The power of the wedge increases in proportion as its angle is acute. In tools intended for cutting wood the angle is commonly about 30°; for iron from 50° to 60°; and for brass from 80° to 90°.
Case 1.—When two bodies are forced from one another, by means of a wedge, in a direction parallel to its back.
Rule.—As the length of the wedge is to half its back, or head, so is the resistance, to the power.
Example.—The breadth of the back, or head of the wedge, being three inches, and the length of either of its inclined sides 10 inches, required the power necessary to separate two substances, with a force of 150 lb.
As 10 : 1½ :: 150 : 22½ lb. Ans.
Case 2.—When only one of the bodies is moveable.
Rule.—As the length of the wedge, is to its back, or head, so is the resistance, to the power.
Example.—The breadth, length, and force, the same as in the last example.
As 10 : 3 :: 150 : 45 lb. Ans.
THE SCREW.