According to the German scientist Franz Reuleaux, a machine is defined as “a combination of resistant bodies arranged in a way that allows mechanical forces of nature to perform work accompanied by specific, predetermined motion.” In this context, the term “machine” is generally interpreted to mean a mechanism.
In engineering, a mechanism refers to a device that converts input forces and motion into a specific arrangement of output forces and motion. Mechanisms typically comprise moving parts, which can include:

  • Gears and gear trains
  • Belts and chain drives
  • Cams and followers
  • Friction devices like brakes or clutches
  • Structural components such as frames, fasteners, bearings, springs, or lubricants
  • Various machine elements like splines, pins, or keys.

A mechanism is typically a component within a larger process known as a mechanical system or machine. Occasionally, an entire machine may be referred to as a mechanism, such as the steering mechanism in a car or the winding mechanism of a wristwatch. However, generally, a group of multiple mechanisms is referred to as a machine.