A screw is one of the six simple machines. All screws are helicalinclined 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.
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.
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.
