Pull Toy

INTRODUCTION

The goal of this experiment is to demonstrate the combined use of multiple movable pulleys.

MATERIALS

• 2 7/8" diameter dowel rods
• 20' of rope or more

WHAT TO DO

1. Tie the rope around the barrel of one of the dowel rods.
2. Have two students hold the dowel rods parallel to each other. The dowel rods should be about 2 feet apart.
3. Next, wrap the rope back and forth between the two dowel rods two times.
4. While the students holding the dowel rods try to pull them away from each other, ask another student to pull on the loose end of the rope to try to pull the dowel rods together.
5. Wrap the rope back and forth between the dowel rods four more times. Ask the students to try pulling again. Does it feel different this time?
6. Wrap the rope back and forth between the dowel rods four more times and try again.

QUESTIONS

1. Which student controls the distance between the two rods?
2. Why?
3. What does this tell us about how pulleys work?

SUMMARY

Each time the rope travels from one dowel rod to the next the force necessary to move the rod decreases because each wrapping of the rope acts as a pulley. If there are four complete loops across, that corresponds to 8 strands moving from one rod to the next. The force necessary to move the rods is divided evenly between the number of strands of rope. Therefore the force necessary to move the rods should be decreased by a factor of 8 with 8 strands.

SOURCES

"Pulley Activities." NES Arnold, World Class Learning Materials, Baltimore, ISBN: 1-884461-08-5.
"Simple Machines Made Simple." Ralph St. Andre, Teacher Ideas Press, 1993, ISBN: 1-56308-104-0.

Grade Level: Grades K-5

© S. Olesik, WOW Project, Ohio State University, 2001.