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If the clamped spring is dissolved in acid what becomes of its potential energy?

  1. May 18, 2010 #1
    If a compressible metal spring is compressed it achieves potential energy. But if the spring is dissolved in acid at its clamped state where does the stored potential energy go? Or what becomes of its potential energy.

    Help me please.
     
  2. jcsd
  3. May 18, 2010 #2

    phyzguy

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    Science Advisor

    I think what would happen is that as the spring dissolved, eventually it would lose its structural integrity and the pieces of the spring would fly apart. The moving pieces would have kinetic energy equal to the stored potential energy of the spring. The pieces would then be stopped by friction in the acid, so ultimately all of the stored potential energy would go into heating up the acid.
     
  4. May 18, 2010 #3

    Dale

    Staff: Mentor

    A piece of metal under strain has a different electrochemical potential than an identical piece of unstrained metal. So that leads to slightly faster corrosion with higher currents and greater heating of the electrolyte.
     
  5. May 18, 2010 #4
    there you go its true.
    the spring would first at most probably the point with greatest stress(midpoint) and then PE "stored" woul go inot heat,sound, and KE which is dissipated most of the PE is lost barely any is used for the reaction.
     
  6. May 19, 2010 #5
    Thank you for your support. I somehow got it.
     
  7. May 21, 2010 #6
    What if the spring was encapsulated in some sort of container that would prevent it from expanding in any direction - but this container was unaffected by the acid in question - even though it had holes in it to allow the acid to reach the spring?
     
  8. May 21, 2010 #7
    Still its simple, since the spring is not stretched it will begin to dissolve as a whole rupturing arbitrarily, and slowy, because the energy if the system is maintained constant, there being no external parameters involved (as an assumption). so the spring will dissolve but rupturing very slowly so that change in KE=0 to maintain the condition you presented.
     
  9. May 22, 2010 #8
    But if the spring volume has no room to expand, what happens to the kinetic energy stored as potential as it dissolves?
     
  10. May 22, 2010 #9

    Dale

    Staff: Mentor

    I answered that in post 3. Even if the spring does not break there is extra energy given to the electrolyte by a material corroding under strain.
     
  11. May 22, 2010 #10
    So the compression of the spring contributes to the total chemical potential of the reactive substances? Mechanical energy can simply become chemical energy because the reaction is taking place under strain?
     
  12. May 22, 2010 #11

    Dale

    Staff: Mentor

    Yes. Even without the spring breaking.
     
  13. May 22, 2010 #12
    Are you sure the mechanical energy of the spring wouldn't create turbulence by pressing against the sides of the container while breaking apart inside? I don't think that mechanical energy can be converted into chemical energy except by changing parameters of the reaction such as temperature and pressure of the system.
     
  14. May 22, 2010 #13

    Dale

    Staff: Mentor

    Certainly it would, but this does not answer the conservation of energy question alone. As soon as any of the spring is dissolved the spring constant is reduced and therefore the mechanical potential energy is reduced. If the spring breaks only this reduced amuont of energy is recovered. You cannot explain the conservation only by the spring breaking.

    And changing temperature and pressure can cause a chemical reaction to shift equilibrium thereby storing chemical potential energy.
     
  15. May 22, 2010 #14
    I would think the amount of wave-energy dispersed as turbulence would be equal to the amount potential in the compressed spring. The spring wouldn't appear to expand because it was incapsulated, but while dissolving it would vibrate, and the vibrations would travel through the container and into the surrounding liquid. The only way it would raise the pressure or temperature of the system is if the system was completely insulated, in which case I would guess the waves would become heat since both are KE.

    How would that be relevant?
     
  16. May 22, 2010 #15

    Dale

    Staff: Mentor

    Sorry, I didn't realize you were still talking about th "encapsulated spring" scenario. In that case there would be no turbulence at all. A mechanical failure of the spring would turn the remaining mechanical potential energy into mechanical waves which would heat up the electrolyte, but again, you cannot account for all of the energy unless you consider the chemical energy.

    I was just providing a counter example to your suggestion that mechanical energy cannot be converted into chemical energy. That was wrong, chemical energy can be converted into mechanical energy and vice versa.
     
  17. May 22, 2010 #16
    What scenario were you addressing then?
    What other form does mechanical energy in a liquid take except turbulence? How would mechanical energy immediately become heat, without first becoming waves/turbulence in the liquid?

    Any form of energy can be converted into any other form. The issue is what route it takes.
     
  18. May 22, 2010 #17
    the crux here is that there will be not net change in the system+surroundings energy content,the following transforms occur______
    PE---->KE...under strain
    PE/KE----> chemical energy(very small part) + heat(non-frictional+frictional).....under strain/after rupture respectively.
    a part of non frictional heat is lost directly to the surrounding and a part heats the spring substance up and so is a pat of frictional heat
    HEAT---> chemical energy the kinetics of the reaction are disturbed.
    did i miss anything out..?
    *all energy changes are subject o various coefficients hence most of the energy is use to cause a temperature change.
     
  19. May 23, 2010 #18

    Dale

    Staff: Mentor

    The original one. The compressed spring in a corrosive liquid (no spring encapsulation). In that scenario when the spring fails the pieces will go shooting around inside the liquid and there will likely be turbulent flow.

    In the scenario with an encapsulated spring the encapsulation prevents the pieces from shooting around the liquid, so there will be waves and probably friction, but probably not turbulence.

    Both mechanical waves and laminar flow are other forms of mechanical energy in a fluid that can dissipate into heat without ever becoming turbulent. The word turbulence refers to a specific regime of flow.
     
  20. May 23, 2010 #19
    I didn't know of a more general word to refer to wave energy in a fluid at a super-molecular level.
     
  21. May 23, 2010 #20
    Sorry, i forgot the turbulence.
    please stop complicating the picture, the guy's got it in the first few threads.
     
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