Talk:Thomas Newcomen/Material from Wikipedia user Dr. Gabriel Gojon/Vis Viva Versus Mechanics
Vis Viva Versus Mechanics Consider the implications of the Papin-Leibniz discussion once the word effect is translated to the modern term WORK. Both Leibniz and Papin agreed that the useful work performed by a heat engine, was to be measured by the height to which it could raise a given quantity of water. In his dynamics, Leibniz had used the example of the equivalence of the work required to raise a heavy body a given height, to the vis viva acquired by the body in falling from that height. Whereas in the case of the falling body, the vis viva is measured by the body's velocity, Leibniz proposed to measure the vis viva of expanding steam by its temperature. Applying the principle of the conservation of vis viva, Leibniz developed the following sort of relation:
vis viva consumed by machine = useful work (height a given quantity of water is raised) + heat lost in overcoming friction + heat lost to superfluous cooling + . . . [other inefficiencies]
With this sort of analysis, Leibniz was prepared to compare the thermodynamic efficiencies of heat engines by measuring "the degree of heat required to make a given effect." This also led him to the formulation of his unique experiment: demonstrating that steam can "raise more than a column of air", i.e., that the direct power of expanding steam is greater than mere atmospheric pressure.
Consider the case of Papin's 1690 steam engine. Here the atmospheric pressure alone, considered as a "column of air" resting on the cylinder, is responsible for the motion of the piston. The role of the expanding steam is simply to raise the piston back to the top of the cylinder; that is, in Leibniz's phrase, "to raise a column of air." Then, the condensed steam leaves a vacuum in the cylinder, and atmospheric pressure pushes the piston downward once again.
Leibniz proposed to demonstrate that the direct force of expanding steam, unlike mere suction, is unbounded that it can "raise more than a column of air" (Aug. 28, 1698):
"There is nothing which merits development more than the force of expansion [la dilation]; if one objects that expanded water can do no more than raise a cylinder of air, and that the stronger it [steam] is the higher it [cylinder of air] is raised, and that therefore it is sufficient to use the weight of the falling cylinder -I reply that this higher elevation requires more time, allowing the steam to gradually cool, than a quicker elevation of a heavier weight. Thus, either force is lost, or more fire must be used [emphasis added]." Clearly at issue in this "little test" is the validity of the mechanical world view, that threatened to impose itself on emerging technology. Was steam power to be constrained to act passively, slowly pushing and pulling weights like some grotesque Rube Goldberg type of lever or pulley, or was it to be freed in all its "violence"- maximum vis viva-- to effect a qualitative human advance? From this dynamical point of view, in fact, Leibniz was by no means convinced that expanding steam was the optimum source of power for the new technology. For him, even expanding steam was not sufficiently violent or rapid in its action, compared, for example, to exploding gunpowder or, as he suggests elsewhere, to the combustion of alcohol. He argued as well for further work in applying the force of highly compressed air, pointing out its advantages for building lighter and more portable engines for vehicles.