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A few Questions On Heat

  1. Mar 17, 2009 #1
    If heat has three forms ,radiation, convection and conduction, isnt convection another form of conduction? The heat is still moving through the vibration of the atoms convection would just be the pattern at which it is moving in. Another question is how does the heat from the sun radiate to earth?
  2. jcsd
  3. Mar 17, 2009 #2
    Heat doesn't have three forms. Radiation, convection and conduction are ways in which heat is transferred.

    As for your second question I think you've already answered it. There are three ways heat is transferred: radiation, convection, and conduction. Well what did you say the sun does? It radiates heat, get it?
  4. Mar 17, 2009 #3


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    Convection involves hot fluid motion on a macroscopic scale (air or water currents). Conduction involves molecular vibration transmitting energy by interactions within the material (usually solid). Radiation heat transfer is by photons going from hot body (such as sun) to cooler body (such as earth).
  5. Mar 17, 2009 #4
    The pattern makes all the difference. Specifically convection occurs due to fluid velocities which is what is left over after a sort of macroscopic averaging over microscopic movements in a volume that is small compared to the system size but still large compared to the atomic size, while conduction is entirely due to those microscopic movements that convection averages away.

    To be totally pedantic, radiation, convection, and conduction are three ways of 'doing heat on a thermal system' (compare with 'doing work on a mechanical system').
  6. Mar 17, 2009 #5


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    Staff: Mentor

    For a very nice PF Library entry on Heat, click on the underlined "heat" word in the original post.
  7. Mar 17, 2009 #6
    Just some added thoughts already expressed:

    Conduction and convection requires some form of medium; be it air, water, metal, etc...

    Radiation is different. A specific physical medium is not required. It can occur in a complete vacuum, for example.
  8. Mar 17, 2009 #7
    To simplify greatly, in convection atoms move about and take their heat energy with them. In conduction atoms vibrate and collide with other atoms transferring kinetic energy to them, which is what thermal energy really is. In radiation atoms emit photons which travel outward at c until the collide with something else and then add energy to it.

    Edit: Thanks mathman, fixed it.
    Last edited: Mar 18, 2009
  9. Mar 18, 2009 #8


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    I think you meant to say convention in the first sentence.
  10. Mar 28, 2009 #9
    I think you meant to say convection. :)
  11. Mar 28, 2009 #10
    Don't forget evaporation etc.
  12. Mar 28, 2009 #11


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    You say that with such conviction. :biggrin:
  13. Mar 28, 2009 #12
    Let's not make this into a huge conniption. :tongue2:
  14. Mar 28, 2009 #13
    Hey, that was my 100th post!

    Good thing I didn't waste it...
  15. Mar 28, 2009 #14
    Is evaporation a kind of convection? If I threw a dollop of molten lead into a vat of water to warm it up, wouldn't that be convection, too?
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