Rob Twiss wrote:
>...
>> Koenemann's 'theory' apparently leads to the dimensionally
>> impossible conclusion that force per unit area scales differently from
>> energy per unit volume. It must therefore contain an error.
At 09:34 PM 2001/07/09 +0200, Falk Koenemann responded:
>Prove me wrong.
At 09:33 PM 2001/07/09 +0200, Falk Koenemann evidently proved himself wrong
on this point, by insisting that P is not equal to f/A in a spherical
system that is changing scale at constant state, thus contravening Newton's
definition P = f/A:
>>...One can only feel wistful at the thought of living in a world in which
>>pressure (f/A) could be increased just by subdividing a system into a
>>number of smaller systems, thus storing potential energy without having
>>to do any work!
>
>No, Dugald, you have demonstrated my point! f/A is not a useful term because
>it is scale-dependent. But if you consider P only and exclusively the energy
>density you will find that the ratio U/V is scale-independent.
It is not practical to "consider P only and exclusively the energy
density", because energy density is not directly measureable. To determine
changes in the energy density of any real substance it is necessary to
measure/monitor/control its P, V and T. P can be
measured/monitored/controlled only by means of devices that rely on
Newton's definition P = f/A, which is universally valid for macroscopic
systems. For example, "the pressure exerted on a manometer is the mean
change in the momentum of the molecules per unit time and surface area."
(Denbigh 1966 The Principles of Chemical Equilibrium 2nd ed, p335).
Dugald M Carmichael Phone/V-mail: 613-533-6182
Dept of Geological Sciences and Geological Engineering
Queen's University FAX: 613-533-6592
Kingston ON K7L3N6 E-mail: [log in to unmask]
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