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What's the work done moving an object up and then back down?

  1. Jul 3, 2015 #1
    If i lift it a distance x then bring it back down, so that the displacement is 0 but distance travelled is 2x.

    Will work done be doubled or will it be 0?
     
  2. jcsd
  3. Jul 3, 2015 #2
  4. Jul 3, 2015 #3
    Why is this so?
     
  5. Jul 3, 2015 #4
    What are your thoughts on this? How much work do you do on the weight while raising it? How much work do you do on the weight while allowing it to be lowered? What are the directions of the forces you apply while raising and lowering, and what are the corresponding directions of the displacements? How do the directions of the forces compare with the directions of the displacements?

    Chet
     
  6. Jul 3, 2015 #5
    I do the same work on raising and lowering the weight. My thought was that since a work is done to raise it up a distance x and then bring it down a distance x it should be doubled, however my father said that the displacement is overall 0 so the work it did was zero but I still cant understand why this is so.
     
  7. Jul 3, 2015 #6

    DaveC426913

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    Gold Member

    What is the definition of work?
     
  8. Jul 4, 2015 #7
    There are several different dictionary definitions of the word "work," and only one of these is the mathematically precise definition that physicists use to calculate the quantity they call "work." In physics, the work is positive if the force and the displacement are in the same direction, and negative if the force and displacement are in opposite directions. So, if you exert a force upward to move a weight upward, the work you do is positive. If you are exerting a force upward and the weight is moving downward, the work you do is negative (the weight is actually doing work on you). In both cases, according to a layman, you have done a net amount of work, but, according to the physicist's definition, the net amount of work you have done is zero.

    Chet
     
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