Work and Power
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Transcript of Work and Power
![Page 1: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/1.jpg)
Work and Power
![Page 2: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/2.jpg)
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
![Page 3: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/3.jpg)
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
![Page 4: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/4.jpg)
Work or no work?
![Page 5: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/5.jpg)
Work or no work?
Lifting a barbell over your head?
![Page 6: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/6.jpg)
Work or no work?
Holding a barbell over your head?
![Page 7: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/7.jpg)
Work or no work?
Is there work being done ON the tray?
![Page 8: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/8.jpg)
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?)
![Page 9: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/9.jpg)
WORK EQUATION:
• Work = Force x distance W = F x d
![Page 10: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/10.jpg)
• 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
![Page 11: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/11.jpg)
THINK!
• Remember the bus-pull challenge? At what point in this clip is work being done? Why?
![Page 12: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/12.jpg)
![Page 13: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/13.jpg)
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?
![Page 14: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/14.jpg)
• An apple weighing 1N falls a distance of 1m. How much work is done on the apple by the force of gravity?
![Page 15: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/15.jpg)
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?
![Page 16: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/16.jpg)
THINK!
• Does running up a flight of stairs require more work than walking? Why?
• What is the difference then?
![Page 17: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/17.jpg)
POWER
• POWER is how much work is done in a given time
POWER: the rate at which work is done or energy is converted.
– power = work / time P = W / t– Measured in watts (W)– 746 watts = 1 horsepower
![Page 18: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/18.jpg)
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?
![Page 19: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/19.jpg)
• 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?
![Page 20: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/20.jpg)
• On the bottom of your notes:
Using their scientific meanings, make a sentence using ‘work’ and a sentence using ‘power’.
![Page 21: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/21.jpg)
Exit Ticket #1-4
![Page 22: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/22.jpg)
1. What is the equation to find work?a. W=N x db.W=F x dc. W=N/dd.W=F/d
![Page 23: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/23.jpg)
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 Jb. 0.112 Nc. 1750 Jd. 1750 N
![Page 24: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/24.jpg)
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?
a. 5.55 Wb.5 Wc. 90 Wd.3.6 W
![Page 25: Work and Power](https://reader035.fdocuments.net/reader035/viewer/2022070502/5681387f550346895da031be/html5/thumbnails/25.jpg)
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.
a. 146 Wb.44.8 Wc. 173.8 Wd.7119 W