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South Carolina ETV
1101 George Rogers Boulevard
Columbia, SC 29201-4761
Phone: 803-737-3545

Work in Linear Mechanical Systems (Grades 11-12)

MASTER TEACHER

Robert Sheffield

OVERVIEW

The purpose of this lesson is to introduce the students to the topic of mechanical work. Through the use of the video, the students will discover how the force exerted on an object and the distance the object moves determines the work done on the object. The students should conclude that without movement, there is no work done. Additionally, the students should be able to state the units associated with work. A follow-up activity will provide the students with practice in calculating mechanical work by having them determine the amount of work required to climb a set of stairs.

ITV SERIES

Principles of Technology, Lesson 2: Work

LEARNING OBJECTIVES

The students will be able to

• identify the units associated with linear work
• calculate the work done on an object

SC MATH/SCIENCE STANDARDS MET

This lesson provides the students with additional exposure to the following High School process skills standards:

• Observe - make quantitative observations
• Measure - Use metric units and/or SI units
• Design, Conduct, and Evaluate a Scientific Investigation - Analyze data to construct explanations and conclusions

MATERIALS
(1 per group)

• stop watch
• measuring
• tape calculator

PRE-VIEWING ACTIVITY

Have the students hold a 5-10 kg mass with their arms extended straight out. Ask them to try and not move the weight and keep it perfectly still. After 30 seconds, ask the students if they have done any work as they held the mass. In spite of their muscular strain, inform the students that they have not done work according to the definition of Work. According to the equation "Work = Force x Distance," there was no work done on the mass because the mass did not move.

FOCUS FOR VIEWING

To give the students a specific responsibility while viewing the video, have the students write down all the examples of work they can find in the video. The students should be able to easily find five examples.

VIEWING ACTIVITIES

The video begins with the title screen "Work in Mechanical Systems" and a scene of weight lifters in a weight room.

Stop the video when the video shows an arm flexing and the announcer states "To do work in a mechanical system, two things are needed." Have the students predict what the two things are. Resume video.

Stop the video when the announcer states "Watch this scene and see when work is being done." Have the students give the thumbs up sign when work is being done, and the thumbs down sign when work is not being done. When the video replays the scene, the students will be able to assess if they were correct with their predictions. Resume video.

Stop the video when the announcer states "Now watch the robot." Have the students repeat the procedure of giving the thumbs up symbol when work occurs and the thumbs down sign when no work occurs. The scene will, again, replay itself in order for the students to assess their predictions. Resume video.

Stop the video when the elevator reaches the top floor. Explain that the work required to lift the elevator is not affected by the additional time needed to stop and hold the elevator at each floor. Additionally, inform the students that lifting the elevator faster or slower will not affect the amount of work required to lift the elevator. Resume video.

Stop the video during the scene of a barrel being lifted by a block and tackle when the announcer states "work is being done." Explain that the force exerted by the man multiplied by the distance the rope moves is the work in. Also explain that the force of the weight of the barrel multiplied by the distance the barrel moves is the work out. To find the efficiency divide the work out by the work in and multiply by 100%. Resume video.

Stop the video when the announcer states "No machine is perfectly efficient." Have the students predict where the lost work goes.

The video clip concludes with the scene of a crane on top of a building.

POST VIEWING ACTIVITY

In groups, the students will calculate the amount of work needed to climb a set of stairs. The bleachers of a football stadium can be used to allow several groups to perform this activity concurrently. A new topic of "power" should be introduced prior to the performance of this activity. Define the concept of power as the rate at which work is done. To find this measurement, divide the work done by the time required to perform the task. The students should be cautioned to not run while completing this activity, due to the possibility of injury. Use Activity Sheet 1.

ACTION PLAN

Have the students contact a local construction company that utilizes a crane. Have them ask the company the maximum weight the crane can lift and the maximum distance the load can be lifted. Using this information, the students should be able to calculate the maximum work load of the crane. The students should then compare this measurement to the amount of work they performed in climbing the stairs.

Activity Sheet (PDF)

• Activity Sheet 1