. A text book of elementary mechanics, for the use of colleges and schools. Fig. 71. 140.] KESOLUTKXN OF FORCES. 147 during no effect, and the other perpendicular, ad. But the vesselis headed in the direction BR; hence to rind the effective compo-nent of the wind in this direction the force ad must be again re-solved into the components af and ae. The tendency of af is todrift the vessel to leeward, and is nearly balanced by the resist-ance of the side of the vessel and keel (and the centre-board in. Fig. 72. Fig. 73. the case of a sail-boat) against the water, and the component for-ward is ae
. A text book of elementary mechanics, for the use of colleges and schools. Fig. 71. 140.] KESOLUTKXN OF FORCES. 147 during no effect, and the other perpendicular, ad. But the vesselis headed in the direction BR; hence to rind the effective compo-nent of the wind in this direction the force ad must be again re-solved into the components af and ae. The tendency of af is todrift the vessel to leeward, and is nearly balanced by the resist-ance of the side of the vessel and keel (and the centre-board in. Fig. 72. Fig. 73. the case of a sail-boat) against the water, and the component for-ward is ae. As a matter of fact there is always a little drifting,whence the motion of the boat is kept in the required directionby the rudder. The action of the rudder is itself another exam-ple of the same principle. It is seen in the figures that w^ith thesame wind two vessels may sail in exactly opposite directions. An explanation similar to the above may be applied to themotion of a windmill. 140. Resolution of Forces along Two Axes at RightAngles to each other. The principle of the resolution ofa force along two axes at right angles to each other maybe conveniently employed to obtain the resultant of anumber of forces acting at a common point. Let theforces P, Q, S, T (Fig. 74) be represented by AB, AC,AD, AE, and let X and Y be any two axes at right an- 148 STATICS, [140, gles to each other passing through A. The componentsof P, Q, S, T are, geometrically, on the axis X. ... Ab, —Ac, — Ad, A
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