Art wrote:Hi Ecci ,
"His definition is correct. a PMM is one that would not require an external driving force to sustain its motion. "
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Well his definition is daft .
To sustain its motion - in relation to what ?
If we magically remove all of the Universe from the PMM then what is it in motion in relation to ?
What is the motion of anything in relation to? You can pick any point for reference. For our purposes the practical reference point is earth. A PMM wouldn't need an external energy to sustain its motion relative to earth. Removing the universe would leave you the observer as the reference point.
His Quote :-""It follows thence that the total quantity of all the forces capable of work in the whole universe
remains eternal and unchanged throughout all their changes . "
The inside of any machine and the outside of any machine are intrinsically connected to the Universe of forces by his own admission . So why should it matter if the cause of the motion (perpetual or not ) is manifested from inside the machine or outside ?
It matters because when we measure a system (machine) before and after any work has been done, the measurement shows the total energy (inside
and outside) didn't change. Your question is answered in his summary that all internal energy is traceable to a an outside source (vegetable life, the sun). If we allowed our definition of PM to manifest energy from external sources, then by definition,
everything would be a PM (until the external source is exhausted, or parts wear out). That sounds familiar doesn't it?
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"All input energy in a system is eventually lost to heat as Helmholtz says. "
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Merely the result of the forces "remaining eternal and unchanged" .
One motion of wheel (perpetually hopefully) being changed to another motion of molecules (perpetual definitely) .
So not lost . "eternal and unchanged throughout all their changes . "
Thermodynamics is heat (motion) bookkeeping .
It cannot and does not negate 'perpetual' motion in any way.
When I say "lost" to heat, I don't mean off the books. I think you know what I mean (hopefully).
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"His reasoning is not circular as some believe. "
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Well , how about -
A few paragraphs above the one quoted :-
"It follows thence that the total quantity of all the forces capable of work in the whole universe remains eternal and unchanged throughout all their changes . "
Thats a defining statement , = Steady state Universe , nothing is created , nothing is destroyed .
And then he says in the paragraph quoted , - "...the law of conservation of force...might also be expressed in the practical form that no perpetual motion is possible , that force cannot be produced from nothing ;.. "
I think thats a bit of circular thinking ! , (1) Define "force cannot be produced from nothing " Then (2) "...the law of conservation of force ...might be expressed in the practical form that no perpetual motion is possible , that force cannot be produced from nothing " and then (3 ) declare PMM is impossible because force cannot be produced from nothing and ignore the fact that whether or not force is produced from nothing has absolutely nothing to do with how it 'perpetuates' or transfers from place to place.
In the paragraph before the one you quoted he says:
Helmholtz wrote:
I have stated how we are accustomed to measure mechanical work, and how the equivalent in work of heat may be found. The equivalent in work of chemical processes is again measured by the heat which they produce. By similar relations, the equivalent in work of the other natural forces may be expressed in terms of mechanical work.
If, now, a certain quantity of mechanical work is lost, there is obtained, as experiments made with the object of determining this point show, an equivalent quantity of heat, or, instead of this, of chemical force; and, conversely, when heat is lost, we gain an equivalent quantity of chemical or mechanical force; and, again, when chemical force disappears, an equivalent of heat or work; so that in all these interchanges between various inorganic natural forces working force may indeed disappear in one form, but then it reappears in exactly equivalent quantity in some other form; it is thus neither increased nor diminished, but always remains in exactly the same quantity. We shall subsequently see that the same law holds good also for processes in organic nature, so far as the facts have been tested.
How is this circular? Where does he say "Since no one has ever built a PMM, it must be impossible" ? He's trying to show WHY no one has managed to build one, using the evidence we have. If energy could be produced from nothing, it would show in some evidence.
Also
So whats his stated evidence for the "practical form that no perpetual motion is possible" ?
Further up in the paragraph :- " A machine which could produce work from nothing " (his definition of PMM)..."could not be produced by the aid of the then known mechanical forces (and which) could be demonstrated in the last century by the aid of the mathematical mechanics which had at that time been developed ."
He is using the same argument that Wagner used for the 'proof' that Bessler's wheel shouldn't work but without acknowledging (could he have been unaware of ?) the existance of Bessler's demonstration of a machine which seemed to satisfy the definition of a number of "mathematical mechanics" (of high regard at the time ) of what was widely interpreted and claimed as "perpetual" motion .
I don't know if Helmholtz was aware of Bessler.
I think what this quote is saying is that the math formulas up to the 18th century also showed PMMs were not possible; he's not referring to mathematicians.
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Defining PMM as a 'Perpetual Motion Machine' which must exhibit the achievement of a characteristic which by definition is stated as impossible is hardly reasonable .
Its more circular than our reasoning I think :)
That's not what the laws say. You're misstating them.
