Heating Earth Surfaces

Transcription

1 Heating Earth Surfaces to minute sessions ACTIVITY OVERVIEW L A B O R ATO R Y Students design an experiment to measure how the Sun s energy heats land and water as well as how quickly both of those substances cool. An Anticipation Guide elicits students current ideas about the warmth of land and water and reinforces the idea that differences in heating and cooling of land and water are important factors in determining climate. KEY CONCEPTS AND PROCESS SKILLS (with correlation to NSE 5 8 Content Standards) 1. One way to gather data is through observations. Accurate and complete observations are important to making conclusions about the natural world. (Inquiry:1) 2. Scientist collect reproducible data, from which they can provide evidence for scientific ideas and explanations. (Inquiry: 1, 2) 3. The sun is the major source of energy for phenomena on the earth s surface, including ocean currents, winds, the water cycle, and other factors that influence weather and climate. (EarthSci: 3) 4. Factors that influence climate include the heating and cooling of land and water, ocean currents, latitude, elevation, landforms, and global wind currents. (Earth- Sci: 1) KEY VOCABULARY climate hypothesis energy E-53

2 Activity 55 Heating Earth Surfaces MATERIALS AND ADVANCE PREPARATION For the teacher * 1 transparency of Science Skills Student Sheet 5, Elements of Good Experimental Design * 1 overhead projector * 2 large basins or buckets 1 Scoring Guide: DESIGNING INVESTIGATIONS (DI) For each group of four students 2 white plastic trays 2 clear plastic films 2 plastic-backed thermometers 1 30-mL graduated cup 1 spoon 1 metric ruler * 1 watch with second hand * water sand * sunlight (or a light source, such as a 40W lamp, grow lamp, or flashlight) For each student 1 Student Sheet 55.1, Anticipation Guide: Heating Earth Surfaces * 1 sheet of graph paper 1 Student Sheet 55.2, Writing Frame: Investigating Earth Surfaces (optional) 1 Student Sheet 55.3, Sample Procedure (optional) 1 copy of Scoring Guide: DESIGNING INVESTIGATIONS (DI) (optional) *Not supplied in kit The day before conducting the activity, place the sand in an open container, such as a basin or a bucket, in a dry area to ensure that it is free of excess moisture. Also put a container of water out early enough before class that it will adjust to room temperature. In this activity, students are expected to design their own experiment. If you think they will have difficulty, you might provide optional Student Sheet 55.2, Writing Frame: Investigating Earth Surfaces, or Student Sheet 55.3, Sample Procedure, to help guide them. Ideally, this activity is conducted using direct sunlight either outside or on a windowsill during a bright, sunny day. Keep in mind the time of year that you are performing this activity. In the spring and fall, temperatures changes are clearer than in the winter when sunlight is often less intense. If you are conducting this activity in the winter, you may want to arrange to perform this lab during the time of day with the most intense sunlight to get the best results. E-54

3 Heating Earth Surfaces Activity 55 If the weather, your location, or the time of day the class meets prevents conducting this activity with direct sunlight, a 40W (or higher) lamp or a grow lamp will work instead. Gather enough light sources so that each group of four students will have one. If you cannot provide enough lamps, consider giving each group two flashlights, one for each tray being tested. Have students hold the flashlight 5 cm above the surface of the substance. To assist the student in keeping the flashlight steady, consider taping it to a meter stick and taping the meter stick to the wall. This will help keep the flashlight steady. Note: The temperature changes with flashlight heat will differ by about 3 C from the data described in the Teaching Suggestions. Masters for Scoring Guides are in Teacher Resources III: Assessment. Masters for Science Skills Student Sheet 5, Elements of Good Experimental Design are in Teacher Resources II: Diverse Learners. SAFETY If you are using lamps to heat the sand and water, the lamps may become very hot over the course of the experiment. Remind students not to touch hot lamps. TEACHING SUMMARY Getting Started 1. (LITERACY) Elicit student ideas about the heating and cooling of earth surfaces using Student Sheet Doing the Activity 2. (DI ASSESSMENT) Students design an experiment to determine how the sun s energy heats different earth surfaces and how they then cool. Follow-Up 3. The class discusses the results of the experiments. 4. (LITERACY) Students revisit their earlier ideas about the heating and cooling of land and water.if this works) E-55

4 Activity 55 Heating Earth Surfaces BACKGROUND INFORMATION Heating Earth Surfaces Several factors determine the earth s weather and climate. This investigation explores one such factor, the sun s energy and its interactions with land and water. Different areas of the earth are not the same temperature. This is because of the properties of substances. Two important properties are albedo, or reflectivity, and specific heat. The albedo refers to the percentage of the sun s radiation that is reflected off the surface of a substance. The specific heat of a substance describes how much energy a substance must absorb or release to obtain a given change in temperature. A substance with a higher specific heat will heat up and cool down at a slower rate than a substance with a lower specific heat. Specific heat is defined as the amount of energy needed to raise 1 gram of the substance 1 C. The amount of the sun s energy needed to raise the temperature of 1 gram of water is greater than the energy needed to raise the temperature of 1 gram of sand. This is because the specific heat of water (1 calorie per gram C ) is greater than the specific heat of quartz sand (0.19 calorie/gram C). Because of this, sand will heat and cool more quickly than water. In this way, earth surfaces which heat and cool at different rates, contribute to the development of varying weather and climate patterns. E-56

5 Heating Earth Surfaces Activity 55 TEACHING SUGGESTIONS GETTING STARTED 1. (LITERACY) Elicit student ideas about the heating of earth surfaces using Student Sheet Hand out Student Sheet 55.1, Anticipation Guide: Heating Earth Surfaces, which provides a preview of important ideas in the activity and elicits students thinking about these ideas. You may want to read the statements aloud and clarify any questions students might have about their meaning. Instruct each student to record whether he or she agrees or disagrees with each statement by placing a + or in the Before column. Explain that they will have a chance to revisit these statements after the activity to see if their ideas have changed or remained the same. DOING THE ACTIVITY 2. (DI ASSESSMENT) Students design an experiment to determine how the sun s energy heats different earth surfaces and how they then cool. Demonstrate how to use the equipment to measure the temperature of the substance in each of the trays. If necessary, provide some guidelines on how to conduct an accurate experiment. Students fill their trays one with sand and one with water and insert the thermometer bulb into the substance. It is important that the thermometer be inserted into the sand (or water) at one end of the tray and not simply rested on the surface of the sand. Students should then place the widest cardboard edge of the plastic film over the bulb to shield it from direct light, ensuring that the temperature measured is that of the substance. Students are expected to work with their group to design the experiment. You may want to brainstorm with the class the elements of good experimental design, write them down, and post them in the classroom while students work to design their own investigations. You could also use a transparency of Science Skills Student Sheet 5, Elements of Good Experimental Design, to review some key aspects of designing experiments. Instruct students to address each of the experimental design components mentioned in Procedure Step 1, page E-28. When designing their experiments, students should determine how much sand and water to use and how long to let the experiment run. Some of them might also want to modify other aspects of the experiment by insulating the base of the trays to reduce heat transfer or modifying the type of sand or water being tested to more accurately represent the land and water in your area. Encourage students to incorporate such aspects into their experimental design. Important aspects of the experimental design of this activity include: Each group of four students will be testing two substances, sand and water, in two separate trays. (Each pair can set up and monitor one tray.) A good design uses identical amounts of each substance (50 ml of each substance provides good results). The two trays should receive the same exposure to sunlight and shade. The trays should be placed the same distance from the source of light, preferably side by side. Students can place them together outside, along a windowsill, or an exact distance (5 10 cm) from a lamp. Students will need to include both a heating and a cooling phase of their experiment. They should chose an identical amount of time (e.g. 10 minutes) for both heating and cooling, but keep those times continuous (i.e. from 0 to 20 minutes). This will help them when graphing their data. With 10 minutes in the direct sunlight and 10 minutes in shade, results may be seen in as little as 20 minutes. Note that students are unlikely to see significant temperature changes in either heating or cooling in less than 10 minutes. Generally, the longer the substances are tested, the more significant the temperature change. If class time permits, 30 minutes (15 minutes heating and 15 minutes cooling) will produce better results than 20. E-57

6 Activity 55 Heating Earth Surfaces After approving students experimental design, allow them to conduct the experiment and record their results. Since the investigations designed by different groups will vary, their data may also vary. In general, results should show that sand gets hotter than water, and that sand also cools more quickly than water. Sample data is provided in the table below. You may assess students on their ability to design an investigation using the DESIGNING INVESTIGATIONS (DI) Scoring Guide. If you are planning to assess their work, be sure to review with them your expectations for a Level-3 response. You may tell them, for example, that you expect them to have a clearly stated purpose, a hypothesis, a reproducible experiment that keeps all variables the same (except the one being tested), a well-designed and completed data table, and a conclusion that summarizes the data, reflects on the purpose, and re-evaluates the hypothesis. A Level 3 response is shown on Student Sheet FOLLOW-UP 3. The class discusses the results of the experiments. Have students complete Analysis Questions 1 and 2 before beginning a class discussion. In Question 2, students are asked to calculate the change in heating and cooling temperatures for both the sand and the water. If necessary, direct students to make the calculation using the formula below. You might also remind them that a positive value indicates an increase in temperature, while a negative value indicates a decrease in temperature. Change in temperature = final temperature initial temperature You might make a transparency of a student graph or a transparency of the sample graph shown under Suggested Answer to Analysis Question 1 to review sample results. It is a good idea to make a line on the graph to clearly mark the time at which the trays were removed from direct sunlight or the lamp was turned off. Remind students of this division between the heating and cooling phases of the experiment. (Note: It is possible that temperatures rise slightly after the light source is removed because of a delay in the sensing ability of the ther- Sample Response to Student Sheet 55.2, Writing Frame: Investigating Earth Surfaces Purpose: To investigate how different earth surfaces are heated by the sun s energy and then cooled. Procedure: (See Student Sheet 55.3.) Hypothesis: Both sand and water will heat and cool the same. Data table: (See table at right.) Conclusion: We will compare the temperatures of the sand and water during heating and cooling. If there is any difference in temperatures,they are affected differently by the sun s energy. Investigating Earth Surfaces Time (min) Temperature of sand ( C) Temperature of water ( C) Heating Cooling E-58

7 Heating Earth Surfaces Activity 55 mometer). Use the sample graph to lead a discussion about what the students observed during the experiment and to analyze patterns and trends in the data. 4. (LITERACY) Students revisit their earlier ideas about the heating and cooling of land and water. After they finish the investigation and analysis, have students complete Student Sheet 55.1 by either agreeing or disagreeing with the statements in the After column. Students are then expected to explain how the activity gave them evidence to support or change their ideas. Be sure to discuss students responses and review the accuracy of each statement. A sample response is shown below. Help students understand how differences in the heating and cooling of land and water can affect weather and climate. Ask, Think of different earth surfaces. Based on this investigation, what can you conclude about how the sun heats earth surfaces? Different substances, such as sand and water, heat and cool at different rates. Ask, Consider how quickly each substance lost heat. Which do you think is better at retaining heat oceans or land masses? Oceans are a heat sink and tend to lose heat more slowly than land. Ask, Why then do you think the land often feels warmer (for example, when you are standing on a beach and step in the ocean/ lake/river on a hot day)? Because oceans also heat more slowly than the surrounding land. EXTENSION Students will design experiments to further investigate how different surfaces on earth are heated by the sun s energy and then cool. Encourage them to be creative in designing experiment that address questions they still have, or questions that arose after completing Activity 55. Final Responses to Student Sheet 55.1, Anticipation Guide: Heating Earth Surfaces + 1. The sun s energy can heat earth surfaces, even though it is millions of kilometers away. This statement can be supported by evidence from the activity if the activity was conducted using sunlight. If the activity was conducted using lamps, ask students to support the statement with evidence from their personal experience, such as walking on the hot sand of a beach or sitting on a metal chair on a sunny day. 2. The sun s energy heats both land and water to the same temperatures. Evidence from the activity should contradict this statement since the land (sand) should have became hotter than the water After being heated, land cools faster than water. This statement can be supported by evidence from the activity. For example, land (sand) cooled 11 C while the water cooled 4 C Differences in land and water affect weather and climate. This statement is referred to in the introductory text. E-59

8 Activity 55 Heating Earth Surfaces SUGGESTED ANSWERS TO QUESTIONS 1. a. Create a graph of the data you collected. Remember to label your axes, title your graph, and include a key. Students graphs will vary. A sample graph is shown below. b. Summarize the trends that you see in your graph. Both substances started at the same temperature. The sand became hotter than the water, reaching a temperature of 32 C compared to 28 C for the water. The sand also became cooler than the water, reaching a temperature of 21 C while the water cooled to 24 C. The sand both heated and cooled more quickly than the water, since it warmed 7 C while the water warmed 3 C and it cooled 11 C while the water cooled 4 C. Graph of Sample Results: Investigating Earth Surfaces Over Time Earth Substances KEY: Sand Water 2. Copy the table below. Calculate the changes in temperature for each substance you tested, and fill in the table. Students answers will vary. Changes in the heating of the substances are likely to be in the range of 3 12 C. Changes in the cooling of the substances are likely to be in the range of 2 12 C. A sample table is shown below. Sample Temperature Changes Tray containing Change in Temperature During Heating Change in Temperature During Cooling Sand 7 C 11 C Water 3 C 4 C 3. What can you conclude about how land and water heat up and cool down? Support your answer with evidence from this activity. Land and water heat and cool differently. In the investigation, the sand became hotter (heated more quickly) and cooler (cooled more quickly) than the water. The temperature of the sand went up 7 C and the temperature of the water only went up 3 C. The temperature of the sand cooled 11 C and the water only cooled 4 C Time (min) E-60

9 Name Date Anticipation Guide: Heating Earth Surfaces Before starting the activity, mark whether you agree (+) or disagree ( ) with each statement below. After completing the activity, mark whether you agree (+) or disagree ( ) with each statement below. Under each statement, explain how the activity gave evidence to support or change your ideas. Before After 1. The sun s energy can heat the earth s surfaces, even though it is millions of kilometers away. 2. The sun s energy heats both land and water to the same temperatures. 3. After being heated, land cools faster than water The Regents of the University of California 4. Differences in land and water affect weather and climate. Issues and Earth Science Student Sheet 55.1 E-61

10 Name Date Writing Frame: Investigating Earth Surfaces 1. The purpose of my investigation is to: 2. I will use the materials to investigate this purpose by (describe your planned procedure): 3. My hypothesis is that: 4. I will record my data in a data table. I will create my data table on the other side of this student sheet The Regents of the University of California 5. I will be able to use my data to reach a conclusion. Based on my results, I should be able to conclude: Issues and Earth Science Student Sheet 55.2 E-63

11 Name Date Sample Procedure 1. Measure and pour 50 ml of sand into one of the white plastic trays. Gently tap the tray on a table to flatten the surface of the sand. 2. Measure and pour 50 ml of water into the second white plastic tray. 3. Place a thermometer in each tray. Insert the thermometer bulb into the substance, and rest the other end of the thermometer on the edge of the tray. 4. Protect the thermometer bulb from direct light and insulate the substances by placing a clear plastic film on top of each tray. The widest part of the darkened edge should cover the thermometer bulb. 5. Create a data table for recording the temperature in each tray. You will read the temperature every two minutes for 20 minutes. 6. Record the initial temperature in each tray in your data table. 7. Place the trays the same distance from the light source. If you are outside, place the two trays side by side on a flat surface. 8. Begin timing. 9. Record the temperature of the substance in each tray once every two minutes for 10 minutes The Regents of the University of California 10. At exactly 10 minutes, record the temperature in each tray. Then remove the trays from direct light, either by placing the trays in the shade or turning off the light source. 11. Continue recording the temperature of both substances for 10 more minutes. Issues and Earth Science Student Sheet 55.3 E-65