University of Virginia
Physics Department

## Pulleys

A Physical Science Activity

Student Activity

Materials

 ½ meter stick or ruler Rope, 70 cm long Binder clip, medium size 2 Paper clips Spring scale, 10 N max. Cardboard, 50x50 cm Gravel (240 g) per bottle White paper Rubber band Masking tape 2 Single pulleys 2 Plastic bottles with screw eye in lid, 500 ml (can be ordered from Delta Education Foss Catalog (1-800-258-1302); item number 420211232)

Procedure

1. Hang one spring scale from another. Read the measurement from the top scale (the top of the curved line) and record it on the data table.
2. Fill each plastic bottle with gravel. Check the mass on a scale; if it is not 240 g, add water until the mass is corrected.
3. Cut the cardboard into two pieces. One should be 30x50 cm, the other 20x50 cm.
4. On the smaller piece of cardboard, trace the size of the lid of a plastic bottle. Cut a square around the shape, and then cut the shape of the lid from the cardboard. This square should be placed on the bottle before the lid is screwed on.

5. Tape two pieces of white paper on the larger piece of cardboard, one above the other. On the lower sheet, use a ruler to mark dashes at 5 cm, 10 cm and 15 cm from the bottom of the cardboard. Draw lines across the paper at these dashes.

6. Clip the binder clip to the end of the ruler, so that the metal rings face towards you.
7. Tape the ruler to a desk or table so that the clip hangs over the edge of the surface. Set a book on the ruler to ensure that it doesn't slide off.
8. Fold 5 cm from the end of the rope over into a loop and secure the loop with masking tape. Repeat on the other end of the rope.
9. Construct a fixed pulley. First, attach the pulley wheel to the binder clip on the edge of the surface. Thread the rope through the pulley. From one end of the rope, hang the load. From the other, hang the spring scale.

10. Lift the load and record the required effort. Add this to the weight measured in step 1 of the spring scale.
11. Now construct a movable pulley. To do this, attach one end of the rope to the binder clip. Thread the rope through the pulley wheel, and attach its other end to the spring scale. Hang the load from the wheel itself. For a movable pulley, the load should be hanging from the center of the rope, and the spring scale should be above it.

12. Lift the load and record the required effort. Add to this the weight of the spring scale measured in step 1.
13. Retrieve the large sheet of cardboard with the white paper on it. Tape this sheet to the side of the table or counter, directly underneath the binder clip.
14. Set up a fixed pulley system as you did in step 5.
15. Hang the load from one end of the rope. Put a pencil through the loop at the other end (instead of the spring scale).
16. Apply effort to the pencil so that the load hangs at the lowest (5cm) line drawn on the white paper. Use the cardboard collar on the load to judge this.
17. Keep the pencil in the rope loop for the rest of the experiment. While the load is positioned at the 5cm line, draw a line on the white paper with the pencil where it hangs.
18. Drag the pencil down the paper, drawing a line while lifting the load so that the collar reaches the top line (15cm).
19. Release the load. Measure the distance traveled by the effort (the pencil line on the paper). Record this on the data table.
20. Set up a movable pulley system as in step 8. Hang the load from the pulley. Again, replace the spring scale with a pencil.
21. Repeat steps 12-14. With this setup, however, the pencil will move up along the paper.
22. Record the distance traveled on the data table.

Data Sheet

 Force of spring scale itself: Direction of Effort Load (N) Effort (N) + spring scale force Effort Distance Load Distance Fixed Pulley Movable Pulley

Questions

1. Is there a difference in the effort required to lift a load when using a fixed pulley and a movable pulley? Explain.

2. Did the effort distance differ when using the two types of pulleys? Why or why not?

3. Describe a situation in which it would be to your advantage to use a pulley instead of another type of simple machine.