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Physics Work and Power

This announcement provides important information about upcoming due dates for notebooks and emphasizes the importance of completing vocabulary and work. It also explains the concept of work in physics, including the formula for calculating work and its relationship with force, distance, and motion. Examples of work and power calculations are provided. The announcement also includes a brief history of horsepower and its relation to engines and electricity. Finally, example problems are given to further understand the concepts of work and power.

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Physics Work and Power

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  1. Announcements • Notebooks due: • 1st & 2nd DUE WEDNESDAY • 3RD & 4TH DUE THURSDAY • 7TH & 8TH DUE FRIDAY • MAKE SURE TO HAVE ALL VOCABULARY AND WORK DONE BY THE TIME YOU TURN IT IN. • END OF SIX WEEKS NEXT WEEK • Three more grades going in – notebooks, lab, one pager

  2. Work

  3. What does work mean to you?

  4. Work In physics, work has a very specific meaning. It is the action to make things change Work= force x distance W=F x d Unit: N-m : Joule

  5. W = F x d Therefore: You must have MOTION in order to have work… something has to change position

  6. Work = Force x distance

  7. Work …the motion has to take place parallel to the direction of the force

  8. Work and Energy…the motion (distance) is parallel to the direction of the force Garcon does work whenhe picks up the tray but not while he carries it around the room Garcon is not doing work

  9. Is Atlas doing work? • Atlas is staying in place • Atlas is not doing work

  10. Is work being done on the wall? • work may be done on the prisoner’s muscles …stretching, squeezing them, pumping the blood through the veins.. but this is not work being done on the wall • be clear where the work goes

  11. Is work being done?

  12. Example Problems How much work is done by a toy car with an applied force of 12 N which is moved for 39 m?

  13. Announcements • Notebooks due: • 1st & 2nd DUE WEDNESDAY • 3RD & 4TH DUE THURSDAY • 7TH & 8TH DUE FRIDAY • MAKE SURE TO HAVE ALL VOCABULARY AND WORK DONE BY THE TIME YOU TURN IT IN. • END OF SIX WEEKS NEXT WEEK • Three more grades going in – notebooks, lab, one pager

  14. Power

  15. Pit Pony

  16. A little bit of history • To find out how the power of his engine compared to that of a horse, James Watt measured how fast an average horse could do work. He found the answer and expressed the amount of work performed per second as a horsepower. • 1 horsepower = 746 Watts • A horse exerting 1 horsepower can raise 330 pounds of coal 100 feet in a minute. • In the US we rate engines in terms of horsepower (hP) and electricity in watts (kilowatts, megawatts)

  17. Horsepower

  18. Power • Power – the rate at which work is done. • Power = Work/time • Unit is Watt (joule/second)

  19. What can a more powerful engine do? One of 2 things Power = work done time 2x work or work time ½ time

  20. Example Problems If a 450 N boulder is dropped 2.4 m in 25 seconds, how much power is exerted on the object?

  21. The weight lifter used a force of 980 N to raise the barbell over her head in 5.21 seconds. Approximately how much power did she use while raising the barbell?

  22. Example Problems A mechanic used a hydraulic lift to raise a 12,054 N car 1.89 m above the floor of a garage. It took 4.75 s to raise the car. What was the power output of the lift?

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