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Work, Power, and Efficiency

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Work, Power, and Efficiency Work is the transfer of energy that results from applying a force over a distance if nothing moves, no work was done unit of measurement ... – PowerPoint PPT presentation

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Title: Work, Power, and Efficiency


1
Work, Power, and Efficiency
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Work
  • is the transfer of energy that results from
    applying a force over a distance
  • if nothing moves, no work was done
  • unit of measurement is the Joule (J)
  • used to be a Newton-meter (Nm)
  • (this is about equal to lifting quarter pounder
    up 3 ft in a second)
  • http//www.youtube.com/watch?vIvcOYOO0Fvw

4
Work formula
W F D
W work F force D distance
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Example problem
  • How much work is done when an object with a force
    of 60 Newtons is moved a distance of 7 meters?

given formula
set up problem answer w/ unit of
measurement
F 60 N WFD 60N(7m)
420 Joules D 7 m
8
  • There are different ways to get work done, but
    regardless, the work must be done.
  • Work Force x Distance
  • Work Force x Distance

9
What is the difference?
3 m
3 m
10
Power
  • how fast work is being done
  • unit of measurement is the watt (W)
  • James Watt, a Scottish engineer, invented the
    steam engine.
  • James Watt explained power as the number of
    horses his engine could replace
  • large quantities of power are measured in
    kilowatts (kW)
  • 1000 W 1 kW
  • Americans often use horsepower
  • 1 horsepower 746 watts

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Power formula
P W/T
P power W work T time
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Example problem
  • A motor does 500 Joules of work in 5 seconds.
    How much power does the motor have?

given formula
set up problem answer w/ unit of
measurement
W 500 J PW/T 500 J / 5 sec.
100 watts T 5 sec.
16
Efficiency
  • the comparison of work put into a machine to the
    work you get out of the machine.
  • Work input (WI ) is the work that goes into a
    machine
  • Work output (WO ) is the work done by a machine
    or the work you get out of the machine
  • machines are always less than 100 efficient
    because of friction
  • however, they still help us by often reducing the
    amount of force we put in by increasing the
    distance we put in

17
Efficiency formula
Efficiency WO (100) WI
E Efficiency WO Work Output WI Work Input
18
Example problem
  • What is the efficiency of a machine that produces
    150 Joules of work when 160 Joules of work is put
    into it?

given formula
set up problem answer w/ unit
of measurement
WO 150J E WO(100) 150J/160J(100)
94 WI 160J WI
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