Screw (simple machine)

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A screw is one of the six simple machines. All screws are helical inclined planes. 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. More threading increases the mechanical advantage. A rough comparison of mechanical advantage can be done by taking the circumference of the shaft of the screw and divide by the distance between the threads.

A screw is a shaft with a helical groove or thread formed on its surface and provision at one end to turn the screw. Its main uses are as a threaded fastener used to hold objects together, and as a simple machine used to translate torque into linear force. It can also be defined as an inclined plane wrapped around a shaft.

Screws come in a variety of shapes and sizes for different purposes.

Thread as found on a screw.

[edit] Mechanical advantage

The mechanical advantage of a screw without using a screwdriver is:

• P = Pitch of screw (The distance between two adjacent screw threads is called the pitch.)
• C = Circumference of the head

MA = C / P.

The same formula can be used when using a screwdriver, but with:

• C = Circumference of the screwdriver handle.

[edit] Examples

• Lead screw and ball screw are specialized screws for translating rotational to linear motion.
• 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.
• Archimedes' screws and worm gears are examples of this machine.

[edit] See also

• Screw (disambiguation)
• Screw - the threaded fastener
• Archimedes' screw