14 1 Work And Power

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14 1 Work And Power

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

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