mechanical engineering Mechanical engineering is the study of physical machines that may involve force and movement. It is an engineering branch that combines engineering physics and mathematics principles with materials science, to design, analyze, manufacture, ...

, mechanical efficiency is a dimensionless number that measures the effectiveness of a mechanism or

machine A machine is a physical system using power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolecul ...

in transforming the power input to the device to power output. A machine is a

mechanical linkage A mechanical linkage is an assembly of systems connected to manage forces and movement. The movement of a body, or link, is studied using geometry so the link is considered to be rigid. The connections between links are modeled as providing i ...

in which

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a ...

is applied at one point, and the force does work moving a load at another point. At any instant the power input to a machine is equal to the input force multiplied by the

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

of the input point, similarly the power output is equal to the force exerted on the load multiplied by the velocity of the load. The mechanical efficiency of a machine (often represented by the Greek letter

eta Eta (uppercase , lowercase ; grc, ἦτα ''ē̂ta'' or ell, ήτα ''ita'' ) is the seventh letter of the Greek alphabet, representing the close front unrounded vowel . Originally denoting the voiceless glottal fricative in most dialects, ...

\eta

) is a dimensionless number between 0 and 1 that is the ratio between the power output of the machine and the power input :

\eta = \frac

Since a machine does not contain a source of energy, nor can it store energy, from

conservation of energy In physics and chemistry, the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be ''conserved'' over time. This law, first proposed and tested by Émilie du Châtelet, means tha ...

the power output of a machine can never be greater than its input, so the efficiency can never be greater than 1. All real machines lose energy to

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of ...

; the energy is dissipated as heat. Therefore their power output is less than their power input :

\text = \text - \text

Therefore the efficiency of all real machines is less than 1. A

hypothetical A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obser ...

machine without friction is called an '' ideal machine'', such a machine would not have any energy losses, so its output power would equal its input power, and its efficiency would be 1. (100%) For

hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to produce electricity or to power machines. This is achieved by converting the gravitational potential or kinetic energy of ...

turbines the efficiency is referred to as hydraulic efficiency.IEC standard 60041

References

{{Reflist Mechanisms (engineering) Energy conversion he:נצילות מכנית

See also

References