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Energy of a melted spring

  1. Apr 26, 2012 #1
    So I've bounced this question off a few physicists that I respect highly - my professors, and even a founding member of the Perimeter Institute here in Canada. None of them had a definite answer, however.

    My question is this: What happens to the stored elastic potential* energy of a spring or likewise object when you change its chemical properties by melting it? How is the energy transferred? Does it matter if the spring is compressed, or stretched?

    If anybody here has a theory, I am very curious to hear from you.
     
  2. jcsd
  3. Apr 26, 2012 #2

    mfb

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    The compression/extension changes distances between atoms/molecules and therefore adds potential energy to their positions.
    My guess: I would expect that this energy is released as thermal energy as soon as the integrity of the material begins to break down.
    In addition, I would expect that your stressed material gets weaker at slightly lower temperatures.
     
  4. Apr 26, 2012 #3

    Janus

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    The material of the spring has a "heat of Fusion". This is the energy that it takes to cause it to go from solid to liquid while not raising the temperature of the material.

    For instance, for ice/water it is 334 J/g. It would take 334 Joules of energy to turn 1 gram of 0°C ice into 1 gram of 0°C water.

    It is the energy needed to break the bonds holding the atoms in place. When you stretch or compress a spring, you are putting stress on those bonds. (too much stress will permanently deform or break the spring)

    When you heat the spring, the increased vibration of the atoms also put stress on the bonds.

    If you heat a spring under tension, you are adding to stress that is already there. The end result is that the bonds will break sooner than they would otherwise. The energy stored in the bounds just goes to reducing the energy needed to melt the spring. It reduces the heat of fusion.

    Thus if you had a spring storing 10 joules of energy, it would take 10 joules less energy to melt the spring than it would if the spring stored zero energy.
     
  5. Apr 26, 2012 #4
    This makes enough sense, but what about a similar situation?

    Let's say in deep space, you have two magnets. They are initially stuck to each other (north to south). You then spend X amount of energy to pull one of the magnets *very* far away.

    You then melt the remaining magnet, thus eliminating its magnetic characteristics. What happens to the X amount of energy that was stored in the magnetic system?
     
  6. Apr 27, 2012 #5
    Changes in magnetic feilds give off electromagnetic waves, e.g. light.
     
  7. Apr 27, 2012 #6

    mfb

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    Insignificant, if you don't rip the magnets apart with a speed comparable to the speed of light.

    The initial magnets have a binding energy compared to the "free" state, which is given by the smaller energy stored in the (combined) magnetic field.

    In a ferromagnetic material, I think the lowest energy state is a net field of 0 with many small magnetic domains inside and nearly no field outside. If you have a global field from the material, you have energy which can be set free by melting the stuff.


    Edit@Khashishi: Oh thanks, I forgot about that part.
     
    Last edited: Apr 27, 2012
  8. Apr 27, 2012 #7
    It takes some heat to change from the ferromagnetic phase to the nonmagnetic phase. As you apply heat, the temperature rises until it hits the Curie point, and then it stops rising until the magnetic domains "melt". It takes more heat to "melt" the magnets when they are together than apart, because you have to overcome the energy of interaction between the magnets.
     
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