Have you ever unscrewed the lid of a jar? Been cooled by a ceiling fan? Raised or lowered a piano stool?
Then you’ve seen the work of another simple machine, the screw. In a sense, though, the screw is not a simple machine. It’s actually an inclined plane wrapped around a cylinder with a wedge at the tip. Picture a typical screw. The wedge is the pointed end, and the inclined plane is the thread that wraps around the screw.
Simple or not, screws can do three jobs very well. They can move objects, press or crush them, and hold them down.
