Fifth book of lessons for the use of schools . he wedge. But aknife cuts best when drawn across the substance it is todivide, as it is used in cutting meat; for the edge of aknife is really a very fine saw, and therefore acts bestwhen used like that instrument. THE SCREW. The screw, which is the last mechanical power, ismore complicated than the others. It is composed oftwo parts, the screw and the nut. The screw s is acylinder, with a spiral protuberance coiled round it,called the thread; the nut N isperforated to contain the screw;and the inside of the nut has aspiral groove, made to fit the
Fifth book of lessons for the use of schools . he wedge. But aknife cuts best when drawn across the substance it is todivide, as it is used in cutting meat; for the edge of aknife is really a very fine saw, and therefore acts bestwhen used like that instrument. THE SCREW. The screw, which is the last mechanical power, ismore complicated than the others. It is composed oftwo parts, the screw and the nut. The screw s is acylinder, with a spiral protuberance coiled round it,called the thread; the nut N isperforated to contain the screw;and the inside of the nut has aspiral groove, made to fit thespiral thread of the screw; justlike the lid of a box which screwson. The handle which projectsfrom the nut is a lever, withoutwhich, or something equivalent,the screw is never used as amechanical power. The nut,with a lever L attached to it, iscommonly called a winch. The power of the screw,complicated as it appears, is referable to one of themost simple of the mechanical powers, the inclinedplane. If a slip of paper be cut in the form of an.
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