Model: 004 The Screw
From the point of view of the mechanic, the screw is simply an inclined plane wrapped around a cylinder. The vise and letter-press are examples of the screw whose purpose is to obtain increased pressure. Another example, the jackscrew, is used by builders to lift heavy objects with the least effort. The propellers of boats and airplanes are further examples.
[Virginia Downward & William M. Clark, 1930]

[Editor's Note: The screw is considered one of the so-called simple machines described in Aristotle's MHXANIKA or Mechanical Problems, probably written by his students c. 300 BCE. The 'simple' machine concept is based on the idea of machines as force transformation devices. This view of the machine was replaced by the Paris school of kinematics in the Ecole Polytechnique around 1800. A machine is viewed as a motion changing device. In Reuleaux's scheme, the 'simple machines' are parts of kinematic mechanisms or machine elements. However the 'simple machine' concept still persists in elementary school texts on machines and physics in the USA. See also the Reuleaux-Voigt models A-1, M-1, M-2, M-3. The screw was called by Reuleaux a lower pair. The constraint is by surface contact between the two parts. FCM]

Francis Moon 2005-00-00