Simple Pulleys

INTRODUCTION

Pulleys can be used to reduce the amount of force needed to do work or to change the direction of the force. This activity provides a simple example to help young students understand pulleys and their functions.

MATERIALS

• Broom handle or thick dowel rod
• Rope
• Milk bottle or detergent bottle with handle, filled with water or sand

WHAT TO DO

1. Secure the ends of the dowel rod to the tops of two desks spaced about 3 feet apart.
2. Hang the rope over the dowel rod and tie one end of the rope to the handle of the milk jug.
3. Pull down on the other end of the rope to lift up the milk jug. This is a fixed pulley system that is used to change the direction of the force needed to lift the milk jug.
4. Untie the milk jug. Thread the end of the rope through the handle of the jug, and then tie that end of the rope to the dowel rod. Lift up on the loose end of rope to lift up the milk jug. This is a movable pulley system. How does the amount of force used here compare to the amount used to lift the jug in step 3?
5. Loop the loose end of rope over the dowel rod and pull the end down to lift the milk jug. This is a combination of movable and fixed pulley systems. Does this arrangement of pulleys make it easier to lift the milk jug?
6. Try looping the loose end of the rope over the dowel rod one or two more times. Is it easier to lift the milk jug?

QUESTION

1. Do pulleys make it easier to work? How?

SOURCE

"Sailboats, Flagpoles, Cranes: Using Pulleys as Simple Machines." Christopher Lampton. Millbrook Press, Brookfield: 1991. ISBN 1-56294-026-0

© S. Olesik, WOW Project, Ohio State University, 2003.