. A text book of elementary mechanics, for the use of colleges and schools. In the Steelyard we have,in the place of the fixed arm and varying counterpoiseof the ordinary balance, a varying lever-arm and a fixedcounterpoise. The bar is made heavier at one extremity,and to this end is attached the hook or scale-pan; nearit is the point of support. This axis is consequentlynear the centre of gravity of the whole, but usually doesnot coincide with it. In order to graduate the steelyard,it is necessary to determine first the zero-point of thescale, and then the distance to be marked off from it fo
. A text book of elementary mechanics, for the use of colleges and schools. In the Steelyard we have,in the place of the fixed arm and varying counterpoiseof the ordinary balance, a varying lever-arm and a fixedcounterpoise. The bar is made heavier at one extremity,and to this end is attached the hook or scale-pan; nearit is the point of support. This axis is consequentlynear the centre of gravity of the whole, but usually doesnot coincide with it. In order to graduate the steelyard,it is necessary to determine first the zero-point of thescale, and then the distance to be marked off from it foreach unit of weight (, 1 lb.) and fraction of it. Let AB (Fig. 138) be the steelyard, supported at the weight of the whole by Q acting at thecentre of gravity G. In order that the bar shouldbalance horizontally about C when there is no weight 206 STATICS. [194. on the hook, it is necessary to place the selected counter-poise P at such a point, D, that Q. CG = P. CD. This point D is then the zero of the scale, or the posi-tion of P for 0 lbs. at J. J? C 6. Fig. 138. Fig. 139. Let now a weight W be placed on the hook so thatit acts through A) then the counterpoise P will balanceit at B, if (156) the moments about 0 vanish; that is, + = ; or, since = , = - = P (CB - CD), or , and DB = If W = 1 lb., then the value of Z>P gives the positionof the one-pound notch on the scale, and at twice thisdistance from D will be the two-pound notch, and so , as in Fig. 139, the centre of gravity is on the otherside of the fulcrum, the position of the zero-point Dwill also be changed, but the value of DB is obtained inessentially the same way. 195.] STEELYAKD. 207 195. A form of the steelyard as actually employed isseen in Fig. 140. It will be observed that both sides ofthe bar are graduated, and moreover there is a second
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectmechanics, bookyear18
