WEDGE

In Geometry, a solid having five sides or faces, three of which are rectangles, and the remaining two consequently triangles, and parallel to each other; hence the wedge, considered as a geometrical figure, is a prism with a triangular base. Its content is therefore equal to the area of the triangular base multiplied into the distance between the parallel planes. Wedge, in Mechanics, is one of the five simple engines or mechanical powers, and is used sometimes for raising bodies, but more frequently for dividing or splitting them. In the former case, if we suppose the wedge to be urged by pre ure, the action of the wedge is precisely the same as that of the inclined plane; for it is evidently the same, in point of mechanical advantage, whether the wedge be pushed under the load, or the load be drawn over the plane. The power is therefore to the force to be overcome as the tangent of the angle of the penetrating sides to the radius, leaving the friction out of consideration: hence the thinner the Wedge the greater is its effect. But when the wedge, as is generally the case, is driven forward by percu ion, its power cannot be estimated with any degree of accuracy. The percu ive tremor excited by the blow destroys for an instant the friction at the sides, and augments prodigiously the penetrating effect. Besides, when the wedge is used in rending wood or other substances, the parts of the block are generally separated to a considerable distance before the edge of the wedge, as in the annexed figure; in which case it acts besides as a lever, the power being applied at the end of the block or acting part of the wedge, and the resistance being at the point where the fibres begin to separate. All the various kinds of cutting and piercing tools, as axes, knives, sci ars, chisels, ., nails, pins, awls, ., are modifications of the wedge. The angle in these cases is more or le acute, according to the purpose to which it is applied. The mechanical advantage is increased by diminishing the angle of the wedge; but the strength of the tool is thereby also diminished. In tools for cutting wood the angle is generally about 30°; for iron it is from 50° to 60°; and for bra from 80° to 90°. In general, the softer the substance to be divided is, the more acute may the wedge be constructed. [s. 1334]