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Homework Help: Force and energy

  1. Mar 8, 2009 #1
    If I have a energy of a particle and I need to calculate the expression for force on it how do i do it.

    eg: energy of a spring = k*(|x1-x2| - L )^2

    where x1 and x2 are particle at end of the springs and K is stiffness. L rest length.
  2. jcsd
  3. Mar 9, 2009 #2
    I think it is better to start with
    internal force=-d(potential energy)/dx
    potential energy=kxx/2
    internal elastic force -kx
    In the gravitational field
    Energy mgx
    Force -mg
  4. Mar 9, 2009 #3
    Thanks bernhard. What i was wondering is if it is more complicated force like rod bending where energy is given by E = k (theta - original theta)
    and new theta is given by tan(inverse) [ (x1-x2)x(x2-x3)/(x1-x2).(x2-x3))]
    x -> cross prdt
    . -> dot prdt

    and X1 and X2 are joined with a rod. and X2 and X3 re joined with a rod. K is stiffness
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