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I If something moves fast it gains temperature?

  1. Sep 18, 2016 #1
    Temperature is the average of the kinetic energy of the particles, if the bunch of particle moves fast and you look at the particles in two differece frame of reference, on steady with the bunch of particles and the other not, in the last one you get an higher temperature of the bunch of particle? If not why?

    And again, since a body emits electromagnetic radiation at a certain temperature, if you see that body in different frame of reference you should get a doppler effect right? So if you attend to measure the temperature considering the light emmited you get different values?
  2. jcsd
  3. Sep 18, 2016 #2


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    Staff: Mentor

    It is the average kinetic energy of the individual particles using a frame in which the system whose temperature is being measured is at rest. Thus
    You do not, because the the "extra" kinetic energy from choosing a frame in which the system as a whole is moving does not count towards the calculation of the temperature.

    This will look much less arbitrary and will make more sense if you learn the definition of temperature from statistical mechanics, where the temperature is calculated from the relationship between the change of energy of a system and the number of microstates available to it. The "average kinetic energy" understanding of temperature is derived from this calculation.
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