Begin the analysis with a discussion of the concepts introduced during the lab. Ask students the following questions to initiate a discussion of these concepts.

Ask students: What is a pulley? It’s a simple machine.

Ask students: Did you notice a difference when you lifted the load with the pulley as compared without the pulley? Student answers may vary. It is likely students will indicate that the load didn’t feel as hard to lift when they used the pulley.

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Students should refer to the calculations for work they recorded in Problems 3 and 4 in their Student Data Record. Review the results from Trials 1 and 2:

Ask students: Even though the load felt easier to lift with the pulley, was there a difference in the force exerted to lift the load? Was there a difference in the work done to lift the load? Students should observe that the force and work done were the same when the load was lifted without and with the pulley.

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Students should refer to the calculations for work they recorded in Problems 5 in their Student Data Record. Review the results from Trials 3 and 4:

In Trials 3 and 4, students kept the distance the same as in Trials 1 and 2 (20 cm), but changed the load (from 200 g to 150 g).

Ask students: Did you observe the same results in Trials 3 and 4 as in Trials 1 and 2? Was there a difference in how much force you applied to lift the load with or without the pulley, compared to Trials 1 and 2? 

Was there a difference in how much work was done to lift the load with or without using the pulley?

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Students should refer to the calculations for work they recorded in Problems 6 in their Student Data Record. Review the results from Trials 5 and 6:

In Trials 5 and 6, students kept the mass the same as in Trials 1 and 2 (200 g), but changed the distance (from 20 cm to 40 cm).

Ask students: Did you observe the same results in Trials 3 and 4 as in Trials 1 and 2? Was there a difference in how much force you applied to lift the load with or without the pulley, compared to Trials 1 and 2? 

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Calculate work for each of the 6 Trials in this Investigation:

Divide students into cooperative groups and encourage each group to use the data from Trials 3 through 6 to calculate work.

• A structured format for students to calculate the work done in each trial is provided for students in Problems 7 and 8 of their Student Data Records.
• If students have difficulty with the process or calculations, the calculations can also be completed as a class activity.

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The Cognitive Tool Summarize is used in this slide to organize and analyze student data. Isn’t it easier to look at this one Data Table to summarize and interpret your experimental results compared to flipping from page to page in your Student Date Record?

Once students focus on the data presented in this slide as sample data not unlike their own data, begin to analyze the Data Table with them. 

Ask students the following questions and refer to the data in this slide as you discuss their responses.

You performed three sets of experiments. Can you describe the three different sets? Trials 1 and 2 represent one set, Trials 3 and 4, represent a second set, and Trials 5 and 6 represent a third set. In the first set, Trials 1 and 2, the same load was lifted 20 cm. In the second set, Trials 3 and 4, a load with a lower mass was lifted 20 cm. In the third set, Trials 5 and 6, a load with the same mass as Trials 1 and 2 was lifted 40 cm.

Instruct students to denote the three sets on their Scientist Data Record by placing a bracket around the trials in each set. What was similar about each set? Students should relate that in each set the force exerted to lift the load, the distance the load was lifted, and the work done to lift the load were the same when the load was lifted without the pulley and with the pulley.

What was different between each set of trials? The amount of work done in each set was different from the work done in the other two sets.

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Ask students: Help students answer this question by walking them through one comparison.

Direct students to compare Set A (Trials 1 and 2) to Set B (Trials 3 and 4). Do you remember which variable you altered between the sets? Students may need a prompt to search for the differences in the Scientist Data Record, such as the contents of the buckets or the column labeled “Mass of the Load.” Students changed the mass of the load and therefore the force exerted to lift the load. The bucket in Trial 1 contained ten 1-gram cubes, one metal cube, three large bears, three medium bears, three small bears, and the paper clip and string. This was approximately 200 g. The bucket in Trial 3 contained ten 1-gram cubes, one metal cube, three medium bears, and the paper clip and string.

Look at Trial 1 and Trial 3. Did changing the mass of the load have an effect on the amount of force you exerted to lift the load without the pulley? Yes. When the 200 g load in Trial 1 was lifted 0.2 m, the force exerted to lift the load was 2.0 N. When the 150 g load in Trial 3 was lifted 0.2 m, the force exerted to lift the load was 1.5 N.

Did changing the mass of the load change the amount of work done in Trial 1 versus Trial 3? Yes. When the 200 g load in Trial 1 was lifted 0.2 m, the amount of work done to lift the load was 0.4 J. When the 150 g load in Trial 3 was lifted 0.2 m, the amount of work done to lift the load was 0.3 J.

Did changing the mass of the load have an effect on the amount of force you exerted to lift the load in Trial 2 versus Trial 4, the trials in which you used the pulley? Yes. When the 200 g load in Trial 2 was lifted 0.2 m, the force exerted to lift the load was 2.0 N. When the 150 g load in Trial 4 was lifted 0.2 m, the force exerted to lift the load was 1.5 N.

Did changing the mass of the load have an effect on the amount of work done in Trial 2 versus Trial 4? Yes. When the 200 g load in Trial 2 was lifted 0.2 m, the amount of work done was 0.4 J. When the 150 g load in Trial 4 was lifted 0.2 m, the amount of work done was 0.3 J.

When the mass of the load was changed, was there any difference between the force exerted or the amount of work done with or without the pulley within each set? No. Although less work was exerted in Trials 3 and 4 as compared to Trials 1 and 2, the work done with and without the pulley in each set was the same.

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The next part of the analysis may be conducted by students independently or structured as a class discussion.

If students are to work independently, assemble them into pairs or groups.

• Suggest that students follow a similar thought process to analyze the differences between Set A (Trials 1 and 2) and Set C (Trials 5 and 6). The questions that follow can be used to help students work through the comparisons.

Ask Students: Did changing the distance the load was moved or lifted, have an effect on the amount of work done in Trial 1 versus Trial 5, the trials in which you did not use a pulley? Yes. When the 200 g load in Trial 1 was lifted 0.2 m, the amount of work done was 0.4 J. When the same load in Trial 5 was lifted 0.4 m, the amount of work done was 0.8 J.

Ask Students: Did changing the distance the load was moved or lifted, have an effect on the amount of work done in Trial 2 versus Trial 6, the trials in which you used a pulley? Yes. When the 200 g load in Trial 1 was lifted 0.2 m, the amount of work done was 0.4 J. When the same load in Trial 6 was lifted 0.4 m, the amount of work done was 0.8 J.

Ask Students: When the distance the load was lifted changed, was there any difference= between the force exerted and the amount of work done within each set? No. Although more work was done in Trials 5 and 6 as compared to Trials 1 and 2, the work done with and without the pulley was the same in each set.

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Conclude the analysis by encouraging students to summarize how using the pulley relates to work. Utilize the questions and steps that follow:

Ask Students: Did the amount of force you exerted to lift a load change when you used the pulley as compared to without the pulley? No. The force was the same.

Ask Students: Did the amount of work done to lift the load change when you used the pulley as compared to without the pulley? No. The work was the same.

Ask Students: Did anything change between when you didn’t use the pulley and when you did use the pulley? Yes. When the pulley was used to lift a load, it felt easier than lifting the load without the pulley.

Ask Students: Why do you think the load felt easier to lift with the pulley? What is the advantage of the pulley? Student answers may vary, but guide students to the understanding that the force of gravity is present when they are lifting the load both with and without the pulley. However, when they pull the load upward, the direction of their applied force is in the opposing direction of gravity. Whereas, when they apply a force in a downward direction on the effort arm of the pulley, the force is in the same direction as the force of gravity. This makes the work feel easier. The advantage of using a pulley is that the applied force is in the direction of gravity.

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Ask Students: Why does work feel easier when using the pulley? Using a pulley does not reduce the force exerted to lift a load or the amount of work done to lift the load. However, a load often feels easier to lift with the pulley because the effort is applied in the same direction as the force of gravity. This is the advantage of using the pulley to do work.

Ask Students: Ask students to think about the situation with Cindy and her turkey that they had discussed earlier in the investigation. Could Cindy have used a pulley in her kitchen to help her when she lifted the turkey out of the oven? Yes. The pulley would not change the work Cindy would need to do to lift the turkey. However, she may feel it is easier to lift the turkey.

Ask Students: Can you think of other situations in which it would be an advantage to use a pulley to do work? Student answers will vary. A pulley can help move heavy objects. Pulleys are used to: move handicapped individuals from a wheelchair into a bathtub or into their bed, move car engines in and out of the car’s chassis, raise or lower hanging potted plants, etc.

Ask students: Can you remember the Rules derived from your data? If necessary, provide prompting terms such as work, mass, force, and simple machines or pulley.