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Work and spring

  1. Oct 17, 2012 #1
    does spring always do negative work?

    how could it do positive work?

    I can't think of any situation
     
  2. jcsd
  3. Oct 17, 2012 #2

    cepheid

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    Really?

    Suppose you have a spring with a mass at the end of it. The spring is compressed, because you are pushing on the mass and holding it there. Then you release it. The restoring force acts to extend the spring, pushing the mass outward along with it. The displacement of the mass is in the same direction as the force. Therefore, the force does positive work. You *know* that it has done positive work, because the kinetic energy of the mass has increased.

    It's only once the spring extension goes past the equilibrium position, and the spring becomes stretched, that the restoring force switches sign and starts to pull the thing back.
     
  4. Oct 17, 2012 #3
    Thank you so much :D
     
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