Entropy...the basic idea?

Discussion in 'Physics & Math' started by Quantum Quack, Jan 3, 2004.

  1. Quantum Quack Life's a tease... Valued Senior Member

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    I wanted to pass this by you guys just to see if I got this basically right.

    say we have 4 hot objects 100deg and 4 cool objects 50deg in a closed system. The medium is say air.

    Entropy would suggest that in time the 8 objects would transfer energy unitl a state of temperature of energy equalibrium was achieved thus all in the system would reach an equal energistic state of say 75 degrees, all 8 objects and the medium air would equalise at 75 degres or some temperature that would be equal through out.


    If this is the case then thinking locallyand in absolute terms, the sun should be slowly cooling and the earth should be slowly heating.

    Knowing that the universe is slowly evening out it's energy means that eventually the universe will cease to move thus becoming zero.

    Have I got this right?

    Is this the unhindered aspect of Entropy, as defined in the 2nd law of thermodynamics in basic form?
     
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  3. NanoTec Registered Senior Member

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    It is not entirely an “evening out” of energy, all objects with entropy radiate, and thus all mater in the universe will eventually radiate to form non interacting photons. It will be very cold but still not have zero temperature. Until an infinite amount of time has passed.

    The second law states: Processes in which the entropy of an isolated system would decrease do not occur.
    Clausius sates that it is: No process is possible whose sole result is a heat flow out of one system at a given temperature and a heat flow of the same magnitude into a second system at a higher temperature.
    Kelvin-Plank statement: No process is possible whose sole result is a heat flow out of a reservoir at a single temperature, and the performance of work equal in magnitude.

    Two systems of differing temperatures brought into contact will come to an equilibrium temperature. One system will transfer an energy Q to another. It will decrease in temperature based on its specific heat dQ=C*dT, and the other will increase. The change in entropy for each individual system is dS=dQ/T0
     
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  5. Quantum Quack Life's a tease... Valued Senior Member

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    just a thought,
    Does the fact that the earths roatation has stopped slowing down and has maintained it's rotational speed or energy for the last five years mean that the planets entropy has shifted some how?
     
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  7. John Connellan Valued Senior Member

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    Not necessarily! The sun may be increasing in temperature but its overall entropy can still be increasing too.

    There is no way the earths rotation has stopped slowing down!
     
  8. Quantum Quack Life's a tease... Valued Senior Member

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  9. HallsofIvy Registered Senior Member

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    An important difference between your first example and the example of the sun and earth is that all of your "objects" contain heat which they are losing (or gaining) by radiation and convection. The sun is still producing heat by fusion and so is not cooling.

    "Knowing that the universe is slowly evening out it's energy means that eventually the universe will cease to move thus becoming zero.

    Have I got this right?"

    I wouldn't say "cease to move". I would say moving at random (motion is, after all, relative) so that no part has more energy than any other. This is known as the "heat death" of the universe.
     

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