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Hypothetical Question involving Conservation of Energy

  1. Mar 3, 2008 #1
    I recently read a question in which a poster questioned what would happen if you dissolved a compressed spring in acid and an uncompressed spring in acid. The question was where would the stored energy go from the compressed spring as it dissolved? The answer was that in experiments scientists have found that as the compressed spring dissolved, the acid would heat up more than that of the uncompressed spring, conserving energy. I'd like to take a different approach.

    Let's say using nano-technology, we can build a spring one atom at a time. I wonder if it would take more energy to simply build a compressed spring than an uncompressed spring. If so, why? I know the answer is conservation of energy, but it is hard to imagine the atoms getting "harder" to put in place while making a compressed spring one atom at a time, but not for the uncompressed spring.

    Any thoughts?
     
  2. jcsd
  3. Mar 3, 2008 #2
    No thoughts. Sorry. Consider this thread and it will become obvious that "attaching one atom" would require more energy pressing it close. Because "attaching one atom" is nothing but a chemical reaction which results in a temporary equilibirum. Afterwards (according to your idea of "nanotechnology assembling") you would have to press the atom - or molecules respectively - closer together just as you would do with an already existant spring.
     
    Last edited: Mar 3, 2008
  4. Mar 3, 2008 #3
    I see it this way:
    The atoms want to be in certain places. (all the laws of QM, etc, it doesn't matter). When you make with nanotechnology the atoms closer then their equilibrium position, you need extra energy because you're placing them in a place that is not a minimum in energy.
     
  5. Mar 3, 2008 #4

    rcgldr

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    Potential energy isn't aways converted into actual energy due to destruction of the potential energy. As a better example, imagine burning a fully charged battery as opposed to burning a fully depeleted battery, is there any difference in the release of energy due to burning?
     
  6. Mar 3, 2008 #5
    If the eventual products of the burning are the same, then the charged battery will produce more energy if it burns. Of course some of the ingredients of some batteries won't burn at all, weather charged or not. in that case the potential energy will remain.
     
  7. Mar 3, 2008 #6

    rcgldr

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    I doubt this but for a simpler still example, imagine a piece of magnetic metal held some distance from an electromagnetice source. The metal has a potential energy based on it's position within the field. Now simply turn off the electromagnetic source. The potential energy is now zero.
     
  8. Mar 4, 2008 #7
    do you think energy isn't conserved in this case?
     
  9. Mar 5, 2008 #8

    rcgldr

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    No. Ignoring factors like heat energy, the magnetic particle has a total energy composed of the sum of it's kinetic and potential energy based on distance from an electro magnetic source in my example. However the potential energy depends on the existance of this magnetic field, which can simply be turned off. The kinetic energy would remain the same, but the potential energy would go to zero once the magnetic field was gone. Here the concept of total energy is partially depending on whether the electro magnetic field continues to exist.
     
    Last edited: Mar 5, 2008
  10. Mar 6, 2008 #9
    So Jeff if I read you right you dont completely buy the way energy is discussed in physics circles these days?
     
  11. Mar 6, 2008 #10

    rcgldr

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    I was referring to the specific case where potential energy of an object depends on the existance of a field that isn't permanent. If the field is altered or terminated, it obviously affects the potential energy of any object within this field. What laws of physics does this violate? I don't think that this violates the concept of conservation of energy.

    In the case of burning of a completely charged and a discharged battery, I'm not convinced that the difference in total energy output during the burning process is exactly identical to the difference in electrical potential energy difference between the batteries. What if only the pole areas of a fully charged battery are burned, turning them into insulators, rendering the battery useless, has this affected the potential energy of the battery?
     
    Last edited: Mar 6, 2008
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