Sample Lesson from Weatherwise

Transcription

1 Sample Lesson from Weatherwise How Do Clouds and Rain Form? Introduction In this lesson: Students investigate how clouds and rain form. In Part One they stimulate the formation of a cloud. In Part Two they simulate the water cycle. Specific Expectations This lesson gives students opportunities to: Explain the formation of clouds and the effects of different cloud formations on weather and climate (5s111) Describe the water cycle in terms of evaporation, condensation, and precipitation (5s112) Describe the ways in which energy from the sun affects weather conditions (5s114) Use appropriate vocabulary, including correct science and technology terminology, in describing their investigations and observations (5s120) Assessment Students' responses on Reproducible 4 should give you a clear idea of their understanding of the water cycle. (5s112) In addition, assess students' diagrams of how clouds are formed and correct use of science and technology terminology (i.e. Evaporates, condenses, water vapour, precipitation). (5s111, 5s114, 5s120) Ask students questions such as: How does a cloud form? (Water vapour rises, is cooled by this rising or by encountering cooler air, encounters dust particles, then condenses into rain droplets that form clouds.) Why do different types of clouds form at different altitudes? (Clouds form wherever warm moist air meets cooler air, so cloud formation depends on constantly varying air temperatures that also change with altitudes.) How do Earth and its atmosphere recycle water? (The water evaporates from Earth's surface, condenses, and falls back to Earth as rain or snow, and the cycle begins again.) (5s111, 5s112, 5s120)

2 Getting Organized Time required: Activate 5-10 minutes; Explore 20 minutes (part one), 20 minutes (part two) with a three-hour waiting period; Apply 5-10 minutes Advance Preparation: Part One - Cut the tops off the plastic bottles. You can use 2-L bottles if necessary. Have sponges and paper towels ready to wipe up spills. Part Two - Using a utility or an Exacto knife, cut a hole about 7 cm by 9 cm in the side of each plastic bottle. Cut the top off each milk carton, making the side 5-7 cm high; then cut this piece in half diagonally. Lesson Vocabulary Condense: to change from gas or vapour into a liquid. Evaporate: to change from liquid into a gas or vapour. Water vapour: water in its gaseous form. Content Background Although clouds have inspired poets from William Wordsworth to Joni Mitchell, they are made of quite humble ingredients: water and atmospheric dust. When molecules of water on Earth's surface are warmed by the sun's energy, they move more quickly. As the molecules dance, some leap up to join the gases in the air above the water. We say the water has evaporated because it has been transformed from the liquid phase into an invisible gas called water vapour. If the air that contains this vapour is warm, it rises and cools. Since cool air can't hold as much water vapour as warm air, some of the vapour condenses, or turns back into tiny droplets of liquid water or tiny ice crystals. These droplets or crystals, which form around microscopic particles in the air (mostly smoke, dust, or ocean salt), remain for a time suspended in the rising air as clouds. When the droplets or crystals have grown too large and too heavy to remain suspended in the cloud, they fall to Earth. If the snowflakes fall through air that is above the freezing point, they will melt and finish their journey as raindrops. If not, they will reach the ground as snow. Curiosity Place Cumulonimbus clouds are the giants of the sky. They can grow 18 km high - twice the height of Mount Everest - and can hold more than metric tons of water. Activate Describing Weather Begin by asking students to describe today's weather. If it is sunny outdoors, ask: Why would there be more clouds on a day when it is going to rain than on a day when no rain is expected? Encourage students to discuss their ideas about the function of clouds.

3 Have students read the opening paragraph on page 14 and discuss the question. Record their answers on chart paper. Considering ESL Learners Provide students with the following list of nouns and adjectives: cloud/cloudy, rain/rainy, fog/foggy, ice/icy. Ask students to think of a time when weather could be described using these words. Have them relate their description to a partner. Encourage a discussion of the formation of clouds, fog, and rain. If time allows, ask students to think of other nouns that can be turned into adjectives by adding y to the end; for example, water/watery, sun/sunny, snow/snowy. Preconceptions Because clouds are white and fluffy, students may think they are made of some material other than water. In this lesson, students discover that cloud formation and rain are part of the ongoing water cycle of evaporation, condensation, and precipitation. Explore Preparing for the Exploration Materials per Group: clear plastic 2-L bottle, scissors, plastic cup, hot water, shallow pan, ice, warm water Suggested Group Size: four Approximate Time: 20 minutes Classroom Management: Prepare class sets of Reproducible 4 on page 34. Safety: Remind students to be very careful and use caution when handling hot water. Exploration I: Make a cloud. 1. Students carefully pour a cupful of hot water into the bottle. Remind them to be careful with hot water. 2. Students then put ice in the shallow pan and cover the top of the bottle with the pan. 3. As students observe the inside of the bottle, they should find that a cloud forms inside the bottle and water condenses on the bottom of the pan. They should record their observations. 4. Students repeat the exploration putting warm water instead of ice in the pan. They may see less of a cloud in the bottle. There should be no condensation on the pan. Ask students: How does the exploration demonstrate what happens in the atmosphere? How does it work differently from the atmosphere?

4 Troubleshooting Be sure students use really hot water for Step 1, or the cloud won't form. Make sure students use lukewarm water for Step 4, otherwise the results won't differ from Step 3. Exploration Results Students place a shallow pan with ice cubes over a plastic bottle with hot water. They see that the hot water in the bottle evaporates and forms a cloud, changing the liquid into a gas. Interpret your results. The hot water evaporated. The lower temperature of the air made the vapour turn back into droplets of water, forming the cloud. When the water vapour hit the cold pan, it condensed into water, forming droplets. When it was hot, the water evaporated and liquid changed to gas. When it was cooled, the gas changed to liquid. Students could change the temperature of the water, the distance between the hot water and the pan, or the height of the bottle. Ask them to find the best water temperature for making a model of a cloud. Communicate your results. Encourage students to use the proper terms such as evaporation and condensation in their diagrams. Exploration Connection: Clouds Have students read the text and examine the diagram. Point out that although clouds cannot form without dust to condense on, they are predominantly water. Cirrus clouds are light and feathery. Stratus clouds are layered or spread out. Cumulus clouds are puffy and rounded. Have students use the diagram to try to identify the clouds they see outside. All middle and high clouds are formed of ice crystals. Depending on the temperature of the air, the crystals will either remain frozen and fall as snow, or melt and fall as rain. Helping the Struggling Learner To help students understand how the air can contain invisible water vapour, have them cover a clear glass of water with plastic wrap and put it in front of a window or under a lamp. Ask if they see any water vapour. After a few minutes, have them observe the glass again. They will see condensed water on the inside of the glass and on the plastic wrap. Ask students how the water droplets got there. Point out that water vapour that is already in the glass condenses on the sides.

5 Exploration II Preparing for the Exploration Materials per Group: milk carton, scissors, tape, 2-L plastic bottle, modeling clay, three small plastic cups, soil, hot water, four to six ice cubes, self-sealing bag Suggested Group Size: four Approximate Time: 20 minutes Classroom Management: Save the plastic bottles for use in Lesson 5. Safety: Remind students to be very careful and use caution when handling hot water. Exploration: Observe the water cycle. 1. Students tape the two halves of the milk carton together to form a boat-shaped container that will be their "cloud". Students should tape the open edges of the milk carton halves together, fitting the "cloud" to the hole in the bottle. 2. Once the cloud fits well in the hole in the bottle, students then remove the "cloud". 3. After steadying the bottle with clay, students set a cup of soil in the bottle. They place two cups of hot water near the uncapped end of the bottle. To prevent spills, make sure students don't fill either of the cups with too much water. 4. Students tape the cloud in place. They fill the bag with ice cubes and place it inside the cloud. Explain to the students that they are making a model of the water cycle. To help them understand, ask them what they think the cup of water represents (the oceans or other bodies of water); what the cup of soil represents (the land); and what the plastic bottle represents (the atmosphere). Students should observe water vapour condensing on the surface of the bottle, then infer that the water in the cup is evaporating. 5. Students place the experiment in the sun or under a lamp and observe what has happened after three hours have passed. Students should find that the water in the cup has evaporated and the soil is moist. Ask students: Why did you think you needed to use a lamp for sunlight? Why is this called the water cycle? Troubleshooting To prevent the cups from tipping over, have one student hold the bottle while another secures the milk carton. Exploration Results Students are making a model of the water cycle. When water vapour in the bottle meets

6 the cold "cloud," the water vapour condenses on the carton and rains into the soil. Eventually the water in the soil will evaporate and the cycle begins again. Interpret your results. The water evaporated and the soil became moist. There would be less (farther apart of move closer together) evaporation. There might be more condensation because water vapour couldn't escape from the bottle. As water evaporated from Earth's surface, it forms clouds, which return the water to Earth in the form of rain or snow. Communicate your results. Encourage students to share their diagrams with someone at home. Ask them to share any questions they were asked when they explained the water cycle. Apply Closer to Home: Fog Review with students the outcome of the Explorations. Have them complete the following sentences. "When liquid water is heated, it..." (evaporates and forms water vapour) "When water vapour floats up into the atmosphere, it..." (mixes with other gases) "When water vapour cools and comes into contact with particles of dust, it..." (condenses and form a cloud) Then look at the chart from Activate and let students revise or add to their ideas on the causes of condensation and evaporation. Have students read Closer to Home. Ask: How is fog like other types of clouds? The most common way fog forms is when air cools until condensation occurs. Also, if water vapour is added until the air is saturated, condensation occurs. The sun heats the air and evaporated the water droplets. The less direct rays of the sun aren't strong enough to burn off the fog in the winter. A response to this answer could be that the sun heats the air and evaporates the water droplets. Less direct rays of the sun are not strong enough to burn off the fog in the winter. This is a good time to distribute Reproducible 4 on page 34. Think! Water vapour rises until it hits cool air and condenses to form a cloud. If moist air reaches a very high altitude, high clouds will form. If moist air cools quickly before it goes very high, low clouds will form.

7 Extending Learning: Tracking Clouds Students can learn more about clouds by making a nephoscope, a device for tracking the direction of cloud movements. Materials: round mirror, cardboard, marker, direction-finding compass 1. Glue the mirror to the centre of the cardboard. 2. Label the edge of the mirror with the compass points. 3. Take the nephoscope outside to an open area. Place it on level ground. Determine which direction is north, then point your nephoscope north. 4. Look for clouds in the mirror. Choose one and make an X on the mirror to mark one spot on the cloud's leading edge. Follow that spot and mark Xs on the mirror as the reflection of the cloud moves across it. 5. Draw a line connecting the Xs. The line should point in the direction the cloud was moving. Integrating Science Art: Make a Mural Have the class create a mural of the water cycle. Students should show the water from Earth's surface (from bodies of water as well as from living things) evaporating and drifting through the air as water vapour; meeting cooler air and condensing as clouds; and falling as rain and snow back to Earth's surface. Have students label the stages in the cycle and draw arrows from one stage to the next. Math: Make a Rain Gauge Students can learn more about weather patterns in your area by measuring precipitation. Materials: clear plastic bottle, scissors, tape, ruler, marker, four bricks 1. Cut off the top of the bottle and put it aside. 2. Put a piece of tape along the side of the bottle. Start at the bottom and use the ruler and marker to draw lines at 1 cm intervals on the tape. Divide each centimeter into 10 equal parts and make a mark for each millimeter. 3. Put the top back on the bottle upside down (without the cap) to serve as a funnel. 4. Set up the bottle outdoors in an open area where it will not get runoff from buildings. Stack two bricks on each side of the bottle to keep it upright. 5. Every day at the same time, empty your rain gauge and record the rain level on a chart. 6. At the end of a month, make a graph showing daily amounts or precipitation. Compare your results with those of the local weather bureau.