The screw is really just an inclined plane wrapped around a shaft. To visualize this, cut a piece of paper in half diagonally and put magic marker on the cut edge (the hypotenuse). This is an image of a hypotenuse. Now wrap the paper around a pencil, beginning with a flat edge. When the screw is turned on its axis, material rides up the threads, and rotational motion is transformed into a back and forth motion.
Example of screws:
©2001 Jeff Goodman
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