Question on Perpetual Motion of Second Kind

I made up two designs for perpetual motion machines of the second kind.
That is, one that converts heat from a single isothermal source directly
into useful work, thus lowering the entropy of the universe in violation of
the second law of thermodynamics. I'd REALLY like to know why they don't
work. I've done a little reading into Maxwell's Demon and information
theory lately, but I still can't figure out the answer to these specific
designs.

Here they are: [Only registered users see links. ]

I'd really like to do my physics undergraduate thesis on the topic of
perpetual motion of the second kind this semester, so any answers you may
have would help me a lot. Thanks!

-Ben

"Ben Peterson" <[Only registered users see links. ]> wrote in message news:<bv7pjn$lt2$[Only registered users see links. ].umn.edu>...


Machine #1:

The pressure of the gas is constant, so the piston should not move
over macroscopic distances, apart the small fluctuations.
But piston and generator are outside the isothermal bath, so you have
to show us that they are not at a different temperature.
Also, you should provvide an example of useful work in the drawing
(like lifting a weight).

There are examples of extracting work from brownian motion that use
asymmetric systems (like a piston that move only in one direction).

Machine #2:

The mirror has a temperature and emits and absorbs thermal radiation.
So do the two points. I would expect that the thermal radiation from
the mirror affects the blue and red point.
If no work is done to keep the temperatures of the mirror and the
points constant, then the system will end up at equilibrium.
(A mirror that reflects all EM frequencies does not exist.)


OC

Ben Peterson wrote:

I invented something similar:

[Only registered users see links. ]

If you find some comprehensive explanations why it doesn't work
I'm interested.

Bernhard

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In article <bv7pjn$lt2$[Only registered users see links. ].umn.edu>,
Ben Peterson <[Only registered users see links. ]> wrote:

In machine #1, you don't even need the piston and generator because there
will be thermal noise anyway. Put an oscilliscope across a resistor and
you can see it. Sensors are often cooled to reduce thermal noise. But
what that also means in your machine is sometimes the generator will act
like a motor and move the piston against incoming molecules. Expect them
to gain as much energy as they lose, and the temperature to remain
constant.

Turning thermal noise into useful work is another matter; diodes have
thermal noise, too. The second law can be violated in microscopic scales,
but a perpetual motion machine that does something is a macroscopic
device.

Machine #2 is quite clever. Thermal radiation from the mirror will go in
every direction, and any blackbody will absorb as well as it emits. But I
can't think of a good reason to kill a transient dT/dt>0.

--
"In any case, don't stress too much--cortisol inhibits muscular
hypertrophy. " -- Eric Dodd

"Ben Peterson" <[Only registered users see links. ]> wrote in message
news:bv7pjn$lt2$[Only registered users see links. ].umn.edu...
of

Because your "invention" will vioolate the second law of thermodynamics.

Franz

Ben Peterson wrote:
[snip]

You are wrong - unless you can flip an honest coin heads 10^23 times
in a row. A machine does work. it cannot evade the Second Law.

--
Uncle Al
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(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!

"Bernhard Kuemel" <[Only registered users see links. ]> wrote in message
news:4017ad94$[Only registered users see links. ]...
may

Others have mentioned that the machines all violate the second law of
thermodynamics. To put it another way, none of the processes that are to be
used can operate at 100% efficiency.

"Franz Heymann" <[Only registered users see links. ]> wrote:

I break the law daily. Not the second law (twice a day I drive faster
than the posted speed limit on this bridge:
[Only registered users see links. ] - the site is kind of humerous) but
what's the difference?

Does anyone know where I can get me a demon like the one Maxwell had?

Thanks!

Ben Peterson wrote:

Second Law of Thermodynamics
[Only registered users see links. ]

The second law of thermodynamics prohibits the construction of a perpetual
motion machine "of the second kind."

tadchem wrote:

Encyclopedia of Irish Erotic Pottery
Compendium of French Military Triumphs
The Big Book of British Gourmet Cooking
Biographies of Black African Mathematicians
Directory of Mexican Birth Control Clinics

--
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[Only registered users see links. ]
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!