Science for beginners . Fig. 286.—Beam balance. unequal arms is the old-fashioned steelyards (Fig. 287). Ifin such a balance, the object whose weight is to be determinedis 2 in. from the point of support while the known mass is 20in. from the support, then the weight of the unknown objectis exactly 10 times that of the known mass. The weight of the known mass : the weight of the unknownmass :: 2 : 20. The weights are inversely proportioned to the lengths ofthe arms. Generally, scales used in weighing heavy objects are con-structed by using several such beams in combination. Thecommon wagon sca
Science for beginners . Fig. 286.—Beam balance. unequal arms is the old-fashioned steelyards (Fig. 287). Ifin such a balance, the object whose weight is to be determinedis 2 in. from the point of support while the known mass is 20in. from the support, then the weight of the unknown objectis exactly 10 times that of the known mass. The weight of the known mass : the weight of the unknownmass :: 2 : 20. The weights are inversely proportioned to the lengths ofthe arms. Generally, scales used in weighing heavy objects are con-structed by using several such beams in combination. Thecommon wagon scales are a familiar example of such a com-bination of unequal armed beam balances (Fig. 288). In 472 MACHINES, WORK, AND ENERGY such cases, it is common for the beams to be so combined thata 1-lb. mass will balance, perhaps, 1000 lb. or Fig. 287.—Common steelyards. Fig. 288.—Wagon scales. 551. Spring Balances.—The principle of the spring bal-ance is very different. A coiled steel spring ismounted within a metal case (Fig. 289). Theupper end of this coiled spring is secured to theupper end of the case; the lower end of thespring is free but carries a small rod or wirewhich, in turn, carries the hook upon which themass whose weight is to be determined is hung. feE - i A small pointer, or index, fastened to the lower - end of the spring is so mounted that it hangs just in front of the face of the case, upon whichis stamped the scale. When a mass is suspendedon the hook, the coiled spring is stretched andthe index indicates the weight. Spring balances are very convenient and easyto handle but usually they are not very accur-ate. Even though a spring balance may be care-fully made and fairly accurate when new, it islikely to wear with use and give false readings
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectscience, bookyear1921
