Investigation 5 is the final regular Investigation for the LabLearner CELL Work and Simple Machines. This Investigation focuses on the inclined plane as a simple machine.

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Begin this part of the investigation by reviewing the experiments students performed in the lab. Ask the following questions to promote discussion of the experiments.

What is an inclined plane? An inclined plane is a simple machine that connects a lower point to a higher point with a straight surface.

What was the theme or focus of the investigation? Students investigated the effort used to lift an object using an inclined plane. They also compared the effort applied and work done on inclined planes of the same height but varying length (variations in the steepness of the incline).

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Prompt student discussion by asking the following questions. Encourage students to refer to Trials 1 and 2 in their Scientist Data Record.

Ask students: What question did you answer when performing Trial 1? How much force did you exert to lift the load?

What question did you answer after moving the load in Trial 2? How much force did you exert to lift the load using an inclined plane?

Did you lift the same load in Trials 1 and 2? Was the mass the same? The load lifted was the same in both Trials. This is because the mass of the bucket and its contents were the same for both Trials.

Did you lift the load to the same height in Trials 1 and 2? Why? The load was moved to the same height in each Trial. Even though the load moved over an inclined plane in Trial 2, it still ended 8 cm above the table. This was the same height the load was lifted in Trial 1.

Was there a difference in the amount of effort you applied to lift the load when you used the inclined plane (Trial 2) as compared to when you did not (Trial 1)? There was a difference between the effort needed to lift the load with an inclined plane versus the effort needed to lift the same load without an inclined plane. The effort needed to lift the load in Trial 2 (using the inclined plane) was less (0.7N) than the effort needed in Trial 1 (2.6N) (not using an inclined plane).

Did you test the effort when using any other inclined planes? Both Trials 3 and 4 tested the effort using inclined planes that were a different length than the one used in Trial 2. Trial 3 used an inclined plane with the same height but shorter length than the inclined plane in Trial 2. Trial 4 also used an inclined plane with the same height but shorter length as the inclined planes in Trials 2 and 3.

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Ask students: Can you make a conclusion about the effort needed to lift an object compared to without an inclined plane? 

Ask: How could you organize your data to help you draw conclusions from Trials 1 – 4?

Direct students to look at the first Table of their Scientist Data Record (shown in this slide).

Discuss the rows and columns in the Table. Explain that some of the information in the table such as the number of the Trial and the use of the inclined plane has already been provided.

Encourage students to work individually to complete the Table by adding information about the effort applied in Trials 1-4.

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As class walk through the process of comparing the conditions that existed for each of the trials. Refer to the table that students completed during the discussion. Encourage students to complete the questions that follow the table at the relevant points during the class discussion.

Did you lift the same load in Trials 1-4? Was the mass the same? Yes. The load remained unchanged throughout the entire Investigation.

Did you lift the load the same distance (height) in Trials 1-4? Why? Yes. Each time the load was moved, it ended 8 cm above the table.

Was the effort you applied to lift the load when you used the inclined plane (Trials 2, 3 and 4) the same as when you did not (Trial 1)? No. The effort needed to lift the load using an inclined plane (0.7N, 0.8N, 0.9N) was different from the effort needed to lift the load without using the inclined plane (2.6N)

Did using an inclined plane change the amount of effort needed to lift a load 8 cm off of the ground? Using an inclined plane reduced the amount of effort needed to lift a load 8 cm off of the ground. In Trial 1, 2.6 newtons of force were needed in order to elevate the load 8 cm off of the ground. In Trials 2-4 when the inclined plane was used, it was 0.7N, 0.8N, and 0.9N. In each Trial that the inclined plane was used, the load was still lifted 8 cm but the effort was always less than 2.6 newtons.

How does using an inclined plane affect the effort needed to lift a load? If the load is lifted the SAME HEIGHT with and without the inclined plane, it will take less effort to move the load with the inclined plane as compared to without the inclined plane. Students might suggest that if the height DIFFERS between the two conditions, the effort used to move a load along an inclined plane may be the same or greater than to lift a load a smaller distance off of the ground.

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Begin a more in-depth analysis of Trials 2, 3, and 4 in order to understand why there was a difference in effort when using the inclined plane and why the effort differed when different length inclined planes were used in Trials 2, 3, and 4. 

Use the following questions to lead a discussion about the experiments (students may want to refer to their Student Data Record as the trials are discussed):

Think about Trial 2. What question did you answer when performing Trial 2? How did you answer this question? Students investigated the question: Will an inclined plane change the amount of effort needed to lift a load 8 cm off of the ground? To answer this question, students constructed an inclined plane out of meter sticks and a small accessory box. Students measured the amount of effort needed to lift a load 8 cm up an inclined plane 80 cm in length.

Now think about Trials 3 and 4. What questions did you answer when performing Trials 3 and 4? Students investigated the question: Will decreasing the length but not the height of an inclined plane change the amount of effort required to lift the bucket? Will decreasing the length, but not the height of an inclined plane change the amount of work needed to lift the bucket 8 cm off the table? To answer these questions, students modified the inclined plane that they constructed in Trial 2 by decreasing the length. The height of the inclined plane, however, remained the same (8 cm). They then measured the effort force using the same procedure from Trial 2. Students then calculated the amount of work performed on the different length inclined planes.

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Ask students: Can you create a Table using data Trials 2-4 to help you analyze the differences between the trials? How would you organize the table? Student answers will vary.

Model the construction of a Table with the class that presents their data in a meaningful format for analysis. Students should use the blank space under Problem 7 in their Student Data Record to complete their Table.

Before students create their table, discuss with them how a Table could help organize their data from Trials 2 through 4. Model how to create a data Table by explaining the decisions students will need to make in order to create the table. Use the following statements to help guide students in creating a table for their data:

Before creating a table for your data, you must decide what you need to record in the table.

• There were several Trials in the investigation, so you want a place in your Table to identify and record the data from each Trial. Since you have three Trials that use inclined planes, you should have three rows.
• You will need columns to record the data you collected from each trial, so you will need to identify the data needed in those columns.
• Since you recorded the length of the inclined plane, the height of the inclined plane, the distance the effort was applied, differences in the steepness of each incline, the effort, and work done in your data, you will need columns for each of these conditions.
• You must decide on appropriate titles for your columns.
• After discussing each of the steps, continue to the next slide that includes sample data to discuss.

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Upon completion of the data table, lead the class in an analysis of the information presented in the table.

1. Focus the first part of the discussion on the relationship between the different inclined planes and the effort applied when moving the load along each.

a. Look at the sample data in this Table. Previously, you observed (comparing Trials 1 and 2) that less effort was applied when using an inclined plane to lift a load rather than lifting it straight up. What other observations can you make about the effort from Trials 2-4? The height of the three inclined planes was the same, but the length of inclined planes in Trials 2-4 was different. The steepness of the three inclined planes was also different.

b. What caused the steepness of the inclined planes to change? All three of the inclined planes had a height of 8 cm; however, the length of each of the inclines was different.

c. How did changing the length of the inclined planes but not their height affect the steepness of each inclined plane? As the length of the inclined planes decreased, the steepness of the inclines increased.

d. Why do you think the effort differed in Trials 2-4? The steepness of the inclined plane affected the amount of effort needed to move the load. As steepness increased, the effort needed to move an object also increased. The inclined plane in Trial 4 was steeper than those in Trials 2 and 3. Trial 4 had the steepest incline and required more effort to move the load than the other inclined planes. The inclined plane in Trial 3 was steeper than that in Trial 2. More effort was required to move the load along the inclined plane from Trial 3 than from Trial 2 or Trial 1.

e. Why do you think the differences in the steepness of the inclined planes changed the amount of effort needed to move the load? Use what you know about levers, effort and effort arm length to help you answer the question. The differences in the steepness of the inclined planes from Trials 2-4 occurred because the height of the inclined plane was the same but the length of the inclined plane changed. When the length of the inclined plane was longer, the incline was less steep. When the length of the inclined plane was shorter, the incline was steeper. This means that when the object was pulled over the steeper incline, the distance over which the effort was applied was less than the distance the load was pulled over the less steep incline. For example, the inclined plane in Trial 4 was steeper than the inclined plane in Trial 2. As a result in Trial 4, the load was only pulled 60 cm, but in Trial 2, the load was pulled 80 cm. As the distance over which the load was pulled increased, the effort decreased. This is similar to the situation seen with the lever. There is an inverse relationship between the distance the effort is applied and the magnitude of the effort.

f. Think back to Trial 1. How could you explain the difference in effort when lifting the load to the same height without as compared to with the inclined plane? When the load was lifted with the inclined plane, the distance the effort was applied (80 cm, 70 cm or 60 cm) was greater than the distance the effort was applied (8 cm) when an inclined plane was not used. As the distance over which the effort was applied increased, the effort to lift the load decreased.

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Ask students: Can you think of another way to illustrate the differences in the effort compared to the differences in the distance the load was pulled? Guide students to the realization that a line graph can be used to compare the change in effort to the change in the distance the load was pulled (length of inclined plane).

Instruct students to use the graph in their Scientist Data Record to plot the data. Model the process of creating a line graph.

Review and use the steps below to walk students through this process. Use the Create and Complete a Line Graph from the Procedural Toolbox if necessary.

• Draw an x-axis and a y-axis.
• Decide which variable to plot on the x-axis and which variable to plot on the y-axis.
• Label the axes appropriately.
• Decide the beginning and ending numbers to place on the x-axis and y-axis. The numbers should allow all the points to be plotted on the graph.
• Decide the scale for each axis.
• Graph the data and connect the points with a line.

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Focus the second part of the analysis on the work done during Trials 2-4:

Compare the work done when lifting the load with each of the inclined planes. Is the work the same?  Yes. Note: that some students will point out that the work done did change for each Trial. Tell students to compare the values of the work done for each Trial, having them examine how close the values are for each of the Trials. A brief discussion on the margin of error might be necessary to show the students that the numbers are close enough to be considered the same.

Why do you think the work was the same when the load was moved along inclined planes that had different lengths? Student answers will vary.

What two factors affect the amount of work done on an object? The effort applied to the load and the distance over which the effort is applied.

Did the distance the load was pulled and the effort change in the same direction? In other words, when the length of the inclined plane increased did the effort also increase? No. Students should indicate that as the length of the inclined plane increased, the effort required to move the load decreased. As the length of the inclined plane decreased, the effort required to move the load increased.

Why was the work the same? The work was the same because of the inverse relationship between the effort and the distance the effort was applied. Recall that Work = Force x Distance. As the length of the inclined plane decreased, the distance over which the effort was applied decreased. At the same time, the amount of effort needed to be increased. Because distance decreased as the force increased, the work done remained the same.

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Ask students what conclusions they can make about the effort used and work done to move the load the same height, but along inclined planes of different lengths. Students should record their Conclusions in their Student Data Records.

How does the steepness of an inclined plane affect the effort required to lift a load? What determines the steepness of an inclined plane? As the steepness of an inclined plane increases, the effort required to move a load along the inclined plane increases. An inclined plane becomes steeper when its length is shortened but its height is kept the same.

How does changing the length but not the height of an inclined plane affect the work done to lift a load? Why? If HEIGHT of the inclined planes is the SAME, it will take the same amount of work to move the load. The work is the same because the effort to move the load increases as the distance the effort applied to move the load decreases. For example, the 80 cm long, 70 cm long, and 60 cm long inclined planes were all 8 cm in height. The work done to move the load along each of these inclined planes was the same. The work was the same (0.56 J) as the length of the inclined plane decreased because the effort to move the load increased (0.7N, 0.8 N, 0.9N) as the distance the effort applied to move the load decreased (80 cm, 70 cm, 60 cm).

Students should suggest that if the height differs between the inclined planes, the work done to move the loads along an inclined plane may differ.

Finally, complete the Post-Lab by having students use the information from this Investigation to determine the answers to the following two questions regarding the three inclined plane triangles on this slide:

Which of the inclined planes shown would require the least effort to lift a load 1 meter? Inclined Plane 3

Would any of the inclined planes require more work to lift a load 1 meter into the air? All three inclined planes would accomplish the same amount of work to lift a load one meter into the air.