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Question: Particle speed & c

  1. Jun 26, 2009 #1
    Please, could someone here teach me, in a no-pun-intended crash course :smile:,
    of how relativity plays into the speed of electrons flying around an atomic nucleus
    as well as thermal energy vibrations.

    Ok - I know it's wrong to think like they did in the 19h century, making the analogy of electrons around atomic nuclei to planets revolving around a sun.

    Nevertheless, (average) particle speed is what temperature is.

    Also, I never understood: does the "speed" of electrons "flying around atomic nuclei" have anything to do with temperature? At sufficiently high temperatures, depending upon the element or compound, electrons do get stripped away from atomic nuclei. So, I assume a plasma is some sort of "soup" of electrons and atomic nuclei. Hence, it does not seem to me that there is any difference between temperature associated with electrons "flying around a nucleus" versus interatomic Brownian motion, since both contribute to the kinetic energy of the ensemble.

    Finally, the Nova program on the race for absolute zero asked if there is an "absolute hot".
    Wouldn't that be fixed by the "speed of light" of these electrons and nuclei?
  2. jcsd
  3. Jun 27, 2009 #2
    Temperature has nothing to do with the amount of energy --- it's the derivative of energy with respect to entropy. Indeed, the hottest possible temperature (in the sense that if you put anything in contact with it, the net energy flow will be outwards) is minus zero.

    The usual "speed=heat" is only true for a classical gas. Electrons around atoms are neither classical, nor a gas.
  4. Jun 27, 2009 #3
    I did not mean to make it sound like I believed that temperature is a "mass" quantity,
    that depends upon the total mass of a system. Of course, temp is a state quantity.

    Nevertheless, I don't see how temp has nothing to do with the amount of energy per unit mass. I know you did not say "per unit mass", but I infer you would have added that anyway.
  5. Jun 27, 2009 #4

    Vanadium 50

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    Absolutely untrue. Even in the case of gases, where this makes the most sense, it's not true. The average particle speed of a tank of hydrogen at 300K is not the same as the average particle speed of a tank of xenon at the same temperature.

    What you are describing is closer to heat than temperature.
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