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Perpetual Motion within an atom?

  1. Apr 27, 2005 #1
    [SOLVED] Perpetual Motion within an atom?

    I have something to add to this. Since I don't quite understand what the guy above said I'm sorry if I repeat a question of his.
    If electrons are goin' around an atom with a balance of kinetic and Potential energy, and they've been spinning since the dawn of time, doesn't that entail perpetual motion? I doubt thay've slowed down any since ther is nothing for them to friction against like in our everyday lives.
    I've even asked my physics teacher and he didn't know. (I'm in High School) Then again this is a bit out of his scope I think...
  2. jcsd
  3. Apr 27, 2005 #2
    Really ???

    First of all, atoms (like we know then 'today') have not existed from the very first moments of the big bang because there was too much thermal energy to actually form atoms.

    Secondly, electrons do NOT orbit the nucleus in circles. That is the Bohr-model which is a very rude approximation/simplification of reality, yet it does a very good job at describing the most abundant atoms that we know : the H-atom. Besides, QM teaches us that we have a certain probability to find electrons in the orbitals. For example the s-orbital has spherical symmetry which implies that the electron really is everywhere around the atomic nucleus, prior to any measurement.

    Thirdly, electrons have an intrinsic quantum number called spin, but that does not imply that they actually orbit their axis, because they do NOT.

    Finally, for atoms to 'arise' their must be some energy available. One of the most famous laws is physics is conservation of total energy. This means that in processes the total energy must be the same when you compare the initial and the final state.

  4. Apr 27, 2005 #3


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    Good question.

    There is also a saying that an object, once in motion, remains in motion. There is nothing inherently wrong with perpetual motion in that sense anyway. The second law of thermodynamics - the one that says you cannot construct a perpetual motion machine (PMM) - covers the critical detail of this: you cannot extract work from a PMM.

    So in your analogy, you cannot extract energy from an atom while leaving it in its original state.
  5. Apr 28, 2005 #4
    No friggin' duh! I'm not that stupid.

  6. Apr 28, 2005 #5
    Do you even understand the actual question that you asked ?

    duhh :rolleyes:

  7. Apr 28, 2005 #6

    Meir Achuz

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    Don't browbeat so much.
  8. Apr 28, 2005 #7
    browbeat, that's a word i did not know. I looked it up in the dictionary...Thanks Meir, for enlarging my English vocabulary.

    besides, may i ask what country you are from. Is it Isreal ?

  9. Apr 29, 2005 #8
    Doesn't thermodynamics deal with macroscopic systems wich are build of zillion components?
    Thermodynamics first law (conservation of energy) seems to be true for any physical system, but second law actually deals with quantities like entropy and temperature, wich are innerently related to systems with many, many components, I don't think it can be applied to a system with only a bunch of constituent parts, like an atom.
    In other words, I think a system with only 2 components, like the hydrogen atom, is certainly not claiming to be studied with statistical mechanics.

    What do you people think?
    (Actually, my knowledge in thermodynamics is very rusted, and I admit I could be plain wrong with my argument. I'd really like to have some confirmation...).
  10. Apr 29, 2005 #9
    heres a great web page giving all the specifics on the Bohr ModelBohr model
    I know that every atom has its own unique orbit of electrons pertaining to its elements but Atoms have different energy states such as "ground and excited states" in order for the atom to switch from different energy levels it needs I believe a photon that matches one of the exact energy levels of the orbits of the electrons..anyhow hope it helps some :smile:
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