# Elementary Introduction to Practical Mechanics, Illustrated by Numerous Examples; Being the 3D Ed. of "Elementary Examples in Practical Mechanics."

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1868 edition. Excerpt: ...resultant will be made to act at a continually increasing distance from q. Consequently, in the case supposed in the question, the resultant acts along a line as remote from q as is consistent with equilibrium. 87. Wheel and Axle, Pulleys.--The wheel and axle and the pulley are familiar examples of bodies capable of moving round a fixed axle; they may be sufficiently described as follows: --(1) The Wheel and Axle.--Let Ab represent a cylinder of wood or some other material called the axle, to the end of which is firmly fixed a cyUnder of a large diameter Ec called the wheel; they rest on a pair of bearings by means of a small cylindrical axis, one end of which is D, the geometrical axes of all these cylinders being coincident; ropes are wrapped in opposite directions round the wheel and axle respectively, to the ends of which weights p and Q are attached; if p is so large as to descend, it will do so by turning the machine; this will wind up Q's rope, and thereby cause that weight to ascend. It is usual to describe the wheel and axle in the above form, in order to give definiteness to the calculation; in practice, however, a winch commonly supplies the place of the wheel. (2) The Pulley is simply a thin cylinder with a groove cut in its circumference, on which a rope.-, can rest: the cylinder is capable of turning round an axis, which is supported by a piece called a block; this well known machine is represented in the accompanying diagram. When several pulleys are combined into a single machine, they constitute what is called a system of pulleys; the system most commonly used is called the block and tackle; it consists of two blocks containing pulleys (under W these circumstances called sheaves) which are either equal in number, or else the upper...