Editing Mechanical efficiency

{{short description|Ratio of the output to input  power of a machine}}
{{More citations needed|date=July 2017}}

In [[mechanical engineering]], '''mechanical efficiency''' is a [[dimensionless ratio]] that measures the [[efficiency]] of a [[Mechanism (engineering)|mechanism]] or [[machine (mechanical)|machine]] in transforming the [[Power (physics)|power]] input to the device to power output.  A machine is a [[mechanical linkage]] in which [[force (physics)|force]] is applied at one point, and the force does [[work (physics)|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]] 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]] ''η'') is a dimensionless number between 0 and 1 that is the ratio between the power output of the machine and the power input<ref>{{cite web | title=Mechanical efficiency| website=Encyclopedia Britannica | date=2017-06-08 | url=https://www.britannica.com/technology/mechanical-efficiency | ref={{sfnref | Encyclopædia Britannica | 2017}} | access-date=2017-06-08}}</ref>

<math display="block">\eta = \frac{\text{Power output}}{\text{Power input}}</math>

Since a machine does not contain a source of energy, nor can it store energy, from [[conservation of energy]] 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]]; the energy is [[dissipated]] as heat.  Therefore, their power output is less than their power input

<math display="block">\text{Power output} = \text{Power input} - \text{Frictional power loss}</math>

Therefore, the efficiency of all real machines is less than 1.  A [[Idealization (philosophy of science)|hypothetical]] 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]] turbines the efficiency is referred to as hydraulic efficiency.<ref>{{Cite thesis|url=https://www.researchgate.net/publication/327305883|title = Continuous Efficiency Measurements on Hydro Power Plants |degree=PhD |year=2016 |first=Erik Jacques |last=Wiborg |location=Norway |publisher=Institutt for energi og prosessteknikk}}</ref><ref>IEC standard 60041</ref>

==See also==
* [[Mechanical advantage]]
* [[Thermal efficiency]]
* [[Electrical efficiency]]
* [[Internal combustion engine]]
* [[Electric motor]]
* [[Velocity ratio]]

==References==
{{Reflist}}

[[Category:Mechanisms (engineering)]]
[[Category:Energy conversion]]
[[Category:Mechanical quantities]]

[[he:נצילות מכנית]]