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Spring force in SHM

  1. Sep 27, 2013 #1
    1. The problem statement, all variables and given/known data

    Answer the following question for a mass that is hanging on a spring and oscillating up and down with simple harmonic motion.

    2. Relevant equations

    Where in the motion is the magnitude of the force from the spring on the mass a maximum?

    3. The attempt at a solution

    I drew two free body diagrams for the oscillating mass: one at the positive amplitude, and one at the negative amplitude. At the positive amplitude, the spring force and the weight force, the only two forces acting on the mass, are pointed downward. At the negative amplitude, the spring force is in the positive direction (up the y-axis) and the weight force is in the negative direction. I believe the answer to this question is that the spring force will be maxed at the negative amplitude. I don't quite understand that. Since we're talking about magnitudes, shouldn't the spring forces be equal at the top and bottom of the oscillation? Isn't there some kind of symmetry?

    All help is appreciated.
  2. jcsd
  3. Sep 27, 2013 #2
    Where is the displacement maximum?
  4. Sep 27, 2013 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Of course. That's where the spring is stretched the most.

    Don't confuse the spring force with the net restoring force. There's also gravity to consider.
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