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Work and Power

Work and Power. What is work?. Definition : energy transferred by a _____________ to move an object a _____________ (when both the force and the motion of the object are in the same direction.). Work or Not?. According to the scientific definition, what is work and what is not?

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Work and Power

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  1. Work and Power

  2. What is work? • Definition: energy transferred by a _____________ to move an object a _____________ (when both the force and the motion of the object are in the same direction.)

  3. Work or Not? • According to the scientific definition, what is work and what is not? • a teacher lecturing to her class • a mouse pushing a piece of cheese with its nose across the floor

  4. Work or Not? • According to the scientific definition, what is work and what is not? • a teacher lecturing to her class • a mouse pushing a piece of cheese with its nose across the floor

  5. Work or Not • Why?

  6. What’s work? • A scientist delivers a speech to an audience of his peers. • A body builder lifts 350 pounds above his head. • A mother carries her baby from room to room. • A father pushes a baby in a carriage. • A woman carries a 20 kg grocery bag to her car?

  7. What’s work? • A scientist delivers a speech to an audience of his peers. No • A body builder lifts 350 pounds above his head. Yes • A mother carries her baby from room to room. No • A father pushes a baby in a carriage. Yes • A woman carries a 20 km grocery bag to her car? No

  8. Formula for work Work = _________ x Distance • The unit of work is newton x meters • One ____________ is equal to one ______ • So, the unit of work is a __________ • J= 1 N x m = 1 kg x m2/s2

  9. W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

  10. W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? 200 joules (W = 20N x 10m)

  11. Power • Power is the __________ at which work is done. • Power = Work*/Time or P= W/t • The unit of power is the watt. • 1 watt= ______________

  12. Work vs. Power • Work vs. Power

  13. Concept Check • 1. Describe the difference between work and power? • 2. How is work being done in the following situation • Powerlifting • Dropping your textbook • Doing a handstand • What is the unit for lightbulbs? Why is that unit used?

  14. Math Practice • 1. A crane use an average force of 5300 N to lift a girder 25 m. How much work does the crane do on the girder? • 2. Aylssa powerlifts Kyle over her head 1 m with a force of 250 N. How much work was done? • 3. While rowing in a race, John uses his arms to exert a force of 165 N per stroke while pulling the oar 0.800 m. How much work does he do in 30 strokes?

  15. Math Practice • 4. While rowing in a race, John does 3960 J of work on the oars in 60.0 s. What is his output in watts. • 5. Steve using a jack does 4320 J of work to lift a car 1.5 m in 100.0 s. What is the power output? • 6. Mr. Farrell walks up the stairs on his way to make copies. He weight 622 Newtonsand the stairs go 5.75 vertically. a. Calculate my output if I climb the stairs in 8.9s. b. What is I climb the stairs in 7.2 s?

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