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Energy Mass equivilance

  1. Feb 5, 2010 #1
    This may have been hashed before, so forgive my indulgence if this post is a logical fallacy.

    Energy = Mass, OK

    Now it's stated that by increasing the temperature of a body the mass increases. I would derive this as the energy needed to raise the temp is transferred into the body.

    now the body with an increase in temp would be radiating this increase and thus also be reducing it's mass over a period of time, as the temp is reduced to pre-energy transference. Am I correct in this assumption?

    So is a nuclear reaction different? increasing the velocity of the particles to split the atomic structure requires energy and thus an increase in mass. I can't seem to find an agreed equivalence to this.

    Rest mass shouldn't apply to either case as the work or energy needed to increase the body temp is not at rest right?

    I'll state that I'm not formally educated in these fields so I'm sure most of the 'scribbly' writing goes over my head, however I can follow the process and interactions.
  2. jcsd
  3. Feb 5, 2010 #2
  4. Feb 5, 2010 #3


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    During fission, potential energy is being turned into kinetic energy. The total energy stays the same, and therefore the mass stays the same. If you eventually radiate away some energy as gamma rays, light, etc., then you end up with a lower mass.
  5. Feb 5, 2010 #4
    I'm sorry if it's confusing, It's a bit confusing to me as well.
    the term I believe is 'mass deficit' whereas the loss is in the form of heat, but isn't the process endothermic so that the splitting should increase the mass?

    and how does rest mass equate in the process if the process is most definitely not at rest?
  6. Feb 5, 2010 #5
    Okay, I was able to clear up my concept with some further reading.

    Here's the question, if a mass of x is increased in velocity it will according to E=Mc^2 increase in mass by the conversion factor of c^2. this would indicate a resistance to change and since the energy required to increase the velocity is proportional to the mass shouldn't we be able to measure the increase in mass at any velocity?

    When the accelerated mass slows down, does it conversely loose mass? how? if it it's converted heat then wouldn't the increase in velocity to nearby interactions due to the need to convert mass back to less mass also increase the mass of the excited nearby atoms? it seems to me that it becomes an fluxing wave of mass conversion up and down due to the always changing velocity of bodies.

    I wonder though if the original thought was that M=E/c^2 a relation to the available energy in a given mass and that the conversion of c^2 is in relation to SR and the limit of c. and then the velocity can be left out since it's not really the velocity of body but the energy mass equivalence. clear as mud right?

    Here's how this started in my head,
    I was lazily reading thru one of my Feynman books and came across the old light clock example for SR and time dilation etc.. Only this time I had the thought, this would make light an external frame of reference to everyone. that being the case what is lights frame of reference to everything else? and then what about red-shift? I thought the frequency of the light spectrum was the determining factor for the color. so how can the 'Doppler' effect be applied to light? from the above light clock example, if light is independent to any frame of reference how does this work?

    So the next thought was then if you were traveling at the speed of light you would not have a frame of reference to tell you so since light is still independent and the other outside frame would not be able to see you because his frame of reference can not account for mass or objects to be at the external frame of light. you'd be dimensionally not there in some way right?

    Okay maybe I should lay off the wine....good one to from Spain.

    Thanks for enduring my ramblings...
  7. Feb 5, 2010 #6


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    Not a direct answer to your question but here it is: the notion of an "increasing" mass is known as relativistic mass, and is by now almost a completely defunct concept. Almost everyone simply says that the kinetic energy (and momentum) or the body scale differently, and treats mass as a constant "invariant" mass.

    So you put energy in, KE increases. When you slow it down, KE decreases and there goes the energy. Much simpler way of thinking about things, I hope you see.
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