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5.1 Work

5.1 Work. pp. 168 - 171 Mr. Richter. Agenda. Warm-Up Collect Proposals Discuss Remainder of Term 2 Notes: Definition of Work Work Formula Calculations with Work Begin HW. Objectives: We Will Be Able To….

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5.1 Work

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  1. 5.1 Work pp. 168 - 171 Mr. Richter

  2. Agenda • Warm-Up • Collect Proposals • Discuss Remainder of Term 2 • Notes: • Definition of Work • Work Formula • Calculations with Work • Begin HW

  3. Objectives: We Will Be Able To… • Recognize the difference between the scientific and ordinary definitions of work. • Define work by relating it to force and displacement. • Identify where work is being performed in a variety of situations. • Calculate the net work done when many forces are applied to an object.

  4. Warm-Up: • Which force do you think does the most work on the crate? Guess, even if you don’t know what work means in the physics sense.

  5. Work

  6. Work • Work is done any time an object is displaced some distance by a force. • More simply: Work = Force x Displacement • Work is done: • to push a car down the road • to lift an object up to a high shelf

  7. Work is not the same as effort • Examples of not-work: • A student holds a heave chair at arm’s length for several minutes. • Chair doesn’t move. No displacement = no work done on the chair. • A student carries a bucket of water along a horizontal path while walking at a constant velocity. • Constant velocity. Fnet = 0, no work done on the bucket.

  8. Work • Work is only done when components of force are parallel to displacement. • A. No work. • B. Some work. • C. Most work.

  9. Work • To find the component of force parallel to displacement, use cosine! • When the angle is 0°, W = Fd • When the angle is 90°, W = 0

  10. Calculating Work • Determine the net force. • Use the formula. Watch your signs. ‘Nuff said.

  11. Units of Work • If work is force x distance, the units are Newtons x meters. • N-m • Physicists abbreviate this as a Joule [J]

  12. Practice • How much work is done on a vacuum cleaner pulled 3.0 m by a 50.0 N force at an angle of 30.0° above the horizontal? • In this case, the net force is the same as the given force. In other cases, you may need to calculate the net force first. • W=(50.0N)(3.0m)(cos30.0) • W=130 J

  13. Wrap-Up: Did we meet our objectives? • Recognize the difference between the scientific and ordinary definitions of work. • Define work by relating it to force and displacement. • Identify where work is being performed in a variety of situations. • Calculate the net work done when many forces are applied to an object.

  14. Homework • p171 #2-6

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