Moving parts

[citation needed] Moving parts also do not include any mechanical locks, switches, nuts and bolts, screw caps for bottles etc.

A system with no moving parts is described as "solid state"[citation needed].

The amount of moving parts in a machine is a factor in its mechanical efficiency.

[4] Conversely, the fewer the number of moving parts, the greater the efficiency.

An electrical transformer, for example, has no moving parts, and its mechanical efficiency is generally above the 90% mark.

)[5] Two means are used for overcoming the efficiency losses caused by friction between moving parts.

Second, the moving parts of a machine are designed so that they have a small amount of contact with one another.

)[6] The scientific and engineering discipline that deals with the lubrication, friction, and wear of moving parts is tribology, an interdisciplinary field that encompasses materials science, mechanical engineering, chemistry, and mechanics.

[8] Other concerns that lead to failure include corrosion,[8] erosion,[8] thermal stress and heat generation,[8] vibration,[8] fatigue loading,[8] and cavitation.

Fatigue is related to large inertial forces, and is affected by the type of motion that a moving part has.

[8] One final, particular, factor related to failure of moving parts is kinetic energy.

For example, consider a stone caught on the blades of a fan or propeller, or even the proverbial "spanner/monkey wrench in the works".

A machine with moving parts can, mathematically, be treated as a connected system of bodies, whose kinetic energies are simply summed.

[9] The kinetic energy of rotation of the moving parts can be determined by noting that every such system of moving parts can be reduced to a collection of connected bodies rotating about an instantaneous axis, which form either a ring or a portion of an ideal ring, of radius

, also expressible if the ring is modelled as a collection of discrete particles as the sum of the products of those mass and the squares of their radii

is the angular velocity of the moving parts about the same axis as the moment of inertia.

This gives the formula for the total kinetic energy of the moving parts of a machine as

[9][10] In technical drawing, moving parts are, conventionally, designated by drawing the solid outline of the part in its main or initial position, with an added outline of the part in a secondary, moved, position drawn with a phantom line (a line comprising "dot-dot-dash" sequences of two short and one long line segments) outline.

[14] In recent decades, the use of animation has become more practical and widespread in technical and engineering diagrams for the illustration of the motions of moving parts.

Animation represents moving parts more clearly and enables them and their motions to be more readily visualized.