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Do heat will flow from the lower energy to higher

  1. Sep 16, 2006 #1
    do heat will flow from the lower energy to higher/
     
  2. jcsd
  3. Sep 16, 2006 #2

    Hootenanny

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    Heat is the transfer of energy. The second law of thermodynamics states that the entropy of an isolated system not at equilibrium will tend to increase over time, approaching a maximum value. Which basically means that heat cannot pass from a colder object to a hotter object without work being done.
     
  4. Sep 16, 2006 #3

    SGT

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    Yes, energy depends on temperature and on mass, so a large cold mass has more energy than a small hot one.
    An iceberg has much more energy than a bucket of boiling water. If you throw the water in the bucket on the iceberg, energy will flow from lower to higher.
     
  5. Sep 16, 2006 #4
    how does something cold have more energy than something hot? isn't t heat a form of energy?
     
  6. Sep 16, 2006 #5
    This is because the cold object has a much bigger mass than the hot object.
    We should think heat as the energy of transfer
     
  7. Sep 16, 2006 #6

    Andrew Mason

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    This may be true, but the quantity of energy does not determine how heat will flow. How about an iceberg at absolute 0? The boiling water in the bucket has much more energy than such an iceberg and heat still flows from the boiling water to the iceberg.

    It is the temperature of the two masses which determines the direction of heat flow. Heat energy will only flow directly from hot to cold. It will never flow directly from cold to hot.

    AM
     
  8. Sep 17, 2006 #7

    SGT

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    I am talking of a real iceberg, whose surface temperature should be around 240K or more and a mass of sevral million tons. It certainly has greater energy than the bucket.
     
  9. Sep 17, 2006 #8

    Doc Al

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    I hope you realize that (as AM explained) "heat" naturally flows from hotter to colder (based on a difference in temperature, not total energy content).

    If you think otherwise, then perhaps you think that if you rest a bucket of water on a big enough iceberg it will come to a boil?
     
  10. Sep 17, 2006 #9

    SGT

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    What I said is that the iceberg contains more energy than the bucket, but heat will flow from the hot, less energectic bucket to the cold, more energectic iceberg.
     
  11. Sep 17, 2006 #10
    Heat itself, its essence and quiddity is motion and nothing else.

    We don't talk about motion flowing from areas of high motion to areas of low motion. Instead we apply labels like heat and energy, and happily talk about them flowing instead.
     
  12. Sep 19, 2006 #11
    0th law of thermodynamics: thermal energy flows from hotter to colder, and eventually reaching an equilibrium in a closed system.
    hotter: molecules vibrates/travels faster
    colder: molecules vibrates/travels slower
    energy flow/transfer: faster molecules collide with slower molecules, faster molecules slow down, slow molecules speed up, finally reaching the same speed (momentum? KE?)
     
  13. Sep 19, 2006 #12

    HallsofIvy

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    Yes, that was the whole point. The original question was whether heat could flow from a lower energy object to a lower energy object. Because heat flow depends on temperature, not energy, the answer is yes. A large object, such as an iceburg, can have lower temperature than a small object, such as a boat, so that heat will flow from the boat to the iceburg but the iceburg has greater total energy than the boat.
     
  14. Sep 19, 2006 #13

    Doc Al

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    Andrew's comment was a response to SGT's comment, which could have been clearer. The OP asked "Does heat flow from low energy to higher?". I think SGT read that question as meaning "Is it possible for heat to flow from low energy to high energy?"

    A clearer answer might have been: "The direction of heat flow depends on temperature difference, not on energy content. Heat could flow from low energy to high energy, if the low energy object has a higher temperature."
     
  15. Sep 19, 2006 #14

    Andrew Mason

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    Well, the question is not all that clear. I interpreted "flow from the lower energy to higher" as "flow from the object whose molecules have lower energy to an object whose molecules have higher energy". Otherwise it is a meaningless question. One may as well ask whether heat can flow from a blue object to a green object. Total energy content (or colour) has nothing to do with heat flow.

    AM
     
  16. Sep 19, 2006 #15

    Doc Al

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    Exactly. All the more reason to make the answer clear, which you did.
     
  17. Sep 22, 2006 #16
    no it wouldn't
    the rule is unique: the energy flows from the hot object to the cold one
     
  18. Sep 22, 2006 #17

    SGT

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    The second part of your answer is true, but high temperature means more energy then low only if the two bodies have the same mass. Read the preceding answers.
     
    Last edited by a moderator: Sep 22, 2006
  19. Sep 23, 2006 #18

    Andrew Mason

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    They don't have to have the same mass.

    AM
     
  20. Sep 23, 2006 #19

    SGT

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    No, they don't, but if they do and if they have the same heat capacity, certainly the hotter body contains more energy than the cold one.
    Two liters of water at 0 degrees C have more energy than one liter at 100 C.
     
  21. Sep 23, 2006 #20

    Andrew Mason

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    I understand what you are saying. But the fact is that the heat flows by molecular collisions and the heat gradually disperses among all three litres. At all times, heat is flowing from matter at high energy to matter at low energy. It does not flow from the hot water to the cold water as a whole. It does it in little bits, and in each little bit the heat flows from high energy to low energy matter.

    AM
     
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