. A text book of elementary mechanics, for the use of colleges and schools. htis to the perpendicular distance from the fulcrum to thedirection of the Poiver. For example, in Figs. 126, 127, 128, where the bar is A F B \A_ B F If I 2T Fig. 126. Fig. 127. Fig. 128. straight and the power and weight act at right anglesto it, , P_ BF_or W ~ AF The rule holds good equally well when the bar is notstraight and the directions are oblique. The positions 186.] LEVER. 197 of the perpendicular distances from the fulcrum—thatis, the arms of P and W—are to be carefully noted inthe following figur
. A text book of elementary mechanics, for the use of colleges and schools. htis to the perpendicular distance from the fulcrum to thedirection of the Poiver. For example, in Figs. 126, 127, 128, where the bar is A F B \A_ B F If I 2T Fig. 126. Fig. 127. Fig. 128. straight and the power and weight act at right anglesto it, , P_ BF_or W ~ AF The rule holds good equally well when the bar is notstraight and the directions are oblique. The positions 186.] LEVER. 197 of the perpendicular distances from the fulcrum—thatis, the arms of P and W—are to be carefully noted inthe following figures, 129-134. For all of them thesame equation holds good. The pressure on the fulcrum (the weight of the leverbeing neglected) in Figs. 126 and 129 is P + W, in it is W- P, in Fig. 128 it is P - W, and in theother figures it may be calculated by the parallelogramof forces. In the latter cases it is to be noted that,since the power, weight, and resistance of the fulcrumare in equilibrium, their lines of action produced mustpass through the same point (158, B).. Fig. 129. Fig. 131. In Fig. 132 the lever is curved like an iron pump-handle, the arms of the weight and power are the per- .*,.*•. A e^k^...* v7f Fig. 132. pendiculars BF and AF respectively, and the aboveequation is true: 198 STATICS. (187. 187. Three Kinds of Lever. The three forms in , 127, 128 are sometimes called the three kinds oflever, though there is no essential difference betweenthem. In the first kind the fulcrum is between thepower and weight; if nearer to the latter, there is a . mechanical advantage; if nearer to the power, a mechan-ical disadvantage. If the arms are equal, then P = W,as in the ordinary balance (191). In the second kind the fulcrum is at the end, and theweight nearer to it than is the power; in this case thereis always a mechanical advantage. In the third kind the fulcrum is at the end, but thepower is nearer to it than the weight, and there is there-fore a
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