater. Plants use some of this groundwater but most of it collects in pore spaces around soil and sediments and in rocks in areas called aquifers. This water is pumped to the surface by humans for use. In some places, the groundwater reaches the surface by itself as a natural spring. It can remain in the ground for hundreds of years before it is used.
CARD 4: PRECIPITATION
Precipitation occurs after water vapor condenses into droplets and the droplets get heavy enough to fall to the earth's surface from the clouds. Water droplets collide with each other in the clouds to form larger drops. Gravity and/or a drop in temperature make them too heavy for the cloud to hold. Precipitation can be found in either a solid or liquid state depending upon the temperature. Rain, snow, sleet, snow, and hail are common forms of precipitation. In the desert it is common to see rain that is falling evaporate before it reaches the ground. This precipitation is called virga.
CARD 5: SURFACE RUNOFF
Surface water is all the standing/moving water found on the earth's surface. It includes water in oceans, lakes, rivers, ponds, marshes, swamps, glaciers, snow fields, etc. Runoff is the liquid water that drains off the surface of the land during precipitation and collects in one place. Runoff can be trapped and stored in reservoirs to be used by man. Human uses include: industrial, household, agricultural, and recreational.
APPENDIX B - DETERMINING RELATIVE HUMIDITY OBJECTIVE:
To find the relative humidity in different locations of the school building.
- 1 sling psychrometer per group of students
- eye dropper
- small cup of distilled water, at room temperature
- Assemble the sling psychrometer if necessary.
- Wet the gauze on the wet bulb thermometer with the eye dropper. Twirl the psychrometer gently to remove excess water from the gauze.
- Gently spin the psychrometer for one minute in each of the locations listed on the data chart. Record the dry-bulb temperature and the wet-bulb temperature of each location on the data chart . Use Celsius degrees. You should re-wet the gauze at each location.
- Calculate the difference between the wet-bulb and dry-bulb temperatures and record it on the data chart. Then compare the dry bulb temperature and the difference on the relative humidity chart to find the relative humidity for each location. Record this relative humidity.
- Make a bar graph to compare the humidity of each location.
- Answer questions about humidity.
- Which thermometer measures the air temperature? Explain:
- What is the relation ship between evaporation and the wet-bulb thermometer's temperature?
- What is the relationship between evaporation and relative humidity?
- Where was the relative humidity the lowest? Why?
- Where was the relative humidity the highest? Why?
- Did a pattern develop in the relative humidity readings in the school? Explain:
- What would the relative humidity be if both the dry and the wet bulb had the same temperature? Explain:
- Explain, in your own words, how to find relative humidity:
APPENDIX C - THE PSYCHROMETER:
It has two thermometers. One thermometer is dry, or dry-bulb, giving the air temperature. The second thermometer has a distilled water-soaked piece of cloth fastened over the bulb to give the wet-bulb temperature. The instrument is whirled around by a handle for 1 minute or so. Evaporation causes the wet-bulb temperature to be cooler. Relative humidity is found by finding the difference between the 2 thermometers and comparing this difference with the dry bulb reading on a chart. If the relative humidity is 100%, there will be no difference between the 2 thermometers.
THE RAIN GAUGE:
The rain gauge is thought to be the oldest weather instrument. Almost any straight walled container can be used to collect rain. The standard gauge catches rain in a funnel whose mouth is exactly 10 times larger than its tube that the rain is deposited into. Measuring snow is simple: push a measuring stick into the accumulated snow in 3 widely differing locations and find the average of the 3 amounts of snow.
APPENDIX D PRECIPITATION TABLE: TYPE of PRECIPITATION TEMP TO FORM DESCRIPTION RAIN SLEET HAIL SNOW
APPENDIX E: MAKE A CLOUD OBJECTIVE:
To create the conditions necessary for a cloud to form. MATERIALS: wide-mouth glass jar at least 20cm tall large balloon large rubber band hot water wood splint or long kitchen matches
Cut the balloon open and stretch across the mouth of the jar. Secure it with the rubber band. Push down in the middle of the balloon with your fingers and release. Observe the inside of the jar and record any changes that occur. Remove the balloon and fill the jar with hot water. Empty the jar and replace the balloon quickly. Repeat step 2. Remove the balloon. Put a burning match/splint into the jar until it goes out. Quickly replace the balloon. Repeat step 2.
Step Observations 2 5 8
- What filled the jar after you poured out the hot water?
- What did the burning match/splint add to the jar?
- What conditions produced the best cloud? Why?