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[Work and Energy] Work positive or negative?

  1. Nov 24, 2009 #1
    1. The problem statement, all variables and given/known data
    I don't know when the work of a spring is negative, and when it's positive... When is the work of a spring negative and when is it positive?


    2. Relevant equations
    Wsp= -(1/2)(k)(xf2-xi2)

    3. The attempt at a solution
    I can get Wsp to be positive when the spring is stretch, but I want to know the theory behind it.
     
  2. jcsd
  3. Nov 24, 2009 #2
    When does a spring oppose motion?

    think about it in your everyday life pushing and pulling a spring
     
  4. Nov 24, 2009 #3

    rock.freak667

    User Avatar
    Homework Helper

    It's a sign convention. When a spring is compressed, something does work on the spring. So the work done by the spring is negative.

    When the spring stretches, the spring does work on the 'something', so the work done is positive.
     
  5. Nov 25, 2009 #4
    but negative work means opposing motion, therefore the spring always does negative work
     
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