TOPIC C:
Water In the Air
ACTIVITY #1: What are Dewpoint and Relative Humidity?
TYPE OF ACTIVITY: Small Group
MATERIALS NEEDED PER GROUP: metal can with shiny surface,
thermometer, water, ice, newspaper, worksheet #3.
DESCRIPTION:
Students will learn about dewpoint and relative humidity by measuring
them with the chilled mirror method.
BACKGROUND INFORMATION FOR TEACHER: One of the ways in
which meteorologist report the amount of water vapor present in
the air is by giving the dewpoint temperature. This is a more
direct method of reporting that is not as dependent upon air temperature
as is relative humidity.
The total amount of water vapor that the air can hold depends
upon its temperature. The warmer the air, the more water vapor
it can hold. When the air contains all of the water it can hold,
we say that it is saturated. In other words, the relative humidity
of the air is 100%. Water vapor is removed from the air through
condensation. If the drops of water formed by this process are
small enough to float in the air we call it fog (or clouds). If
the water collects on the ground and other surfaces, we call it
dew, or frost if it is frozen.
The chilled mirror method involves cooling a shiny surface until
water condenses on it. The temperature at which this occurs is
the dewpoint temperature.
It doesn't matter how much or how little water vapor is in the
air. Ultimately, the air can be cooled down to the point where
it is saturated. The temperature at which saturation occurs is
called the dewpoint temperature. When reporting relative humidity
we're referring to how far the air is from saturation. If it contains
half the water vapor it is capable of holding, its relative humidity
is 50% at 40 degrees. This can easily be seen by comparing dewpoints
(dewpoint is 69 degrees for 90 degree air, and 24 degrees for
40 degree air).
Measuring the dewpoint is important to forecasting. High dewpoints
indicate a better chance of rain. When forecasting morning lows
it is important to remember that the temperature cannot drop below
the dewpoint. Furthermore, dry air will experience larger temperature
swings from day to night than humid air.
INSTRUCTIONS:
|
TEACHER |
STUDENTS |
| 1. If possible, divide students into groups of two or three | |
| 2. Have one student from
each group fill the can about halfway with water at or near room temperature. |
2. Fill your can about halfway with water. Make sure the outside of your can is clean and dry. |
| 3. Be sure the students place their cans on steady surfaces. | 3. Set the can down on
a steady surface. Putting a piece of newspaper underneath the
can may make viewing easier. |
| 4. Help the students read their thermometers if needed. | 4. Place the thermometer in the water and measure its temperature. Write this number down. |
| 5. Give the students ice and instruct them to add it to the water a little bit at a time. | 5. Add a little bit of ice to the water and gently stir. |
| 6. Watch the students
and make sure they don't add ice too quickly or break the thermometers. Help students to notice the first signs of condensation on their cans and read their thermometers. |
6. Watch the outside
surface of the can for the first sign of condensation. If the
first piece of ice melts before this happens, slowly add more ice. When the condensation is first noticed read the thermometer. Write this number down. This is the dewpoint temperature. |
| 7. Help students determine that the water or "sweat" on the outside of their cans came from the air around the cans. Guide them toward the realization that this is the same process that results in dew and frost formation. | 7. Where did the water
on the outside of the can come from? Have you ever noticed this
sort of thing happening before? |
| 8. Compare temperatures collected by all groups to come up with an average dewpoint temperature for the class. | 8. Share the value you measured for dewpoint with the rest of the class. How do they compare? |
| 9. Using the air temperature and dewpoint just measured, find the relative humidity on the chart. | 9. Determine the relative humidity of the air using the numbers you just measured. |
TOPIC C: Water In the Air
ACTIVITY #2: Using a Sling Psychrometer
TYPE OF ACTIVITY: Large Group
MATERIALS NEEDED: sling psychrometer, water in a spray bottle, worksheet #4, worksheet #5
DESCRIPTION: Students will learn to measure humidity with a sling psychrometer.
BACKGROUND INFORMATION FOR THE TEACHER: Meteorologists use a variety of methods to measure dewpoint. The method used in the previous activity involved the use of a chilled mirror for a direct measure of dewpoint.
This activity uses a less direct but very common method of measurement, use of the sling psychrometer. For this method we use two thermometers--one to measure air temperature or "dry-bulb" and the other to measure "wet-bulb" temperature. The bulb thermometer take advantage of the effects of evaporating cooling which will also be investigated in this activity. When water evaporates off of a surface that surface cools. The lowest temperature in can reach is its wet bulb temperature.
INSTRUCTIONS:
|
TEACHER |
STUDENTS |
| 1. Have students wave both hands quickly through the air. Ask them how they feel temperature-wise. | 1. Wave both hands in the air. Is one hand different in temperature than the other? |
| 2. Have each student spray some water on one hand. | 2. Spray a little water on one of your hands. |
| 3. Have students wave both hands in the air again. Ask them how they feel now. (Wet had should be cooler.) | 3. Wave both hands in the air again. How do they feel now? |
| 4. Explain to the students that their hands just functioned in exactly the same fashion as the psychrometer. | |
| 5. Show students the psychrometer and help them to identify the parts. If you are going to allow them to use the instrument, please instruct them to be very careful with it as it is expensive and easily broken. | |
| 6. Read both thermometers to be sure they register the same temperature. | |
| 7. Wet the wick and place it on the bulb of one of the thermometers. | 7. Watch your teacher prepare the psychrometer for use |
| 8. Swing the psychrometer for about 30 seconds to allow maximum evaporative cooling. | 8. Time your teacher's swinging of the psychrometer. It should swing for about 30 seconds. |
| 9. Read the temperatures on the tow thermometers. | |
| 10 Record the temperatures on the chalkboard and have students subtract wet-bulb temperature from dry-bulb temperature to obtain the wet-bulb depression. | 10. Subtract the wet-bulb temperature from the dry-bulb temperature to obtain the wet bulb depression. |
| 11. Help students find the dewpoint temperature and relative humidity using the charts. | 11. Using the charts provided, find the dewpoint temperature and the relative humidity. |
CONCEPT OF ACTIVITY #2: Humidity can be measured with a sling psychrometer
SKILLS LEARNED:
Making observations, making measurements, recording data, organizing
data, making interpretations of data, using numbers, drawing conclusions.
TOPIC C: Water In the Air
ACTIVITY #3: Building Your Own Psychrometer
MATERIALS NEED PER STUDENT: 2 identical thermometers, white cotton shoelaces, cardboard (about 6" x 8"), marker, water, worksheet, glue, tape or stapler
DESCRIPTION: Students can each make their own psychrometer to take home or you may wish to make a set to keep in the classroom.
INSTRUCTIONS:
|
TEACHER |
STUDENT |
| 1. Have students glue dewpoint chart to the back of the cardboard. | 1. Glue dewpoint chart to the back of cardboard. |
| 2. Have students fasten the two thermometers side by side on the cardboard with tape, staples, or glue. | 2. Attach the two thermometers side by side on the cardboard with tape, staples, or glue. |
| 3. Have students label thermometers wet-bulb and dry-bulb. | 3. Label one thermometer wet-bulb and the other dry-bulb. |
| 4. Help students cut shoelaces into pieces about one inch in length and see that each student gets one. | 4. Cut a piece of shoelace about one inch long. |
| 5. Help students wet their shoelaces and slip onto the wet-bulb thermometers. | 5. Wet shoelace thoroughly and slip over bulb of the wet-bulb thermometer. |
| 6. Have students wave cardboard quickly back and forth to cool the wet-bulbs. | 6. Wave cardboard back and forth quickly to cool the wet-bulb. |
| 7. Using the chart you pasted on the back determine dewpoint as directed in Activity C-2. |
CONCEPT OF ACTIVITY #3: Humidity can be measured with a psychrometer.
SKILLS LEARNED:
Making measurements, using numbers.
TOPIC C: Water In the Air
ACTIVITY #4: Does Location Affect Dewpoint?
TYPE OF ACTIVITY: Small Group
MATERIALS NEED PER GROUP: psychrometer, worksheet #4 or can, ice, thermometer, water, worksheet #6, pencils
DESCRIPTION: Students will measure temperature and dewpoint at a variety of locations to see if surrounding have an effect on these measurements.
BACKGROUND INFORMATION FOR THE TEACHER: When making measurements of the atmosphere meteorologists are careful to always collect their data in the same manner each time. In this activity we will explore why they do this by observing how dewpoint and temperature can vary across even a small area. For this activity you will want to choose as many different locations you have time for. You may choose to have each group make only one or two measurements, but if time allows you may want to have each group do all of the measurements. Choose as many variations on location as you can (i.e., in the sun over pavement, in the shade over pavement in the sun over grass, in the shade over grass, under trees, away from trees, near an open source of water, away from water, etc.) This activity will proceed more smoothly if you allow the student to use psychrometers, but you may use the chilled mirror method (ice water and cans) if you prefer. You may create a temporary class set of psychrometers (see activity #c-3) using the student thermometers included in the kit as long as you don't cause permanent damage to the thermometers and you dismantle the psychrometers when you are done with them.
INSTRUCTIONS:
|
TEACHER |
STUDENTS |
| 1. Ask the student if they think they will measure the same dewpoint everywhere in the immediate area. | |
| 2. Before going outside help students compile a list of all the places where they would like to measure the dewpoint. Give each group their assignment. | 2. Compile a listing of the various places where you plan to make measurements of dewpoint. |
| 3. Take students outside and supervise the collection of data. | 3. Go outside and collect measurements for your group. Be sure to record both dry-bulb and wet-bulb temperatures if using a psychrometer. Record both air temperature and dewpoint if using a chilled mirror. |
| 4. Take students back to the classroom and help them determine dewpoints if needed. | 4. Return to the classroom. If psychrometers were used, determine the dewpoint for each location using the charts.5. Compile data and enter the results in chart on chalk board or overhead. Also make a personal copy. |
| 5. Help student compile all data and enter results in chart on chalk board or overhead. | |
| 6. Help students find pattern in the dewpoint variations. (Dewpoint should get higher in areas with more vegetation and near sources of water.) If you have no variation, look for reasons why. Are your grassy patches too small? Is it windy outside? (The wind can keep the air all stirred up eliminating variations.) | 6. Do you see any patterns in dewpoint from sun to shade? Trees to grass to pavement? Does the dewpoint vary with temperature? |
CONCEPT OF ACTIVITY #4: Location affects dewpoint.
SKILLS LEARNED:
Making observations, making comparisons, making measurements,
recording data, organizing data, making interpretations of data,
communicating findings, making inferences, using numbers, making
decisions, controlling variables, drawing conclusions, forming
generalizations, replicating procedures.
TOPIC C: Water in the Air
ACTIVITY #5: How Do Clouds Form?
TYPE OF ACTIVITY: Small Group
MATERIALS NEEDED PER GROUP: one gallon glass bottle, matches, water
DESCRIPTION: The process of cloud formation will be demonstrated in a glass bottle.
BACKGROUND INFORMATION FOR THE TEACHER: Clouds and fog form when the water molecules (vapor) floating in the air start ticking together to form tiny droplets of water about 20 micrometers (.002 centimeters or .0008 inches) in diameter. This process normally does not begin until the air is at or near saturation. On of these drops of water alone would obviously be too small to observe, but when large groups of them come together they are easily noticed as clouds or fog. Cloud droplets do not readily form on their own. They are generally helped along by the presence of condensation on the atmosphere. These nuclei are simply small bits of dust, salt, smoke, etc., that provide a favorable surface for condensation to occur. If the weather is cold enough students can easily duplicate the activity by simply breathing through their mouths when they go outside.
INSTRUCTIONS:
|
TEACHER |
STUDENTS |
| 1. Ask students if any of them have ever been inside of a cloud (fog is a cloud on the ground). Have them describe what it was like. | 1. Have you ever been inside of a cloud? Describe what It was like. |
| 2. Now ask them what they think they would have to do to form a cloud right now inside their classroom. Guide students to the idea that they must saturate the air either by lowering its temperature to the dewpoint or by adding more water vapor. | 2. What would you have to do to form a cloud inside of your classroom right now? |
| 3. Give each group a bottle. Ask them if they think it would be easier to make a could in it than in the room. Help them determine that their breath is an ideal source of water vapor and the bottle is a great place to capture it. | 3. Look at your bottle. Would it be easier to make a cloud in there? How would you do it? Do you have a convenient source of warm saturated air? |
| 4. Rinse the bottle out with a little water so that it's wet on the inside. With your mouth held tightly against the mouth of the bottle, breathe into it to increase the pressure and add more moisture. | |
| 5. When you take your mouth away form the bottle the air pressure will drop back down to room temperature and the air will cool down. you shouldn't, however, see a cloud in the bottle. Ask the students why no cloud appeared. (There were no condensation nuclei present.) | 5. Why didn't you have any luck creating a cloud? What was missing? |
| 6. Light a match and blow it out. Drop the blown out match into the bottle. Breath into the bottle again. Why was the cloud formation successful this time? |
CONCEPT OF ACTIVITY #5: Clouds form when water vapor condenses onto particles in the air called condensation nuclei.
SKILLS LEARNED:
Making observations, making comparisons, communicating findings,
making decisions, controlling variables, drawing conclusions.
TOPIC C: Water in the Air
ACTIVITY #6: Sky Cover and Cloud Types
TYPE OF ACTIVITY: Large Group
MATERIALS NEEDED: cloud poster, worksheet #7, cloud slides and script , slide projector
DESCRIPTION: Students will learn how to estimate cloud cover and determine cloud types.
BACKGROUND INFORMATION FOR THE TEACHER: Cloud identification takes practice. Encourage your student sot study the poster often and as a group try to check the sky daily. Use the following guidelines to determine sky cover:
| Clear | less than 10% covered by clouds |
| Partly Cloudy | between 10 and 50% cloud cover |
| Mostly Cloudy | between 50 and 90% cloud cover |
| Overcast | More than 90% cloud cover |
| Obscured | fog, rain, etc. blocking view of sky |
INSTRUCTIONS:
|
TEACHER |
STUDENTS |
| 1. Mount the cloud poser in a place where all student have access to it. | 1. Notice where your teacher has hung the cloud poster. Study it often. |
| 2. Give student copies of the cloud types chart. Encourage them to use this when outside identifying clouds. | 2. Keep the cloud chart your teacher gives you. It will help you when you go outside to study the clouds. |
| 3. Go through the slides with the class. Read the descriptions of the different cloud types as you go through the pictures. | 3. Follow along as your teacher describes the clouds. Make note of important characteristics and forecasting information. |
| 4. Take the class outside if possible. Look at the sky and determine what type (or types) of clouds are present. Be aware that there may be more than one layer of clouds in the sky, and each will be a different type. | 4. Determine what type (or types) of clouds are present in the sky. What type of weather is indicate |
| 5. After the class has determine what type of clouds are in the sky, have them determine the amount of cloud cover. | 5. Determine the degree of cloud cover. |
CONCEPT OF ACTIVITY #6: Clouds are organized into ten basic types.
SKILLS LEARNED:
Making observations, classifying objects, making comparisons,
communication of finding, making inferences, predicting outcomes,
drawing conclusions, forming generalizations.
TOPIC C: Water In the Air
ACTIVITY #7: Be a Rainmaker
TYPE OF ACTIVITY: Large Group
MATERIALS NEEDED: large beaker or Pyrex bowl, flat pan that will sit securely on beaker, water, ice, hot plate, water cycle poster
DESCRIPTION: Now that the students know how to make a cloud you can take it one step further and show them how those cloud drops form rain.
INSTRUCTIONS:
|
TEACHER |
STUDENTS |
| 1. Put 2-3 inches of water in beaker and place it on hot plate. While waiting for the water to boil have students predict what's going to happen to the water. Help them determine that the rising steam is a cloud. | 1. Deduce what will happen to the water as it heats up and watch to see if you are correct. |
| 2. Place the pan on top of the beaker and put enough ice in it to cover the bottom. | |
| 3. After a minute or so the water drops forming on the bottom of the pan will become so heavy that they fall off. | 3. Watch what happens to the steam when its upward movement is halted by the ice filled pan. |
| 4. Show the students the water cycle poster. Help them connect the hot plate with the sun's energy and the ice filled pan with the cold upper levels of the atmosphere. | 4. Look at the water cycle poster. Compare it to the demonstration you have just seen. |
CONCEPT OF ACTIVITY #7: When cloud droplets grow too heavy to float they fall to the ground as precipitation.
SKILLS LEARNED: Making observations, making comparisons, making inferences, communicating findings, predicting outcomes, drawing conclusions, forming generalizations.
TOPIC C: Water In the Air
ACTIVITY #8: How To Read a Rain Gauge
TYPE OF ACTIVITY: Individual
MATERIALS NEEDED PER STUDENT: worksheet #8, ruler, pencil, rain gauge, water
DESCRIPTION: Students will learn to use and read a rain gauge.
BACKGROUND INFORMATION FOR THE TEACHER: Rain gauges come in many sizes and shapes. If the opening at the top is the same size as the measuring chamber, the gradations for measuring rainfall depth are spaced their normal distances apart. Automated weather station relying on electronic equipment use tipping bucket rain gauges. The tipping bucket looks and acts like a seesaw. One bucket will collect rainfall until it's received a set amount (say .01 inches) at which time it drops down and empties. The second bucket will now collect rain until it becomes full and empties moving the first bucket back I place. Each time a bucket tips it flips a switch. A counter keeps track of how many times the bucket has tipped and therefore, how much rain has fallen.
When using a rain gauge it is important that you place it in an open location where I does not receive extra water (such as near a gutter) and it does not have any of the rainfall blocked (such as under a roof or near a tree). Be sure to place it in an open location. It is also important to empty it at the end of the measuring period. You may wish to do this once a day or every time you take a reading and record the amount.
INSTRUCTIONS:
|
TEACHER |
STUDENTS |
| 1. Pass out worksheets to the students. Draw a diagram of a rain gauge on the board. Point out the curved line indicating water level. This curved line is called a meniscus. It exists because of adhesion. Water molecules stick to the gauge better than they stick to each other (cohesion). | |
| 2. Explain to them that the water depth in a rain gauge (or any vessel) is measured by reading the bottom of the meniscus. | 2. Note the way the surface of the water curves down toward the center. This curved line is called a meniscus. |
| 3. Have them use their rulers to measure the water depths in each rain gauge on their worksheets. | 3. Using your ruler, measure the water depth in each of the gauges on your worksheet. |
| 4. You may also wish to put some water in the actual rain gauge and have students practice with reading it. | 4. If the teacher has put water in the actual rain gauge, practice reading the level in it. |
CONCEPT OF ACTIVITY #8: Rainfall is measured with a rain gauge.
SKILLS LEARNED:
Making observations, making measurements, using numbers.
TOPIC C: Water In the Air
ACTIVITY #9: Building Your Own Rain Gauge
TYPE OF ACTIVITY: Individual
MATERIALS NEEDED PER STUDENT: half-gallon milk carton, scissors, ruler, waterproof marker
DESCRIPTIONS: Students will construct their own functioning rain gauges from cardboard milk cartons.
INSTRUCTIONS:
|
TEACHER |
STUDENTS |
| 1. Give each student a milk carton and help them cut the top off so that they are each left with a box about 3-4 inches deep. | 1. Cut the top off of your milk carton so that you are left with a box about 3-4 inches deep. |
| 2. Have students cut one side out from the top of the carton. It should fit snugly into the box. | 2. Cut one side from the top half of the carton and check to see that it will fit snugly in one end of your box. |
| 3. Be sure the students mark their gauges form the bottom up. | 3. Pull this side piece back out of the box. Using a water proof marker and your ruler make a series of marks on this piece starting from the bottom that are 1/4 inch apart. Label the inch lines (an maybe the 1/2 inch lines) making sure you count up from the bottom. |
| 4. Have students put the marked gauge back into the carton. | 4. Put the side piece back in the box and set it outside on a level surface. |
| 5. They are now ready to put their rain gauges in an open location to measure the next rainfall. |
CONCEPTS OF ACTIVITY #9: Rainfall is measured by catching it in a rain gauge.
SKILLS LEARNED: Making measurements, recording data, using numbers