Screw (simple machine)

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A screw is one of the six simple machines. A simple screw is a helical inclined plane. A screw can convert a rotational force (torque) to a linear force and vice versa. The ratio of threading determines the mechanical advantage of the machine.

[edit] Examples

Automated garage door, where a motor drives a long finely threaded shaft at relatively high speed and lifts the heavy door at a slower rate
Rack and pinion, where the pinion is turned by the steering wheel and pulls the rack to turn a heavy vehicle
Archimedes' screws and worm gears are examples of this machine.