OBJECT:

To compare the mechanical advantage of a fixed pulley with a movable pulley.

* CAUTION *

This experiment has the potential of eye injury !! Be sure to wear your Safety Goggles at all times.

MATERIALS:

Safety goggles, Set of heavy books to be placed at the base of the stand, Make sure that your PVC pipe section and the right angles are snug, Set of weights (small plastic bags with 40 pennies = 100 g, 80 pennies = 200 g, 120 pennies = 300 g, 160 pennies = 400 g, and 200 pennies = 500 g) spring scale (rubber band scale ) String or twine, Two foot PVC stand, 4 inch PVC pipe extension, bolt and wing nut, One large nut.

PROCEDURE & OBSERVATION:

1. Set up your Two foot PVC stand, like you did in the "Pendulum" lab, but this time, insert your 4 inch extension with bolt and wing nut so it is horizontal to the stand. ( see diagram )

2. Attach a paper clip to the top hole of the pulley frame, then secure the paper clip to the bolt that is an the end of the 4 inch PVC pipe extension.

3. Obtain a piece of twine (string) about 70 cm long ( suggestion, you can use twine that is used in knitting or crocheting) strong enough to handle the weight, but small enough to fit into the groove of the pulley. Make a loop at each end of the twine, attach a 100 g resistance ( small bag with 40 pennies ). Pass the twine over the pulley, and at the other end attach your calibrated rubber band scale.

4. Be sure to adjust the rubber band scale to zero, now lift the 100 g weight several inches off the table top by pulling down with your rubber band scale and observe the reading on the rubber band scale and record it in the table. This is your Effort, it showsthe Effort needed to overcome the Resistance.

5. Now, repeat step number 4 using the weights shown below, and record the Effort needed to lift the Resistance.

6. Disassemble the fixed pulley set up.

7. Now, attach one end of the twine with the loop, to the bolt and wing nut, or slip the loop behind the bolt and wing nut, ( this can be done by making a lasso loop) over the 4 inch pipe, so that it will not slide off.

8. Hold the pulley frame by the hole that does not have the paper clip and pass the other end of the twine under the pulley wheel; attach a Resistance of 100 g to the paper clip.

9. Attach your rubber band scale to the other end of the twine, again the rubber band scale will be your Effort. Now, pull upward on the rubber band scale, until the weight ( Resistance ) is lifted off the table. Record the number of grams indicated on the rubber band scale.

10. Now, repeat step number 9 using the weights shown below, and record the Effort needed to lift the Resistance.

11. The object now is, try to measure the distance that the Resistance moves, and the distance that the Effort moves. To do this, you will need to use your two foot beam from the First class lever, which already has the metric strip attached to it.

12. Now, using One large nut, with string loop, so you can attach the paper clip to it ( Do not use a rubber band scale for this ) with your 2 foot metric PVC pipe in back of the Movable Pulley, pull straight up on the twine, so that both sides of the twine are parallel without lifting the weight, ( the bottom of the Large nut is just barely resting on the table), record the height of the bottom part of the loop, ( that you are holding ) , _________ cm. ( you may have to make a new loop, that will shorten your working distance ) Now raise the Resistance so that the bottom of the weight is 10 cm high. Now record the new height of the loop ________cm, subtract the first height that you got from the second height that you got. What is your answer ? __________ cm.

QUESTIONS:

1. What is the Formula for finding the mechanical advantage of a simple machine, when Resistance and Effort are known?

2. What is the Formula for finding the Mechanical Advantage of a simple machine, when only the distance of Resistance and distance of the Effort are known?

3. What is the mechanical advantage of a fixed pulley?

4. What is the mechanical advantage of a movable pulley?

5. What is the direction of Resistance and Effort in a fixed pulley?

6. What is the direction of Resistance and Effort in a movable pulley?

7. Find the mechanical advantage of a movable pulley using the information that you have in step # 12.

8. When force is gained, what happens to the distance? Explain.

9. List two examples where a fixed pulley is used.

10. List one example where a Movable pulley can be used ?

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