Transcript
3.2 Investigate
What Factors Affect How Much Thermal Energy an Object or Substance Has? When you made observations of the hand warmer, you noticed that the temperature of the hand warmer changed. When you watched toast in the toaster, you observed that the heating elements warmed the toast. Each of these examples included a change in temperature. A change in temperature is an indication that heat has been transferred from one place to another. All objects have some amount of thermal energy. Hotter objects have more thermal energy than cooler ones. When you increase the temperature of an object, it has more thermal energy. If the object is warmer than its surroundings, it will transfer some of its thermal energy into the surroundings as heat. One example of this is the hand warmer after it has been activated. Why is thermal energy transferred? How is thermal energy related to heat and temperature? Is thermal energy a kind of kinetic energy, or is it potential energy? These are all good questions, and after you understand their answers, you will know how to put steps that use heat, fire, or even ice, into your Rube Goldberg machine. You will start answering these questions by investigating the thermal energy of a single substance—water. You will run an experiment to compare the amount of thermal energy in three beakers of water. When you analyze your results, you will be able to identify two factors that affect the water’s thermal energy.
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Each group in the class will do either Experiment 1 or Experiment 2. The groups doing Experiment 1 will investigate the effects of temperature on water’s thermal energy. The groups doing Experiment 2 will investigate the effects of the mass of the water on its thermal energy.
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Set Up Experiment 1 Procedure 1. Label the two large beakers as A and B. 2. Pour 400 mL of cold water into Beaker A. Pour 400 mL of warm water into Beaker B. 3. Feel the sides of each beaker. Record your observations on your Thermal Energy in Water page. 4. Predict what would happen if you put the same mass of ice into each beaker. Which beaker do you think would melt the ice faster? Why? Record your predictions on your Thermal Energy in Water page. Then discuss your answers with your group and take notes of any differing opinions.
Set Up Experiment 2 Procedure 1. Label the two large beakers as C and D. 2. Pour 400 mL of warm water into Beaker C. Pour 200 mL of warm water into Beaker D. 3. Feel the sides of each beaker. Record your observations on your Thermal Energy in Water page. 4. Predict what would happen if you put the same mass of ice into each beaker. What will happen to the temperature of the water in each beaker? Why? Record your prediction on your Thermal Energy in Water page. Then discuss your answers with your group, and take notes of any differing opinions.
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Run Experiment 1 and Experiment 2 Procedure 5. You will work with three bags of ice. Label two of the bags A and B or C and D. Use the balance to find the mass of each bag and record the data on your Thermal Energy in Water page. 6. Measure the initial temperature of the water in both beakers. 7. If the warm water is below 35°C, pour it out and get new warm water. Your warm water should be between 35°C and 45°C. Record the temperature and volume of the water in each beaker on your Thermal Energy in Water page (Time=0 min). Leave a thermometer in each beaker. 8. Leave the unlabeled bag of ice on the table as a control. At the same time, place Bag A (or C) into Beaker A (or C) and Bag B (or D) into Beaker B (or D). Use the straws to hold the ice beneath the surface of the water in both beakers. Record the time that the bags went into the beakers. 9. Measure and record the temperature of the water in each beaker after 5 min and 10 min. Measure to the nearest 0.5°C. Gently swirl the water for 15 s to mix it before measuring the temperature each time.
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10. After 15 min, remove the bags of ice from the beakers. Working quickly, measure and record the final temperature of the water in each beaker. 11. Working quickly, open Bag A (or C), pour the melted water into the graduated cylinder, and measure its volume. Be careful not to spill the water or let pieces of ice get into the graduated cylinder. Record the volume of water. Empty the graduated cylinder and repeat the process for Bag B (or D) and for the unlabeled bag.
Analyze Your Data 1. Begin your analysis by making a line graph of the temperatures you measured in the two beakers. s Label your graph clearly as “Experiment 1” or “Experiment 2.” s Label the horizontal axis “Time” and divide it into minutes. For each beaker, you should have four data points—0, 5, 10, and 15 min. s Label the vertical axis “Temperature” and use 10°C increments from 0°C to 50°C. s Use one colored pencil or marker for graphing the data from Beaker A (or C) and another color for the data from Beaker B (or D). s For each beaker, plot the four data points and draw a line to connect the points. Include a key so people reading the graph will know which color represents which beaker.
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2. Set up a bar graph showing the volume of the water recovered from the three bags of ice. s Use the same colors you used in your line graph for bags A, B, C, and D. s Use a regular pencil or pen for the data from the unlabeled bag. s Include a key that identifies the color used for each bag. Make the scale of your bar graph such that differences in your data are apparent. s Label the graph clearly as “Experiment 1” or “Experiment 2.” 3. Examine your data table and your graphs and answer these questions: s Which beaker had the larger temperature change? s Which ice bag had the largest volume of melted ice? Which had the least? s What trend, if any, do you see in your line graphs?
Reflect With your group, answer the questions. Be prepared to share the answers with the class. 1. What do you think caused the temperature of the water in each beaker to change? Why do you think the temperatures did not all change by the same amount? 2. Which ice bag had the largest volume of melted ice? Why? 3. Which ice bag had the least volume of melted ice? Why? 4. a) In Experiment 1, Beakers A and B had the same volume of water. However, the initial temperature of the water was different. How did this affect the volume of melted ice in each bag? Which do you think had more thermal energy before ice was added: the water in Beaker A or the water in Beaker B?
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b) In Experiment 2, the water in Beakers C and D had the same initial temperature, but Beaker C contained more water than Beaker D. How did this affect the volume of melted ice in each bag? Which do you think had more thermal energy before ice was added: the water in Beaker C or the water in Beaker D? 5. In both experiments, one bag was placed in 400 mL of warm water, and another was not in any water at all. Which bag had more melted ice in it? What does this tell you about the thermal energy of the warm water? 6. Experiment 1 only: Did the cold water in Beaker A have thermal energy? Why or why not? 7. At the end of your experiment, which beaker had water with more thermal energy? What evidence supports your answer? 8. There was less thermal energy in the water in each beaker at the end of the experiment than at the start of the experiment. Where did the thermal energy go? Use your data to support your answer. 9. In your experiment, what factor affected the decrease in thermal energy in the water in each beaker? How does this factor help determine the amount of thermal energy?
Communicate Your Results ÛiÃÌ}>ÌÊ Ý« Each group in your class completed one trial of Experiment 1 or Experiment 2. When you share your data with one another, you will be able to see if the trends in your data match the trends in the data of the other groups in your class. If the trends match, you can be more certain that you have identified the way temperature and mass affect thermal energy. Prepare a small poster of your results to share with the class. Label the poster clearly as “Experiment 1” or “Experiment 2.” This poster should include the following: s your line graph showing how the temperature of the water in the beakers changed during your experiment s your bar graph showing the volume of liquid water you measured in each bag
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s a claim about the factors that affect how much thermal energy is in water ◆
Use your answer to the last Reflect question to develop your claim.
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Your claim should be stated something like this: A factor that affects the amount of thermal energy in water is [your factor]. When [factor] is [larger/higher/smaller/lower], the water has [more/less] thermal energy.
s evidence to support your claim s a comparison of your results to your predictions, what you know now that you did not know before this experiment, and any new questions you may have As you look at other groups’ posters, focus on two things: s Notice the graphs on each of the posters. The measurements will not be exactly the same on all the posters, but the graphs should have similar shapes for each experiment. Notice if any of the graphs have different shapes from yours. s Read the claims on each poster. How well do they match one another? Notice whether any other group stated any of your claims better than you did. Notice if any group made claims different from yours. Examine the evidence each group used to support their claims. Make sure you agree with the claims and evidence used to support each.
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After you have had a chance to see the other posters, discuss the answers to the Reflect questions as a class. Make sure you understand the answers to each of the questions. When you get to the last question, develop a set of class claims about the factors that determine the amount of thermal energy an object possesses. Choose one or two sets of data from the posters to support those claims.
What Factors Affect How Much Thermal Energy an Object or Substance Has? One factor that affects how much thermal energy a substance has is temperature. Experiment 1 provided evidence of the effect of this factor. In Experiment 1, you observed that more ice melted in the warm water in Beaker A than in the cold water in Beaker B. The temperature of the warm water in Beaker A was higher than the temperature of the cold water in Beaker B. Therefore, Beaker A had more thermal energy than Beaker B. When two substances of equal mass have different temperatures, the substance with the higher temperature has more thermal energy. Experiment 1 also showed you that even though the water in Beaker B was cold, it still had thermal energy. You know that because even though the water was cold, some of the ice that was placed into the beaker melted. Another factor that affects how much thermal energy a substance has is its mass. Mass is a measure of how much of something there is. Experiment 2 provided evidence of the effect of this factor. In Experiment 2, the water in both beakers was the same temperature. However, there was more water in one beaker than the other, and this made a difference. More ice melted in the water in the beaker with the greater mass of warm water than in the beaker with less water. The greater the mass of a substance of a given temperature, the more thermal energy it has. Based on these results, you can clearly support claims about two factors that affect the amount of thermal energy an object or substance has—temperature and mass. The claims can be stated as follows:
s A factor that affects the amount of thermal energy in an object or substance is temperature. When temperature is higher, the object or substance has more thermal energy.
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s A factor that affects the amount of thermal energy in an object or substance is mass. When the mass of an object or substance is greater (there is more of it), it has more thermal energy. You also experienced one more factor that affects the amount of thermal energy in a substance. In Experiment 1, more ice in the bag of ice submerged in the cold water melted than in the bag of ice left on the table. Although the cold water was colder (had a lower temperature) than the air around the ice on the table, the ice in the cold water was able to absorb more thermal energy than the ice left on the table. How could this have happened? You will be able to answer this question after you read about how thermal energy raises temperatures in Section 3.4.
Reflect 1. Revise your Energy Types page. If you did not have thermal energy on your page before, add it now. Record indicators and factors that affect how much thermal energy an object or substance has. 2. What else do you still need to know about thermal energy in order to use thermal energy in the Rube Goldberg machine you are designing?
What’s the Point? Two factors that affect thermal energy are temperature and mass. The greater each factor, the greater the thermal energy a substance has. In the first experiment, the water in Beaker A was at a higher temperature than the water in Beaker B. You know that Beaker A had more thermal energy because it melted more ice. In the second experiment, the water in Beaker C and Beaker D both began at the same temperature. However, because there was more water in Beaker C, it had more thermal energy. The water in Beaker C melted more ice than the water in Beaker D.
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