Why Are Temperatures Different Near the Coasts and Inland?

Transcription

1 2.6 Investigate Why Are Temperatures Different Near the Coasts and Inland? Earlier in this Learning Set, you analyzed climate maps that indicated the effects of latitude on temperature. The maps are repeated below. Those maps show bands across the United States that have similar average temperatures. But some places do not fit in with this pattern. You may have noticed that in the winter, places close to the coasts are much warmer than places at the same latitude farther inland. In summer, the opposite happens. A) Rapid City, South Dakota B) Burlington, Vermont C) Atlanta, Georgia D) Las Vegas, Nevada E) Minneapolis, Minnesota F) Dallas, Texas WW 110

2 2.6 Investigate Latitude affects temperature, but something else seems to be affecting temperature as well. Have you ever walked barefoot in the sand on a hot day? The sand can get so hot that you run into the water to cool your feet off. The same thing happens when you walk in bare feet on a hot blacktop street or driveway. All you want to do is run for the grass. Maybe you have wondered why the water or the grass feels cooler than the sand or the blacktop. If you know why, you will be able to explain why temperatures are different near the coasts than farther inland. Investigate Heating and Cooling of Land and Water In this investigation, you will simulate heating and cooling of land and water. You will use sand to model land, and you will use water as water. You will use a bright light bulb to model the solar energy. Your investigation will help you answer two questions: How does the heating of land and water differ? How does the cooling of land and water differ? Before running the experiments, you will make some predictions. Predict Predictions are sometimes written as If then statements. Complete these If then statements. If a sample of sand and a sample of water (with equal masses) receive the same amount of incoming heat energy, then the sand will heat up (faster or more slowly) than the water. If the source of energy is removed, then the sample of sand will cool (faster or more slowly) than the sample of water. Record your predictions on the Land & Water Temperature Data page. The light bulb can get very hot. Do not touch the bulb. Never look directly into the light bulb. Materials lamp with 250-W heat lamp bulb stand and clamp 2 clear plastic cups 2 plastic lids with holes in center 2 black paper liners for lids cup stand (optional) 200 g fine, dry sand 200 g water 2 thermometers tape or modeling clay clock with second hand scale for measuring sand and water ruler WW 111 WEATHER WATCH

3 Procedure 1. Label one cup water and one cup sand. Measure and carefully pour 200 g of water into one cup. Measure and place 200 g of sand into the second cup. 2. Place a lid with a black liner on each cup. 3. Carefully push a thermometer through the hole in each lid. The bulb of the thermometer should be placed so that it is just covered by the sand or the water. Secure the thermometer in place with tape or modeling clay. 4. Place the cups next to each other. Clamp the lamp so the light is about 30 cm above the top of the cups. Adjust the stand to position the light as shown in the picture. Use tape to fix the thermometers to the lamp as shown. 5. Use the Land & Water Temperature Data page to record data during this investigation. 6. Record the temperature in each cup. 7. Turn on the lamp and record the temperature in each cup every 3 min for 12 min total. Use extreme caution with the light bulb as it can get very hot. Do not look directly at the light bulb at any time. 8. Turn the lamp off and record the temperature in each cup every 3 min for another 12 min as the cups cool. 9. Return all equipment to its proper place and clean up your work area. WW 112

4 2.6 Investigate Analyze Your Data 1. Draw a graph to show how the two materials heated and cooled. Plot time along the x-axis. Plot the temperature in half-degrees along the y-axis. 2. What trends do you see on the graph? a) What differences do you see in how much the sand and water heated up? b) What differences do you see in the time it took for the sand and water to heat up? c) What differences do you see in how much the sand and water cooled off? d) What differences do you see in the time it took the sand and water to cool down? 3. Write a statement comparing the heating and cooling of sand and water. 4. Compare the results of your investigation with the prediction you made. Describe how the results are the same or different from your prediction. Communicate Investigation Expo Your group will share the results and analysis of your investigation with other groups in an Investigation Expo. You will need to make a poster to display your investigation results and some of your answers from your Analyze Your Data questions. On the top third of your poster, draw a diagram of your experimental setup. List the independent variable, dependent variable, and controlled variable. Remember that the independent, or manipulated, variable is the one you WW 113 WEATHER WATCH

5 intended to vary in the experiment. The dependent, or responding, variables are the ones that changed as a result of the procedure you are carrying out. They are the ones you measured. The controlled variables are the ones you make sure remain the same each time you carry out the procedure. In the middle third, present the graphs of your data. In the bottom third, summarize your results and decide how they may be applied to predicting temperatures near bodies of water. Once all groups have completed their posters, display all of the posters in the classroom. Walk around the room with your group looking at the graphs and information in the posters. Examine each group s prediction and notice whether it is different from your group s prediction. Examine the conclusions and compare them to your conclusions. Discuss any differences with your group. After everyone has examined each of the posters, review and discuss the answers to the Analyze Your Data questions. Refer to the posters during your discussions. Also, discuss possible reasons why any data might have differed from one group to another. Then, as a class, answer these questions: 1. Develop a statement or set of statements to answer the following: Based on your data, which heats up more quickly during the day land or water? Which cools more quickly at night land or water? 2. What do you think might cause land and water to heat and cool differently? 3. How do you think the heating and cooling of land and water affects the air temperature near the land and water? Use what you know about conduction to answer this question. WW 114

6 2.6 Investigate Why Do Substances Warm Up and Cool Off at Different Rates? Consider what you have just learned about the differences in the way sand and water heat and cool as you think about this question: Do all parts of Earth absorb incoming solar energy equally? The evidence from your investigation shows that the answer is no. You observed in your investigation that sand heated more quickly than water. This is because the sand absorbed more energy than the water. The same thing happens when land and water are heated by solar energy. Land areas absorb more solar energy and heat up faster than bodies of water. There are two reasons why land and water heat at different rates. Each absorbs and transfers energy differently, and each reflects light differently. Energy Transfer Why did the sand heat up faster than the water? One reason is that the amount of energy needed to increase the temperature of a substance differs from substance to substance. Scientists compare the way different substances heat up. They measure the amount of heat energy it takes to raise 1 g (gram) of a substance 1 C (degree Celsius). This is called the specific heat capacity (or specific heat) of a substance. The specific heat capacity of water is much higher than that of most other materials. Compared to other materials, a huge amount of energy is needed to raise the temperature of water. If you have ever waited a long time for a pot of water to boil you already know it takes a lot of energy to raise the temperature of water. Energy is measured in joules, and it takes about 4.2 J (joules) of energy to raise the temperature of 1 g of water by 1 C. But it takes only about 20 percent of that amount of energy (0.8 J) to raise the temperature of 1 g of dry sand the same amount. This is why it took longer for the temperature of the water to increase in your investigation than it did for the temperature of the sand to increase. Because less energy is needed to heat sand than water, the temperature of sand increases faster than that of water when the same amount of energy is added. That is why sand feels hotter to your feet than water on a hot day. specific heat capacity: the amount of heat energy required to raise the temperature of 1 gram of a substance by 1 Celsius. Which will heat up faster, the water or the sand in this coastal area? WW 115 WEATHER WATCH

7 Think about a hot day at the beach. After it gets dark, the sand does not stay warm for very long. This is because sand has a low specific heat capacity. When the air is cooler than the sand, the sand cools quickly as energy is transferred by conduction into the atmosphere. Water has to transfer far more of its energy into the atmosphere to cool by an equal amount. When a small amount of sand, 1 g, decreases by 1 C, the energy given off is 0.8 J. When the temperature of 1 g of water decreases by 1 C, the energy given off is 4.2 J. The specific heat capacity of water is much higher than that of sand. Reflect Refer back to the maps of January and July average United States temperatures at the start of this section and answer the questions below. 1. Why is the air over land warmer during the day than air over water? 2. Your friends moved from Gainesville, Florida to Tucson, Arizona, near the Sonoran Desert. They told you that summer days are much hotter in Tucson than in Gainesville. You notice that Tucson is at a higher latitude than Gainesville. How do you think different heating of water and sandy soil cause the temperature difference? 3. Your friends also observed that the difference between daytime temperature and nighttime temperature is much greater in Tucson, Arizona than in Gainesville, Florida. What reasons would you give to your friends for the greater temperature change in Arizona? reflect: to bounce back off a surface. 4. In winter, the average temperatures in the United States are much lower than the summer temperatures. What part of the country has the greatest change in temperature between July and January? Why do you think the temperature change there is much greater than the temperature change at other areas with the same latitude? Reflected Light Think about a fresh winter snow or a white sandy beach. The glare from the snow or white sand can be so bright that you squint or need sunglasses to see. This is because the snow and white sand reflect a high percentage of sunlight that strikes the surface. To refl ect means to bounce back off a surface. This means that snow or white sand absorb only a small amount of WW 116

8 2.6 Investigate light. If you have ever had the chance to walk on a white-quartz sand beach in your bare feet, you know that even on a very hot day the sand feels comfortable on your feet. A substance absorbs some light and refl ects some light. Because different materials reflect different amounts of incoming light, they also absorb different amounts of light. You discovered in this section that the specific heat of a substance affects how quickly different substances heat and cool. The amount of light refl ected and absorbed by a surface also affects how quickly a substance gets warmer or cools down. Light-colored surfaces (like snow and white sand) refl ect more light than dark-colored surfaces (like a blacktop road). The amount of light reflected by water can vary a lot, from 8 percent to as much as 98 percent, depending on how the sunlight strikes it. Overall, Earth reflects about 30 percent of the light that shines on it, so it absorbs about 70 percent. The table shows the percentage of light reflected by some common materials. Surface snow, fresh 80%-90% Percentage of light energy reflected Looking at freshly fallen snow can make you squint, even on a cloudy day. Snow reflects 80 percent to 90 percent of the sunlight that strikes it. This means that snow only absorbs 10 to 20 percent of that light. cloud, average 50%-55% snow, old 45%-70% white sand 30%-60% concrete 17%-27% green crops and grass 5%-25% soil, dark 5%-15% water 8%-98% blacktop road 5%-10% WW 117 WEATHER WATCH

9 Reflect 1. Why do people who want to stay cool on a hot summer day wear white clothing? 2. What Earth surfaces do you suppose reflect the greatest amount of solar energy? What Earth surfaces do you suppose absorb the greatest amount of solar energy? 3. Why does sand heat faster than water? Give two reasons. Which reason do you think has the greater effect? Why? 4. Why does a blacktop driveway or street heat faster than the grass? Give two reasons. 5. Why do you think the air above a blacktop driveway or street is warmer than the air above a white sidewalk? Explain Now that you know that energy is absorbed differently by different substances and that different substances reflect light differently, you probably have some ideas about why temperatures are different near the coasts and inland. It is time to work with your group to explain why. You may not be fully satisfied with your explanation, but do your best based on what you know. After you know more, you will have a chance to revise your explanation. WW 118

10 2.6 Investigate Use a Create Your Explanation page, and begin by recording the question you will answer: Why are temperatures different near the coasts and inland? Then work with your group to develop a claim that answers the question. Your claim can be simple and it can include the different substances found at the coasts. It does not have to include what you know about how those materials affect the air temperature. You may save that information for the explanation statement. Your evidence can come from the investigation you did earlier in this section. The science knowledge that will go into your explanation should come from the reading you just did. Make sure to include what you know about the specific heat capacity and percentage of light reflected by different substances and also what you know about how air temperature is affected by surface temperature. Then, develop an explanation statement that answers the question and convinces someone that your answer is trustworthy. Your explanation statement should provide what you know about what causes the air to be different near the coasts and farther inland. As you develop your explanation statement, you may find that you do not know everything you need to know to explain why air temperatures are different at the coasts. Identify what else you need to learn to develop a complete explanation, and be prepared to share what you still need to learn with the class. Communicate Share Your Explanation When it is your group s turn, share your explanation with the class. Then tell them what else you need to know to make your explanation better. Revise Your Explanation As a class, select or create an explanation to answer this section s question: Why are temperatures different near the coasts and inland? Use scientific terms in your claims and explanation statements. Decide together what else you need to learn to better answer the question. WW 119 WEATHER WATCH

11 The high specific heat capacity of water means that oceans store much of Earth s thermal energy. Temperatures at the Coast Water has a higher specific heat capacity than most materials. This means that water needs to absorb a lot of energy to heat up. Water also needs to transfer a lot of energy to cool down. As a result, water takes longer to heat and longer to cool than most other materials. Depending on conditions, water can also reflect much more light than land. Reflection of light is a second reason why water can take longer to heat up than other materials. Most of the energy from sunlight passes through the atmosphere without causing molecules to move faster. The sunlight is absorbed or reflected when it reaches Earth s surface. This means Earth s atmosphere is heated mostly by conduction and radiation from the warm surface beneath it. As you saw in the model, the materials that make up land heat up quickly and release energy quickly, because they do not have a high specific heat capacity. The air above land tends to warm rapidly after the Sun rises in the morning. Because land does not store heat well, it tends to cool down quickly after the Sun sets. As a result, the air above land tends to cool rapidly after the Sun sets. When sunlight strikes water, the water (with its high specific heat capacity) warms up more slowly than the nearby land. That means that the air above the water also heats up slowly after the Sun rises. Water needs to transfer a lot of energy to cool down, so it cools off slowly after the Sun sets. For this reason, at night the air above water cools off more slowly than the air above nearby land. Because land heats faster than water after the Sun rises, the air above land is warmer than air above water early in the day. And because land cools faster than water after the Sun sets, the air above water is warmer than air above land during the night. The high specific heat capacity of water is important for weather and climate. Because so much of Earth s surface is covered by water, oceans are able to store huge amounts of energy. Even when the water feels cool to you, it is storing a lot of energy. The transfer of energy between oceans and the atmosphere above them is one of the major factors in determining weather and climate around the world. WW 120

12 2.6 Investigate Reflect 1. You take a canoe out on the water at 10 A.M. on a bright, sunny day. Before leaving the sandy shore, you measure the air temperature and find that it is 75 F. You measure the temperature again when you are about 500 m from shore. How do you think the second reading will compare to the first? Why? 2. At sunset, you paddle your canoe from the middle of the lake to the sandy shore. When you left, the temperature in the middle of the lake, was 65 F. You take another reading when you reach the shore. How do you think these temperature readings will compare to each other? Why? 3. How do you think shore and offshore temperature readings taken at 2 P.M. will compare with each other? Why? Revise Your Explanation Earlier, you developed an explanation of why temperatures are different along the coast than farther inland. Now you have communicated with your class and read more about the effects of land and water on temperature. Revise your explanation to include any new information you have. Begin with your claim. Do you need to make it more accurate? Can you state it better? Then look at your evidence and science knowledge. Think about what you can add to them. Make sure your claim, evidence, and science knowledge are consistent with each other. Then look at your explanation statement. Perhaps you can make it more accurate. Include the new science knowledge you recorded. Make sure your explanation statement is consistent with your claim, evidence, and science knowledge. Communicate Share Your Explanation When it is your group s turn, share your explanation with the class, and tell them what else you think you need to know to make your explanation better. Revise Your Explanation As a class, select or create an explanation to answer this section s question: Why are temperatures different near the coasts and inland? Use scientific terms in your claims and explanation statements. WW 121 WEATHER WATCH

13 Then work together as a class to answer this Learning Set s question: Why are there differences in temperature? Update the Project Board Since the last time you updated the Project Board, you have explored the reasons why temperatures are different near the coasts and farther inland. You have also brought together what you have learned in all the sections to answer the Learning Set s question: Why Are There Differences in Temperature? Record what you have learned in the What are we learning? column, and include evidence for your entries in that column to the What is our evidence? column. Examine the questions in the What do we need to investigate? column. If you know the answers that are not already recorded in the What are we learning? column, record those answers and your evidence. If you have more questions, add them to the What do we need to investigate? column. Remember to update your personal Project Board as the class Project Board is updated. What s the Point? Specific heat capacity is a measure of how much heat energy it takes to raise the temperature of 1 g of a substance by 1 C. Water warms up and cools down more slowly than an equal mass of sand, because it has a higher specific heat capacity than sand. Water has a higher specific heat capacity than most materials. Water also refl ects much of the light that strikes it. As a result, it takes a lot of energy to heat water, and water has to release a lot of energy to cool. Therefore, water tends to heat and cool more slowly than most other materials. Most sunlight passes through Earth s atmosphere without being reflected or absorbed. This means Earth s atmosphere is heated mostly by conduction and radiation from the warm surface beneath it. Land heats up faster than water after the Sun rises, so early in the day air above the land will be warmer than air above the water. At night, the land cools off faster than the water, so at night, air above land will be cooler than air above the water. The transfer of energy between Earth s vast oceans and the atmosphere above them is one of the major factors that infl uences weather and climate around the world. WW 122