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Work and Power

Work and Power. Objectives:. Define work and power Calculate work done on an object and the rate at which work is done Use ‘work’ and ‘power’ as science terms. Work and Power notes:. In science, ‘work’ has a specific meaning

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Work and Power

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  1. Work and Power

  2. Objectives: • Define work and power • Calculate work done on an object and the rate at which work is done • Use ‘work’ and ‘power’ as science terms

  3. Work and Power notes: • In science, ‘work’ has a specific meaning • Work is ONLY done when a force causes a change in the position or motion of an object in the direction of the applied force • i.e. making something move because of force

  4. Work or no work?

  5. Work or no work? Lifting a barbell over your head?

  6. Work or no work? Holding a barbell over your head?

  7. Work or no work? Is there work being done ON the tray?

  8. THINK! • What’s the difference between doing work and not doing work? • How do you think you might calculate ‘work’? (Hint: what HAS to happen for work to be done?)

  9. WORK EQUATION: • Work = Force x distance W = F xd

  10. Work is measured in joules (J). • 1 J = 1 N•m = 1 kg•m2/s2 • 1 joule is roughly equal to the energy required to lift a small apple 1 meter *N measures force/weight *m measures mass... To find weight in N, need to use w=mg James Prescott Joule

  11. THINK! • At what point in this clip is work being done? Why?

  12. Practice: • A crane uses an average force of 5200 N to lift a crate 25 m. How much work does the crane do on the crate?

  13. An apple weighing 1N falls a distance of 1m. How much work is done on the apple by the force of gravity?

  14. Challenge! • A mechanic uses a hydraulic lift to raise a 1200 kg car 0.5 m off the ground. How much work does the lift do on the car?

  15. THINK! • Does running up a flight of stairs require more work than walking? Why? • What is the difference then?

  16. POWER • POWER is how much work is done in a given time POWER: the rate at which work is doneorenergy is converted. • power = work / time P = W / t • Measured in watts (W) • 746 watts = 1 horsepower

  17. Practice • While rowing across the lake during a race, John does 3960 J of work on the oars in 60.0 s. What is his power output in watts?

  18. Using a jack, a mechanic does 5350 J of work to lift a car 0.500 m in 50.0 s. What is the mechanic’s power output?

  19. On the bottom of your notes: Using their scientific meanings, make a sentence using ‘work’ and a sentence using ‘power’.

  20. Exit Ticket #1-4

  21. 1. What is the equation to find work? • W=N xd • W=F xd • W=N/d • W=F/d

  22. 2. The brakes on a bicycle apply 125 N of frictional force to the wheels as the bicycle travels 14.0 m. How much work have the brakes done on the bicycle? a. 8.9 J b. 0.112 N c. 1750 J d. 1750 N

  23. 3. It takes 100 J or work to lift a box 18 m. If this is done in 20 s, what is the power output? • 5.55 W • 5 W • 90 W • 3.6 W

  24. 4. Anna walks up the stairs on her way to class. She weighs 565 N and the stairs go up 3.25 m vertically. calculate her power output if she climbs the stairs in 12.6 s. • 146 W • 44.8 W • 173.8 W • 7119 W

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