"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 split ing them. In the former case, if we suppose the wedge to be urged by pres sure, the action of the wedge is pre cisely 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, leav ing 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 percussion, its power cannot be esti mated with any degree of accuracy. The percussive 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 ; 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, scissors, chisels, &c., nails, pins, awls, &c., are modifications of the wedge. The angle in these cases is more or less acute, ac cording to the purpose to which it is applied. The mechanical advantage is increased by diminishing the angle of the wedge ; hut the strength of the tool is thereby also diminished. In tools for cutting wood the angle is generally about for iron it is from to and for brass from to 900. In general, the softer the substance to be divided is, the more acute may the wedge be constructed.