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Difference between heat and temperature

  1. Aug 15, 2012 #1
    I know there is a difference between heat and temperature as once I was told what it is. I remember it being very subtle and that's probably why I cannot remember the details anymore. Would anybody be so kind as to refresh my memory?
     
  2. jcsd
  3. Aug 15, 2012 #2
    Yes. Temperature is a quantitative measure of a material's thermal energy. Heat is the transfer of thermal (internal) energy between materials.
     
  4. Aug 15, 2012 #3

    berkeman

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    There is a good PF Library entry about Heat by user Hootenanny:

    https://www.physicsforums.com/library.php?do=view_item&itemid=121

    .
     
  5. Aug 16, 2012 #4
    cheers
     
  6. Aug 16, 2012 #5
    This isn't the way heat is described in introductory textbooks on physics. However, the following picture has helped me do thermodynamics problems with mathematics. If you are entering an advanced class in physics, maybe telling you this heuristic model will help more than refreshing your memory.
    There is a fluid like quantity called entropy. It isn't a "real" fluid. On a microscopic scale, entropy is the same as disorder. However, entropy behaves like a indestructible fluid on a macroscopic scale. The unit of entropy is an energy unit divided by a time unit.
    With the fluid properties of entropy in mind:
    The word "heat" often refers to the entropy of a system.
    Sometimes, the word "heat" refers to the energy carried by a flow of entropy rather than the entropy itself. In this case, the heat is measured in units of energy.
    "Temperature" is the pressure that the entropy is under. Like a fluid spontaneously flows from high pressure to low pressure, entropy spontaneously flows from high temperature to low temperature. "Temperature" is in units of degrees, but really refers to a type of entropy pressure.
    If it confuses you, ignore it.
     
  7. Aug 16, 2012 #6

    Vanadium 50

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    You can stick your hand in a 400 degree oven with no ill effects. That's not true if you stick it in a pot of boiling water. The water has more heat, although the air in the oven has a higher temperature.
     
  8. Aug 17, 2012 #7

    davenn

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    Yes agreed

    is that just a case of the water being more efficient at conducting the heat to the hand
    than the air is ?

    After all they say air is a poor conductor of heat

    Just wondering :)

    Dave
     
  9. Aug 17, 2012 #8

    haruspex

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    The most obvious difference is that temperature is an intensive property and heat is an extensive one. That is, if you have twice as much material at the same temperature it holds twice the heat.
    You could get past that by changing your question to be the difference between temperature and heat per unit of substance (mass, volume, whatever...). In fact, temperature is a measure of heat energy per something, but the something is a little unusual - it's state. In an ideal gas, for example, there can be several states per molecule. For a monatomic gas, there are three energy states - velocities in the 3 dimensions. A diatomic gas also has spin about two axes, making 5 states. For statistical reasons, each state tends to have the same average energy, so a diatomic gas holds more heat energy than the same number of molecules of a monatomic gas at the same temperature.
     
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