1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Work done by Spring

  1. Oct 7, 2008 #1
    1. The problem statement, all variables and given/known data
    Is the work done BY a spring always negative when you compress or stretch it?


    2. Relevant equations
    W=-1/2kx^2


    3. The attempt at a solution
    I know that the spring force always acts opposite of displacement when compressing or stretch. So when you compress or stretch the spring, the work the spring does should be -1/2kx^2. I'm having a hard time convincing myself mathematically though. So you compress the spring from x initial=0 m to a x final equal to some -4 m. The spring force according to this convention, F=-kx becomes a positive kx because the displacement is negative. When I integrate the force, do I put a a positive sign now, so in this case I would integrate the spring force from -4m to 0m? Also I know work is the Magnitude of the force times the Magnitude of the displacement for a constant force. Does this hold in varying forces such as the spring force?
     
  2. jcsd
  3. Oct 8, 2008 #2

    alphysicist

    User Avatar
    Homework Helper

    Hi rwx1606,

    This is true if the spring starts with x=0. So if the spring is initially unstretched (and uncompressed), then if it is stretched or compressed the work done by the spring is negative like you have.

    But if you talk about the the spring going from x=4 to x=2, for example, the work done by the spring force would be positive.

    The force is positive, but F is still F=-k x.

    No, you integrate to find the work done by the spring force. (If you try just multiplying the magnitudes, you'll find that you are missing a numerical factor.)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Work done by Spring
  1. Work Done by Spring (Replies: 3)

  2. Work done by a spring (Replies: 6)

Loading...