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752Re: Dippy bird

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  • Sam
    May 30, 2003
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      COMMENT BELOW:

      --- In AMBIENTENERGY@yahoogroups.com, "Phil Karn" <anonanon7@y...>
      wrote:
      > --- In AMBIENTENERGY@y..., "marvinjasoncarter"
      > <marvinjasoncarter@y...> wrote:
      > > Mr. Phil,
      > >
      > > I've been thinking about your statement which says "when the
      water
      > > runs out, the bird stops even though there is plenty of heat left
      > in
      > > the atmosphere." I have heard this said before and don't
      > understand
      > > what it proves.
      >
      > It proves a great deal.
      >
      > First, let's look at the laws of thermodynamics. The first law says
      > that energy is conserved. (Actually, it's the sum of mass plus
      energy,
      > but that Einsteinean detail is not important here.)
      >
      > The second law says that in any spontaneous process, the entropy of
      > a closed system must always increase.
      >
      > "Entropy" has units of heat energy divided by absolute
      temperature, so
      > when heat flows from a hot source into a cold sink it increases the
      > sink's entropy by more than it decreases the source's entropy.
      > Therefore the second law permits heat to flow spontaneously from a
      hot
      > object to a cold object until the two objects are at the same
      > temperature. Then the heat flow must stop.
      >
      > Any real system, such as an engine, must obey both laws of
      > thermodynamics at all times.
      >
      > The second law explains why it is not possible to build an engine
      > whose sole function is to convert heat from a single reservoir
      (e.g.,
      > the atmosphere) into useful work.
      >
      > The toy bird does indeed convert heat from the atmosphere into (a
      > small amount) of useful work, BUT THAT IS NOT ITS ONLY RESULT -- it
      > also evaporates water. And it just so happens that when you
      evaporate
      > water, you increase its entropy. A lot. So much so that its entropy
      > can increase even when its temperature decreases; that's how "swamp
      > coolers" can work.
      >
      > The dippy bird increases the entropy of the water it evaporates by
      > more than it decreases the entropy of the atmosphere by removing
      heat
      > from it. This satisfies the second law, so it can run
      spontaneously.
      >
      > But without liquid water to evaporate, the bird no longer has
      > something whose entropy can be increased. So it stops running. To
      > continue running it would have to decrease the total entropy of the
      > universe, and that's directly forbidden by the second law.
      >
      > Phil

      Phil,

      If I put a dippy bird in glass container and put him in water up
      to his ankles and sealed the glass container would he ever run out
      of water? IF so, where does the water go?

      Inquiring minds just gotta know...
      SD
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