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Moveable Pulleys

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Lesson Focus

Moveable Pulleys

Physical Science

Learning Made Easy

You will get to explore the physics of levers, pulleys, inclined planes, and other simple machines. Learn to measure forces with a dynamometer and design your own pulley systems.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Explain how movable pulleys can be used to change the amount of force to move an object.

Everything You'll Have Covered

What are the parts of a movable pulley?

~ A movable pulley is made of a wheel with a large groove down the middle and a rope or wire that runs over the wheel and through the groove. The load is directly connected to the pulley's axel.

How does a movable pulley work?

~ A movable pulley works to lift a heavy object by applying an input force to the rope. When such a force is applied, the movable pulley begins to move through the rope by turning around throughout the rope. During this process, the tension of the rope is equal to the input force.

In a movable pulley, what is the relationship between the amount of work the input force does and the amount of work the output force does?

~ In a movable pulley, the amount of work the input force does and the amount of work the output force does is equal.

What does this tell us about how movable pulleys are used to change the amount of force needed to move an object?

~ Because the amount of work done by the input force and output force is equal in a movable pulley, there is no natural gain in force. Rather, the gain in force provided for by a movable pulley comes from applying the force over a longer period of distance; specifically, the input force must be applied over twice the distance of the output force.

Make one movable pulley system with the materials available to you. Try to lift one of your school materials (pencil, rubber, pencil case, etc.) with the use of a dynamometer and the pulley. Write down how much force is needed to pull the object you lift with the movable pulley, and make a conclusion about the results.

~ Answers may vary. Accept all reasonable responses. Students can make movable pulley systems by removing the bottom portion of a foam cup and using it as the groove of the pulley, and then wrapping a piece of string or rope around it. They can then pull a load with the movable pulley, with the use of a dynamometer. Then they should record the force as provided on the dynamometer. Finally, they conclude that the load's weight is equal to twice the measured force.

Tutorial Details

Approximate Time 2 Minutes
Pre-requisite Concepts Students should be able to define the following terms: pulleys, moveable pulleys, and mechanical advantage.
Course Physical Science
Type of Tutorial Animation
Key Vocabulary pulleys, moveable pulleys, mechanical advantage