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Students will compare how much force is needed to lift objects without a pulley, then how much force is needed with a pulley.
Lift The Load
For each group:
A simplified definition of work is to make an object move or to change it’s motion. Simple machines are devices that make work easier. All simple machines transfer force. Some change the direction of force, while others change the strength of the force. Still others change both the direction and the strength. Most simple machines make work easier by allowing you to use less force over a greater distance to move an object. Some machines make work easier by allowing you to move things farther and/or faster. In these machines, a larger force is required, but over a shorter distance.
It would be preferable to include more than one pulley system, but due to the nature of the activity, it would involve a considerable amount of time for the students to attempt to build a more complex pulley system. This activity is adequate as a simple comparison between working with and without a pulley.
The invitation to learn is an example of a wheel and axle.
1. Use Science Process and Thinking Skills
2. Manifest Scientific Attitudes and Interests
3. Understand Science Concepts and Principles
4. Communicate Effectively Using Science Language and Reasoning
Invitation to Learn
Students observe as you place what seems to be an ordinary can on a table. Tell them to watch its movements very carefully. Begin with the can sitting on the table. Focus attention to the fact that it is still and will not move by itself. Next, roll the can gently. It will return to you. Have the students try to figure out why the can returns when it is rolled. You may explain it and show what is happening, or leave it a mystery.
Explanation: The can stores energy in the rubber band because the weight remains in position as the rubber band twists. When the can stops rolling forward, the stored energy in the twisted rubber band propels the can in the opposite direction.
To make a returning can:
Explore how a wheel and axle work to make work easier. Will a wheel and axle make homework easier? Probably not, but it does make some mechanical work easier. Prove this by learning how a wheel and axle work as part of another simple machine called a pulley. Compare how much force is needed to lift objects without a pulley, then how much force is needed with a pulley.
Model for the students and explain how to build the system:
Assist groups as necessary in constructing pulley systems and beginning the experiments.
Have students compare the force needed to lift their items with and without the pulley system. Log the results on the Lift the Load worksheets and draw conclusions about how pulleys make mechanical work easier using the wheel and axle.
Joritz-Nakagawa, J. (1992). Spencer Kagan’s Cooperative Learning Structures. 2nd Peace as a Global Language Conference Proceedings & Supplements, 7-8.
This paper discusses Spencer Kagan’s approach to cooperative learning, which is structured peer interaction and collaboration to achieve a purpose. There are countless structural possibilities that can be used in any learning situation. The article gives examples of some structures. It also mentions structuring activities to involve multiple intelligences to make learning meaningful and accessible to students.