Name ______Date ______Period ______

Work and Machines

Pulleys as Simple Machines

Objective

To discover how pulleys help raise objects and how to find the mechanical advantage of a pulley and a pulley system.

Hypothesis

Write an “If….then….” statement about how you think pulleys will change force, distance or direction to make work easier:

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Materials

2 single pulleys

2 double pulleys

String or fishing line

Ring stand and large ring

Green Spring Scale

500 g mass

Procedure

  1. Calibrate the spring scale so that it reads zero Newtonswhen no masses are attached to it.
  1. Find the weight of the mass you are using in Newtonsby attaching it directly to the spring scale.
  1. Record this weight in the data table as the output force for all the pulley arrangements.
  1. Set up a single fixed pulley as shown in Figure 1.
  1. Pull down on the spring scale to lift the mass.
  1. The reading on the scale shows the amount of input force needed to lift the mass.
  1. Record this number in Newtons in the data table.
  1. To determine the ideal mechanical advantage of a pulley or pulley system without calculations, count the number of sections of rope that support the weight. The end section, which is attached to the spring scale, counts as a supporting section only when pulled upward. Look at your pulley system and determine its mechanical advantage, then record it in the data table.
  1. Set up a single movable pulley as shown in Figure 2.
  1. Lift the mass by pulling up on the spring scale.
  1. The reading on the scale shows the amount of force needed to lift the mass.
  1. Record this number in Newtons in the data table.
  1. Look at your pulley system and determine its ideal mechanical advantage, then record it in the data table.
  1. Set up the single fixed and sing movable pulley system shown in Figure 3.
  1. Measure the amount of force needed to lift the mass and record it in Newtons in the data table.
  1. Look at your pulley system and determine its ideal mechanical advantage, then record it in the data table.
  1. Set up the pulley systems shown in Figures 4 and 5 (the side-by-side pulleys work in the same way as the up and down ones).
  1. For each pulley system, measure the amount of force needed to lift the mass and record it in the data table.
  1. Look at your pulley systems and determine each one’s ideal mechanical advantage, then record them in the data table.
  1. Calculate the actual mechanical advantage for each pulley by dividing the output force by the input force) and record in the data table.

Analysis

  1. Was there a difference in the ideal mechanical advantages you calculated for single fixed pulley and the single movable pulley? Give a reason for your answer.

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  1. As you added pulleys to the system, what happened to the amount of input force needed to raise the mass? Explain why.

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  1. Although the amount of input force needed to lift a mass is usually less in a pulley system, something else increases. What must increase as the input force decreases?

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  1. Look at the cartoon below. According to what you learned from this lab, why does this not make sense?

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Conclusion

The conclusion section needs to have five sentences:

1st sentence: Repeat the objective

2nd sentence: Describe what you did specifically in the lab to achieve the objective.

3rd sentence: State your hypothesis and use your data to explain if it correct or not and why.

4th sentence: Share what you learned.

5th sentence: This is a general summary of the lab. It ties into the first sentence of the purpose.

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Data Table

Figure / Pulley Arrangement / Output Force (N) / Input Force (N) / Actual Mechanical Advantage
(output force ÷ input force) / Ideal Mechanical Advantage (number of sections of rope)
1 / Single Fixed
2 / Single Movable
3 / Single Fixed and Single Movable
4 / Double Fixed and Single Movable
5 / Double Fixed and Double Movable