Cyclopedia of architecture, carpentry, and building : a general reference work . t of a force for conven-ience; the rule used herein is as follows: The Dioinent of aforce about a point is positive or negative according as it tendsto turn the hody cdjout that point in the clochwise or counter-clochwise direction-^. Thus the moment (Fig. 7) of Fj about O is negative, about O positive;u p a O a u about O negative. 30, Principle of Moments. In general, a single force ofproper magnitude and line of ac-tion can balance any number offorces. That sinMe force is calledthe equililjrant of the forces, an
Cyclopedia of architecture, carpentry, and building : a general reference work . t of a force for conven-ience; the rule used herein is as follows: The Dioinent of aforce about a point is positive or negative according as it tendsto turn the hody cdjout that point in the clochwise or counter-clochwise direction-^. Thus the moment (Fig. 7) of Fj about O is negative, about O positive;u p a O a u about O negative. 30, Principle of Moments. In general, a single force ofproper magnitude and line of ac-tion can balance any number offorces. That sinMe force is calledthe equililjrant of the forces, andthe single force that would balancethe equilibrant is called the result-ant of the forces. Or, otherwisestated, the resultant of any num-ber of forces is a force which pro- ^1duces the same effect. It can beproved that—The cdgehraic sumof the moments of any numderof forces with respect to a pointyequcds the moment of their re-sultant ahout thatp)dnt. *By clockwise direction is meant that in which the hands of a clockrotate; and by counter-clockwise, the opposite Fi-. 7. 27 20 STRENGTH OF MATERIALS This is a useful principle and is called principle of moments. 31, All the forces acting upon a body which is at rest are said to be halanced or in eqtdlihrium. No force is required to balance such forces and hence their equilibrant and resultant are zero. Since their resultant is zero, the algebraic sum of the inoin- aooolbs. 2000II0S. loooltos. p la 3000lbS. ?^2-^ f b3obolbs. Fig. 8. ents of any niiinher of forces which ar^e halanced or in equilib-rium equals zero. This is known as the principle of moments for forces inequilibrium; for brevity we shall call it also the principle ofmoments. The principle is easily verified in a simple case. Thus, letAB (Fig. 8) be a beam resting on supports at C and F. It isevident from the symmetry of the loading that each reactionequals one-half of the whole load, that is, \ of 6,000=3,000pounds. (We neglect the weight
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