FRICTION PERFORMANCE ASSESSMENT

Transcription

1 1 FRICTION PERFORMANCE ASSESSMENT SECTION I Your Name: (Last) (First) Male or Female Date of Birth: (please circle) (month day year) Today's Date: (month day year) INSTRUCTIONS In this activity you will be working by yourself. You can write your answers directly on these pages. Before you look at the equipment in the bag in front of you, we want you to think about the concepts of force and motion.

2 PART I: Planning and Design 2 Suppose you have to pull a wagon along a driveway. Will it be easier or harder to pull a wagon along a concrete driveway or a gravel driveway? Why?

3 3 The amount of force you need (how much you have to push or pull) to move an object along a surface depends on the texture of the surface. Different surface textures cause different amounts of FRICTION. Friction slows down and stops moving objects. Rougher surfaces cause more friction than smoother surfaces. That means it will take more force to pull the wagon along a gravel driveway than a concrete driveway. Another thing to know!!!! The amount of force you need to move an object along a surface depends on the weight of the object. Let's say you now had to pull a wagon full of bricks along a concrete driveway. This time you would have to pull harder because the wagon is heavier.

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5 Now you can take the equipment out of the box in front of you. You should have the following things: 5 EQUIPMENT 2 wooden blocks with hooks String with hook 1 plain wood board with eye hook 1 felt covered board with eye hook 1 sandpaper covered board with eye hook Washers Put the plain wood board on the table. The end with the eye hook should be at the edge of the table. It should look like this:

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7 Now put one of the blocks with the "B" side down on the board. Place it behind the red starting line. Take the string with the hook and pull it through the eye hook. Now loop the string on the hook on the block. It should look like this: 7 Notice that the blocks are different weights and the BOARDS have different surface textures. Practice pulling one of the blocks along the board by putting washers on the hook. The back end of the block should cross the starting line. Putting washers on the hook is a measure of the amount of force needed to pull the blocks. MORE WASHERS = MORE FORCE

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9 Sue and Maria want to know whether they will need different amounts of force to pull the blocks of different weights along the plain wood board. 9 Suppose it takes 4 washers to pull the lighter block. Will you have to add more washers or less washers to the hook to pull the heavier block? How does the amount of force needed to pull the block change when the weight of the block changes?

10 10 Now let's think about a different problem. Let's only use the large block. Sue and Maria have different ideas about how much force they would need to pull the block along the 3 boards. Sue thinks that the amount of force needed to pull the block depends on the surface texture of the board. The rougher the surface, the more force she will need to pull the block. BUT Maria doesn't think that changing the surface texture matters. She thinks that the amount of force needed to pull the block will be the same for each board. Can you think of an experiment you could do to test who is right? You can use the equipment in front of you to figure out how you could design an experiment. BELOW, write down the steps you would follow to do your experiment (if you need more space, you can write on the BACK of this page). 1

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12 PART II: Performance 12 Now let's see who is right. REMEMBER: Sue thinks that the amount of force needed to pull the block depends on the surface texture of the board. The rougher the surface, the more force she will need to pull the block. BUT Maria doesn't think that changing the surface texture matters. She thinks that the amount of force needed to pull the block will be the same for each board. Use the equipment in front of you to test if Sue is right or Maria is right. Write down your results in the table below. SURFACE TEXTURE (Board) FORCE (Number of Washers) PLEASE RAISE YOUR HAND FOR

13 13 SECTION II OF THE TEST

14 14 FRICTION PERFORMANCE ASSESSMENT SECTION II Your Name: (Last) (First)

15 PART III: Analysis and Interpretation 15 Sue and Maria conducted an experiment to test out their ideas. They used a block, a string with a hook, 1 plain wood board with an eye hook, 1 felt board with an eye hook, 1 sandpaper board with an eye hook, and washers as a measure of force. This is what they did: 1. They put the block on the plain wood board behind the starting line so that the hook on the string hung over their table. 2. They added washers to the hook until the back end of the block moved past the starting line. They wrote down how many washers it took. 3. They did steps 1 and 2 with the other boards.

16 Sue and Maria wrote down their results in the table below. 16 SURFACE TEXTURE (Board) FORCE (Number of Washers) Plain 8 Felt 12 Sandpaper 17 Use the information from the table to graph the findings from Sue's and Maria's experiment. FORCE (Number of washers) SURFACE TEXTURE (Board)

17 Think about the results Sue and Maria got. How did the amount of force needed to pull the block change when the surface texture changed? 17

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19 PART IV: Application 19 Mrs. Brown has a storage company where big, heavy objects always need to be moved. In Mrs. Brown's company, the floor is very smooth so that the workers can easily slide the heavy objects across the floor. Mrs. Brown has a problem. Last year 12 workers slipped on the floor and hurt themselves. Mrs. Brown needs to figure out how she can stop the workers from getting hurt. Before she can decide on a solution, she has to think about two things: 1. Heavy objects need to be moved easily across the floor. 2. Mrs. Brown doesn't not have lots of money to buy expensive equipment to move the heavy objects. The problem is how to stop the workers from slipping and falling on the floor.

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21 Before you think about how you would stop the workers from slipping and falling, let's review what you learned earlier. 21 In the activity you did earlier, you looked at the relationship between surface texture and the amount of force needed to pull a block on that surface. What you should have noticed was that the rougher the surface, the more force it took to pull the block on that surface. In this new problem, Mrs. Brown has to figure out how to stop her workers from slipping and falling on the floor. However, she has to be able to move heavy objects across the floor. She also doesn't have lots of money to spend on expensive equipment to move the heavy objects. You have been hired by Mrs. Brown to help her find a way to stop her workers from slipping and falling on the floor. Using what you learned in the activity you did earlier, please write down what you would tell Mrs. Brown to do. Be sure to carefully explain to Mrs. Brown why you chose the solution that you did. PLEASE WRITE YOUR ANSWER ON THE NEXT PAGE.

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