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Title: Moving force
Original Title: Force mouvante
Volume and Page: Vol. 7 (1757), p. 120
Author: Jean-Baptiste le Rond d'Alembert
Translator: John S.D. Glaus [The Euler Society, restinn@roadrunner.com]
Original Version (ARTFL): Link
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URL: http://hdl.handle.net/2027/spo.did2222.0000.760
Citation (MLA): d'Alembert, Jean-Baptiste le Rond. "Moving force." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by John S.D. Glaus. Ann Arbor: Michigan Publishing, University of Michigan Library, 2007. Web. [fill in today's date in the form 18 Apr. 2009 and remove square brackets]. <http://hdl.handle.net/2027/spo.did2222.0000.760>. Trans. of "Force mouvante," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 7. Paris, 1757.
Citation (Chicago): d'Alembert, Jean-Baptiste le Rond. "Moving force." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by John S.D. Glaus. Ann Arbor: Michigan Publishing, University of Michigan Library, 2007. http://hdl.handle.net/2027/spo.did2222.0000.760 (accessed [fill in today's date in the form April 18, 2009 and remove square brackets]). Originally published as "Force mouvante," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, 7:120 (Paris, 1757).

Moving force is the same things as motor force , however it is not a word that is used except to designate the forces which act advantageously through the use of machinery. Thus we have named amongst ourselves moving force that which others called mechanical strength. These are the simple machines which are mentioned in the elements of Statics and a combination of which all other machinery is made up; which includes the lever, the inclined plane, the screw, the wedge, the pulley. One can reduce these to two—the lever and the inclined plane—since the screw can be reduced to the inclined plane and the lever to the pulley and the wedge to the lever. See Screw, Wedge, Pulley, etc.

These different machines facilitate the action of the forces to move weights; either because they reduce in effect the action that the force would be obliged to exercise the weight immediately or because of the way in which the force is applied favors its action. Thus with the pulley, for example, the power must be equal to the weight, however the pulley helps the force , because the way in which the force is applied facilitates its action and conveniently places it in a state without obstacles. See Pulley, etc. To these five moving forces or simple machines, Mr. Varignon adds a sixth into his project de Mécanique which he calls the funicular (cog train) which is nothing more than an assembly of ropes by which the weight is pulled by different forces . See Funicular. To understand the effect of these different machines it is necessary to calculate it within the framework of equilibrium, since when one has the strength capable to sustain a weight, then by increasing this strength the weight will move. However by calculating in the case of equilibrium it is sufficient to employ the principle of the composition and decomposition of forces . To do so, it is first of all necessary to prolong the direction of the two random forces and to seek out the former and then the latter and a third force and so on, until one has arrived at the last force which has to be equal to 0 or at least to have passed by a fixed point for it to have equilibrium. In effect, if this last force , which is the result of all the others, was not equal to zero and did not pass through a fixed point for which the resistance eliminates its action, then there would be no equilibrium, as it is suggested, since this force would then produce some motion. This principle concerning the reduction to only one force contains all of Statics and one can see the articles to which this applies to different machines.