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Non-linear system

  1. Nov 17, 2014 #1
    1. The problem statement, all variables and given/known data
    In this question we will consider a damped mass-on-a-spring system whose spring exhibits cubic deviations from Hooke’s law. We will consider a damped spring with a restoring force F such that


    where β is the “Hookian” part and α is a new nonlinear term. Unlike the usual spring constant k, β can have either sign. Use γ (not 2γ) as the damping parameter that multiplies x'.

    1.) What does the potential energy function look like for this system? Consider cases where α and β are both positive and negative.
    2.)Solve for the fixed points of this system and determine how their stability depends on α and β.

    3. The attempt at a solution

    So the general equation of motion with damping and restoring force is: x'' + γx' + βx + αx^3 = 0
    So I know the net force is F = -γx' - mβx - mαx^3. And in general F = - dU/dx (however this is true for conservative forces -hence I don't think it would apply here). So can I just integrate the for the Force? If not, I unsure how to approach this problem to get the potential energy function.
  2. jcsd
  3. Nov 17, 2014 #2


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    Homework Helper

    The restoring force has potential that you can find by integrating the restoring force.
    Last edited: Nov 17, 2014
  4. Dec 3, 2014 #3
    So then I was wondering, if I had to determine the fixed points of the system would setting the restoring force equal to zero and solving be sufficient ?
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