14 1 Work And Power
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14 1 Work And Power






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14 1 Work And Power 14 1 Work And Power Presentation Transcript

  • 14.1 Work and Power When Does a Force Do Work? How Are Work and Power Related?
  • What is Work?
    • Work is the product of force and distance
    • For a force to do work on an object
    • Some force must act in the same direction as the object moves.
    • No movement = No work done
    • Work requires motion
  • Work Depends on Direction
    • Any part of force that does not act in the direction of motion 
    • Does no work on an object
    • Work = Force X Distance
    • Units of work = Joule
    • Derived unit of Newton x Meter (N x m)
    • (Name after James Prescott Joule 1818-1889)
  • What Is Power?
    • Power = is the rate of doing work.
    • Doing work at a faster rate requires more power.
    • Increasing your power increases amount of work done in a given time.
  • Examples of Power
    • Ex. Using a Snow blower compared to shoveling a walkway… Which is faster?
    • The size of engine used by a machine indicates its power.
  • Calculate Power!
    • Calculate Power:
    • Power = Work / Time
    • Units for Power = Watt (W)
    • 40-watt light bulb requires 40 joules each second that it is lit.
    • The same amount of energy is used to raise your book 1 meter high in half a second
  • James Watt and Horsepower
    • Horsepower is another unit of power
    • Horsepower (hp) is = to 746 watts
    • James Watt first defined
    • Watt was looking for a comparison for the steam engines he had invented.
    • Used horse as they were used most in the 1700s
  • James Watt and Horsepower
    • Defined the Horsepower based on the power output of a very strong horse.
    • Ex. If you have a 4hp Rototiller it would get as much work done as a plow pulled by 4 horses.