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The Screw

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-109

2025-12-22

1145

consists of a cylinder of wood or metal about which is a thread. If the cross section of this thread is square, the thread is called a square thread; if triangular, it is called a V-thread. A good model of a square-thread screw can be made by winding a long strip of leather in a spiral around a wooden cylinder, and tacking it fast. That the screw is a modified inclined plane may be seen by cutting a right-angled triangle out of paper and winding it about a pencil as in Fig.1.It will be seen that the hypotenuse, which represents the length of an inclined plane, forms the spiral thread of the screw. If CB is taken equal to the circumference of the pencil, then AB will be equal to the distance between the threads DE. This distance is called the pitch, and determines how far the screw (or the resistance) moves at each revolution. The power is generally applied to a screw at the end of a lever, as the handle of a wrench.

FIG. 1.- Screws

 It is applied either to the screw or to the nut, as in bolting two pieces of wood together.

FIG.2.