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Power. Work has to do with a force causing a displacement . It has nothing to do with the amount of time that this force takes to cause the displacement. Consider a rock climber… he may ascend a few meters very slowly.

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Power

Power


Power

  • Work has to do with a force causing a displacement.

  • It has nothing to do with the amount of time that this force takes to cause the displacement.


Power

  • Consider a rock climber… he may ascend a few meters very slowly.

  • A hiker can ascend the same height in far less time by taking the easier path.

  • They do the same amount of work, but the hiker does it much quicker.


Power

  • The amount of work done over time is called power.

  • The hiker has a better power

    rating than the rock climber.


Power

P = W/t

P- Power

W- Work

t- time


Power

  • W= Fd (when force and displacement vectors are in the same direction)

  • P= W/t

  • P= Fd/t

  • d/t = v

    So………

    P =Fv


Power

  • Unit of measurement for power: the Watt (W).

  • 1 Watt = 1 J/s = 1 kg m2/s3

  • Named after James Watt (b. 1736), an engineer whose improvements to the steam engine were very important to the Industrial Revolution.


Power

James Watt (Scottish)


Power

  • You often see power measure in horsepower

  • 1 horsepower (hp) = 746 W

  • The term was adopted in the late 18th century by James Watt to compare the output of steam engines with the power of draft horses


Power

  • Machines, people, animals, etc. all have power ratings.

  • I.e., the amount of work over time. More work over less time means a higher power rating.


Example

Example

  • A 70 kg jogger runs up a long flight of stairs in 4.0 s. The vertical height of the stairs is 4.5 m. Estimate the jogger’s power output in both watts and horsepower.


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