The nature of heat

Discussion in 'Physics & Math' started by Magical Realist, Oct 31, 2015.

  1. Magical Realist Valued Senior Member

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    What is heat defined as? If it is the motion of molecules, how does it get transmitted from sunlight? How is heat contained in light at all? Is it related to wavelength? Or the energy of photons?
     
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  3. paddoboy Valued Senior Member

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    Heat is a form of energy. The more energy, the more heat.
    Heat is the transfer of energy between two systems as a result of a temperature difference by either conduction, convection or radiation.
     
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  5. Magical Realist Valued Senior Member

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    Heat is energy? That doesn't seem very specific. Radiation and electricity is energy too. What makes heat different?
     
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  7. paddoboy Valued Senior Member

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    Radiation and electricity are forms of energy that produce heat. There are many forms of energy.
     
  8. paddoboy Valued Senior Member

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  9. Magical Realist Valued Senior Member

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    So what distinguishes heat from electricity and radiation? Surely it has some unique characteristics that identify it as heat?
     
  10. danshawen Valued Senior Member

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    A match and a bonfire may burn at the same temperature, buy clearly the bonfire contains more heat. Heat is a form of bulk thermal kinetic energy.
     
  11. Q-reeus Banned Valued Senior Member

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    ????? Try again genius. Learn thermodynamics 101 before venturing out of your single-topic enthusiast comfort zone of GR/cosmology. Substituting either 'thermal current' or 'heat flow' at the start would be an improvement but still wouldn't cure the rest of that mixed up sentence.
     
  12. The God Valued Senior Member

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    Too many basics questions. Please go through below link, do not worry about number of pages, it will give you a fairly good idea and covers all your questions. As far as this thread is concerned, I expect huge copy pastes in multiple threads to prove the "genius definition of heat" and nature of heat etc..

    http://www.slideshare.net/krishnanunnimenon/the-nature-of-heat
     
    Last edited: Oct 31, 2015
  13. origin Heading towards oblivion Valued Senior Member

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    The simplist definition could be the transfer of energy between areas of different temperature. Heat always flows from hot to cold. Heat flows through conduction, convection and radiation.
    Temperature is a measrue of the motion (kenetic energy)of molecules, the transfer of that enegy from one molecule to another is heat (conduction). Photons of sunlight (primarily infrared) are absorbed by the electrons of the molecule increasing their
    kenetic energy (temperature). That is radiation heat transfer.
    There is no heat or temperature in sunlight. The energy of the photons transfers heat from the source of the photons to whatever material absorbs the photons. The shorter the wavelength the higher the energy of the photons so the higher energy transfer.
     
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  14. Kristoffer Giant Hyrax Valued Senior Member

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    "Genetic energy" was the best auto-correct (assume it was auto-correct) I've seen in ages.

    BTW I think it's kinetic.
     
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  15. origin Heading towards oblivion Valued Senior Member

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    Yeah, I wish my tablet wasn't so 'helpful'. Reminds me of the time a secretary sent out an email to the division discussing process engineers that she shortened to process engrs. She did not notice before she sent it that it auto corrected to process negros.
     
  16. Q-reeus Banned Valued Senior Member

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    No, paddoboy was not correct. A better shot would be a large-numbers statistical average energy owing to micro-scale incoherent radiation and/or random molecular or lattice KE, density of which (i.e. temperature) is an intensive and a scalar and does not imply or rely on any sense of vectorial energy flow. Heat within a perfectly evacuated hollow interior will be entirely radiant, but afaik there is never a case where it can be entirely owing to molecular or lattice KE.
    As per above, that covers one aspect, except 'random' should have been added there.
    Placing 'conduction' inside parentheses just confuses things, and even if not, still confuses heat with heat conduction.
    Sunlight photons are primarily in the optical band. If 'that portion of sunlight lying in the infrared spectrum' was meant, it should have been clearly stated. But I doubt it would be true in general anyhow.
    Radiant heat transfer is simply flow of radiation from A to B, period. Conversion from radiant to molecular or lattice thermal energy via absorption is a separate thing.
    Implying in general that energy radiated out from a hot body just disappears the instant it leaves the body. There is a distinction between 'color temperature' of thermal radiation (owing to its source), and its extant energy density, but there is always a useful notion of heat and temperature associated with thermal radiation.
     
    Last edited: Oct 31, 2015
  17. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Heat is thermal energy (in transit) - and EM radiation is a form of it.
     
  18. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Sorry, he was. You may be under the misunderstanding that heat is just thermal energy and doesn't need to be in transit. It's a common colloquial mis-statement (one I even use despite being a mechanical engineer specializing in HVAC!) probably because it is grammatically cumbersome when used properly, but it isn't actually correct.
     
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  19. paddoboy Valued Senior Member

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    Please Register or Log in to view the hidden image!

    My answer stands my genius friend!
    .Heat is the transfer of energy between two systems as a result of a temperature difference by either conduction, convection or radiation.

    Of course if you feel like elaborating instead of your childish dummy spitting, then go right ahead.
     
    Last edited: Oct 31, 2015
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  20. Magical Realist Valued Senior Member

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    So what property of photons allows them to transfer heat thru transparent space to matter itself? And how does the massless photon cause the molecules of matter it strikes to increase in kinetic energy? Wouldn't it need mass to induce movement?
     
  21. origin Heading towards oblivion Valued Senior Member

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    Geeze, relax. I think the explanation that I provided to MR was fine.
     
  22. Q-reeus Banned Valued Senior Member

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    Clearly you have 'mates' here who are prepared to wipe your backside. No 'spitting the dummy' - just trying to inject some precision into a very sloppy and opinionated thread. But hey, if 'majority wins' is the game here at SF, looks like I 'lose'. An amazing place is SF.
     
  23. paddoboy Valued Senior Member

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    No spitting the dummy aptly describes you at this time and considering the past thread you have had shifted to the fringes. I wouldn't be raising any precision aspect.

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