Editing Kilogram-force

{{Short description|Weight on earth of a one-kilogram mass}}
{{hatnote group|{{redirect|kgf||KGF (disambiguation)}}{{redirect-distinguish|Kilopond|Kilopound}}}}
{{Infobox unit
| bgcolor      = 
| name         = kilogram-force
| image        = 
| caption      = 
| standard     = [[Gravitational metric system]]
| quantity     = [[Force]]
| symbol       = kgf
| symbol2      = 
| extralabel   = 
| extradata    = 
| units1 = SI units
| inunits1     = {{convert|1|kgf|N|sigfig=7|disp=out}}
| units2 = CGS units
| inunits2     = {{convert|1|kgf|dyn|sigfig=7|disp=out}}
| units3 = British Gravitational units
| inunits3     = {{convert|1|kgf|lbf|sigfig=7|disp=out}}
| units4 = Absolute English units
| inunits4     = {{convert|1|kgf|pdl|sigfig=7|disp=out}}
}}
The '''kilogram-force''' ('''kgf''' or '''kg<sub>F</sub>'''), or '''kilopond''' ('''kp''', from {{langx|la|pondus|lit=weight}}), is a non-standard [[Gravitational metric system|gravitational metric]] unit of [[force]]. It is not accepted for use with the International System of Units (SI)<ref>[https://www.nist.gov/pml/nist-guide-si-chapter-5-units-outside-si NIST Guide to the SI, Chapter 5: Units Outside the SI]</ref> and is deprecated for most uses.{{fact|date=February 2024}} The kilogram-force is equal to the magnitude of the force exerted on one [[kilogram]] of [[mass]] in a {{val|9.80665|u=m/s2}} gravitational field ([[standard gravity]], a conventional value approximating the average magnitude of gravity on Earth).<ref>[http://physics.nist.gov/Pubs/SP330/sp330.pdf ''The international system of units (SI)''] {{Webarchive|url=https://web.archive.org/web/20160603215953/http://physics.nist.gov/Pubs/SP330/sp330.pdf |date=2016-06-03 }} – [[United States Department of Commerce]], [[National Institute of Standards and Technology|NIST]] Special Publication 330, 2008, p. 52</ref> That is, it is the [[weight]] of a kilogram under standard gravity. One kilogram-force is defined as {{val|9.80665|ul=N}}.<ref name=SP811>[[NIST]] [http://physics.nist.gov/Pubs/SP811/appenB8.html#K ''Guide for the Use of the International System of Units (SI)''] Special Publication 811, (1995) page 51</ref><ref>[http://www1.bipm.org/en/si/si_brochure/chapter2/2-2/2-2-2.html BIPM SI brochure] {{webarchive|url=https://web.archive.org/web/20040615185954/http://www1.bipm.org/en/si/si_brochure/chapter2/2-2/2-2-2.html |date=2004-06-15 }}, chapter 2.2.2.</ref> Similarly, a gram-force is {{val|9.80665|u=mN}}, and a milligram-force is {{val|9.80665|u=uN}}.

==History==
The gram-force and kilogram-force were never well-defined units until the [[CGPM]] adopted a ''standard acceleration of gravity'' of 9.80665&nbsp;m/s<sup>2</sup> for this purpose in 1901,<ref>[https://www.bipm.org/en/committees/cg/cgpm/3-1901 Resolution of the 3rd CGPM (1901)]</ref> though they had been used in low-precision measurements of force before that time. Even then, the proposal to define kilogram-force as a standard unit of force was explicitly rejected.<ref name="CGPM3-P62">[https://www.bipm.org/utils/common/pdf/CGPM/CGPM3.pdf#page=62 Proceedings of the 3rd General Conference on Weights and Measures], 1901, pages 62–64 and 68, (french)</ref> Instead, the ''[[Newton (unit)|newton]]'' was proposed in 1913<ref name="CGPM5-p51">[https://www.bipm.org/utils/common/pdf/CGPM/CGPM5.pdf#page=51 Proceedings of the 5th General Conference on Weights and Measures], 1913, pages 51 and 56, (french)</ref> and accepted in 1948.<ref name="CGPM9-7">{{Cite web |url=https://www.bipm.org/en/CGPM/db/9/7/ |title=Resolution 7 of the 9th meeting of the CGPM (1948) |access-date=2021-03-02 |archive-date=2020-06-22 |archive-url=https://web.archive.org/web/20200622105030/https://www.bipm.org/en/CGPM/db/9/7/ |url-status=dead }}</ref>
The kilogram-force has never been a part of the [[International System of Units]] (SI), which was introduced in 1960. The SI unit of force is the [[Newton (unit)|newton]].

Prior to this, the units were widely used in much of the world. They are still in use for some purposes; for example, they are used to specify tension of bicycle [[spoke]]s,<ref>{{cite web|url=http://ftp.cyclingnews.com/tech/fix/?id=tm_1|title=Balancing wheel tension with the TM-1 Spoke Tension Metre|quote=The recommended tension for spokes in bicycle wheels can be as low as 80 Kilograms force (Kfg) and as high as 230 Kilograms force. Author=Park Tool|author-link=Park Tool|publisher=Cyclingnews|access-date=2013-09-03}}</ref> [[draw weight]] of bows in [[archery]], and tensile strength of [[bond wire|electronics ''bond wire'']],<ref>{{Cite book |last=Harman |first=George G. |url=https://www.worldcat.org/oclc/609421363 |title=Wire Bonding in Microelectronics |date=2010 |publisher=McGraw-Hill |isbn=978-0-07-164265-1 |edition=3rd |location=New York |pages=408 |oclc=609421363 |quote=Breaking load (BL): The strength of a wire and its actual force (usually given in grams, grams-force, mN, etc.) required to break a particular wire in a tensile pull. It is not tensile strength, which by definition is the force per unit area.}}</ref> for informal references to pressure (as the technically incorrect ''kilogram per square centimetre'', omitting ''-force'', the kilogram''-force'' per square centimetre being the ''[[technical atmosphere]]'', the value of which is very near those of both the ''[[bar (unit)|bar]]'' and the ''standard atmosphere''), and to define the "[[metric horsepower]]" (PS) as 75 metre-kiloponds per second.<ref name="SP811"/> In addition, the kilogram force was the standard unit used for [[Vickers hardness test]]ing.<ref>{{Cite book |last=Callister |first=William D. Jr. |url=https://www.worldcat.org/oclc/401168960 |title=Materials Science and Engineering: An Introduction. |date=2010 |publisher=John Wiley & Sons, Inc. |others=David G. Rethwisch |isbn=978-0-470-41997-7 |edition=8th |location=Hoboken, NJ |oclc=401168960 |quote=In the past the units for Vickers hardness were kg/mm2; in Table 12.6 we use the SI units of GPa.}}</ref>
{{GravEngAbs|system=metric}}

In 1940s, Germany, the thrust of a rocket engine was measured in kilograms-force,{{citation needed|date=September 2020}} in the Soviet Union it remained the primary unit for thrust in the Russian space program until at least the late 1980s.{{citation needed|date=September 2020}} Dividing the thrust in kilograms-force on the mass of an engine or a rocket in kilograms conveniently gives the [[thrust to weight ratio]], dividing the thrust on propellant consumption rate ([[mass flow rate]]) in kilograms per second gives the [[specific impulse]] in seconds.

The term "kilopond" has been declared obsolete.<ref>European Economic Community, Council Directive of 18 October 1971 on the approximation of the laws of the Member States relating to units of measurement</ref>

== Related units ==
The '''[[Ton-force#Tonne-force|tonne-force]]''', '''metric ton-force''', '''megagram-force''', and '''megapond''' ('''Mp''') are each 1000 kilograms-force.

The '''decanewton''' or '''dekanewton''' ('''daN'''), exactly 10 N, is used in some fields as an approximation to the kilogram-force, because it is close to the 9.80665 N of 1 kgf.

The gram-force is {{Fraction|1|1000}} of a kilogram-force.
{{Units of force}}

==See also==
* [[Metrology]]
* [[Avoirdupois]]

== References ==
{{Reflist}}

[[Category:Units of force]]
[[Category:Non-SI metric units]]