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Second law of thermodynamics,

  1. Sep 11, 2009 #1
    The second law of thermodyanics states that heat cannot flow from a colder region of space to a hotter region; When you open a door that previously separates your warm house from the cold outside; What substance/process is flowing then to drive the heat out of your warm house to make your house cold ?
  2. jcsd
  3. Sep 11, 2009 #2
    The temperature difference between the inside and outside temperatures is what drives the process.

  4. Sep 11, 2009 #3
    but the second law does not state that heat cannot flow from a cold to hot body,it can flow but some work must be expended to achieve it.
  5. Sep 11, 2009 #4
    Yes, that is why air conditioning is costly.
  6. Sep 11, 2009 #5
  7. Sep 11, 2009 #6
    Also, the heat from your house flows to the colder region making the house itself colder and the colder region hotter.
  8. Sep 12, 2009 #7
    When you open a door and the house cools that is not the second law of thermodynamics at work it is simply warm air from the house flowing out and being replaced by cool air from the outside. What the second law says is if you have a hot brick in a cold room the brick will always cool down and never warm up.
  9. Sep 14, 2009 #8


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    come on folks - cold air is denser than warm air, and that drives convection. Also conduction exists but it is minor
    anyhow do not be fooled, heat flows from cold to hot and from hot to cold. What? Yup. It is just that the net flow of heat is generally from hot to cold
  10. Sep 16, 2009 #9


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    God I know what my gut tells me about the second law, it is just that I am not fully armed to take it down yet. No matter I will answer you in part.

    To me the second law is a result of our thermodynamic perspective. I started a new thread so go read it if you care to and if so thanks. And yes it was backed by statistical arguments but they are primarily based upon our isothermal isobaric world (I know I may be biting off a bit too much cuz it has been too long since I studied the statistical stuff.

    To me in part, the problem may have some origins in our omitting blackbody radiation from a system’s energy. I am sorry but that is all I can say until I get my head around something.

    I will say this I believe that people like the guy who did the marble experiment a few years back and Dan Sheehan are right, that the second law needs to be challenged

    Sheehan 52stated that: “The second law of thermodynamics is an empirical law. It has no fully satisfactory theoretical proof. This being the case, its absolute validity depends upon its continued experimental verification in all thermodynamic regimes.”

    To me the second law is a result, as witnessed by us residing upon isobaric isothermal mother Earth. The key word, being result. I frown when we use it as a reason , i.e. cosmology.

    Can I leave it at that for now, while I ponder how to rattle its cage in the simplest terms because complicated arguments cannot be defended by anyone. The corollary remains that complicated arguments also cannot be defeated by anyone

    Cheers and I need a beer
    Talk to you tomorrow
  11. Sep 16, 2009 #10


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    Homework Helper

    Um, who's Sheehan? And...Earth is neither isobaric nor isothermal.
  12. Sep 17, 2009 #11
    why on earth should the second law of thermodynamics be an empirical ?
    it does have a valid proof
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