. Practical physics. Exs = , that is, aUhough the effort E is only - of the resistance li, the woi-k put into the machine hy the effort E isequal to the work accomplished hy themachine against the resistance R. 129. Mechanical advantage. Theabove experiments show that it is sometimes possible by applying a small force E to overcomea much larger resisting force it. The ratio of the resistance Bto the effort E (ignoring frictioTi) is called the mechanical advan-tage of the machine. Thus, the mechanical advantage of thesingle fixed pulley is 1, that of the single movable pulley is2, that of t
. Practical physics. Exs = , that is, aUhough the effort E is only - of the resistance li, the woi-k put into the machine hy the effort E isequal to the work accomplished hy themachine against the resistance R. 129. Mechanical advantage. Theabove experiments show that it is sometimes possible by applying a small force E to overcomea much larger resisting force it. The ratio of the resistance Bto the effort E (ignoring frictioTi) is called the mechanical advan-tage of the machine. Thus, the mechanical advantage of thesingle fixed pulley is 1, that of the single movable pulley is2, that of the system of pulleys shown in Fig. 116 is 6, etc. If the acting force is applied at B instead of at E the me-chanical advantage of the systems of pulleys of Fig. 116 is i;for it requires an application of 6 pounds at B to lift 1 poundat E. But it will be observed that the resisting force at E nowmoves six times as fast and six times as far as the acting forceat B. We can thus either sacrifice speed to gain force, or. Fig. 116. Combinationsof pulleys 110 WOEK AND MECHANICAL ENERGY sacrifice force to gain speed; but in every case, whatever wegain in the one we lose in the other. Thus in the hydrauhcelevator shown in Fig. 13, p. 18, the cage moves only as fastas the piston ; but in that shown in Fig. 14 it moves four timesas fast. Hence the force applied to the piston in the lattercase must be four times as great as m the former if the sameload is to be lifted. This means thsrt the diameter of the lattercylinder must be twice as great. QUESTIONS AND PROBLEMS 1. Although the mechanical advantage of the fixed pulley is only 1,it is extensively used in connection with clothes lines, awnings, openwells, and flags. Explain. 2. If the hydraulic elevator of Fig. 14, p. 18, is to carry a total loadof 20,000 lb., what force must be applied to the piston? If the waterpressure is 70 lb. per square inch, what must be the area of the piston ? 3. Draw a diagram of a set of pulleys by which a fo
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectphysics, bookyear1922
