# Kilogram-force

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### WIKIPEDIA ARTICLE

Kilogram-force
Unit system Gravitational metric system
Unit of Force
Symbol kgf
Unit conversions
1 kgf in ... ... is equal to ...
SI units    9.806650 N
CGS units    980,665.0 dyn
British Gravitational units    2.204623 lbf
Absolute English units    70.93164 pdl

The kilogram-force (kgf or kgF), or kilopond (kp, from Latin pondus meaning weight), is a gravitational metric unit of force. It is equal to the magnitude of the force exerted by one kilogram of mass in a 9.80665 m/s2 gravitational field (standard gravity, a conventional value approximating the average magnitude of gravity on Earth).[1] Therefore, one kilogram-force is by definition equal to 9.80665 N.[2][3] Similarly, a gram-force is 9.80665 mN, and a milligram-force is 9.80665 μN. One kilogram-force is approximately 2.204622 pound-force.

Kilogram-force is a non-standard unit and is classified in SI Metric System as a unit that is unacceptable for use with SI.[4]

## History

The gram-force and kilogram-force were never well-defined units until the CGPM adopted a standard acceleration of gravity of 980.665 cm/s2 for this purpose in 1901,[5] though they had been used in low-precision measurements of force before that time. 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.

Prior to this, the unit was widely used in much of the world and it is still in use for some purposes. The thrust of a rocket engine, for example, was measured in kilograms-force in 1940s Germany, in the Soviet Union (where it remained the primary unit for thrust in the Russian space program until at least the late 1980s), and it is still used today in China and sometimes by the European Space Agency.

The term "kilopond" has been declared obsolete[6] and should no longer be used.

It is also used for tension of bicycle spokes,[7] for informal references to pressure in kilograms per square centimeter (1 kp/cm2) which is the technical atmosphere (at) and very close to 1 bar and the standard atmosphere (atm), for the draw weight of bows in archery, and to define the "metric horsepower" (PS) as 75 metre-kiloponds per second.[2] In addition, kilograms force is the standard unit used for Vickers hardness testing.

Three approaches to metric units of mass and force or weight[8][9]
Base Force Weight Mass
2nd law of motion m = F/a F = Wa/g F = ma
System GM M CGS MTS SI
Acceleration (a) m/s2 m/s2 gal m/s2 m/s2
Mass (m) hyl kilogram gram tonne kilogram
Force (F),
weight (W)
kilopond kilopond dyne sthène newton
Pressure (p) technical atmosphere atmosphere barye pieze pascal

## Related units

The tonne-force, metric ton-force, megagram-force, and megapond (Mp) are each 1000 kilograms-force.

The decanewton or dekanewton (daN) is used in some fields as an approximation to the kilogram-force, being exactly rather than approximately 10 newtons.

Units of force
newton
(SI unit)
dyne kilogram-force,
kilopond
pound-force poundal
1 N ≡ 1 kg⋅m/s2 = 105 dyn ≈ 0.10197 kp ≈ 0.22481 lbf ≈ 7.2330 pdl
1 dyn = 10−5 N ≡ 1 g⋅cm/s2 ≈ 1.0197 × 10−6 kp ≈ 2.2481 × 10−6 lbf ≈ 7.2330 × 10−5 pdl
1 kp = 9.80665 N = 980665 dyn gn⋅(1 kg) ≈ 2.2046 lbf ≈ 70.932 pdl
1 lbf ≈ 4.448222 N ≈ 444822 dyn ≈ 0.45359 kp gn⋅(1 lb) ≈ 32.174 pdl
1 pdl ≈ 0.138255 N ≈ 13825 dyn ≈ 0.014098 kp ≈ 0.031081 lbf ≡ 1 lb⋅ft/s2
The value of gn as used in the official definition of the kilogram-force is used here for all gravitational units.

## References

1. ^ The international system of units (SI)United States Department of Commerce, NIST Special Publication 330, 2008, p. 52
2. ^ a b NIST Guide for the Use of the International System of Units (SI) Special Publication 811, (1995) page 51
3. ^ BIPM SI brochure Archived 2004-06-15 at the Wayback Machine., chapter 2.2.2.
4. ^ NIST Guide to the SI, Chapter 5: Units Outside the SI
5. ^ Resolution of the 3rd CGPM (1901)
6. ^ European Economic Community, Council Directive of 18 October 1971 on the approximation of the laws of the Member States relating to units of measurement (Directive 71/354/EEC), Annex, Chapter III.
7. ^ Park Tool. "Balancing wheel tension with the TM-1 Spoke Tension Meter". Cyclingnews. Retrieved 2013-09-03. The recommended tension for spokes in bicycle wheels can be as low as 80 Kilograms force (Kfg) and as high as 230 Kilograms force.
8. ^ Comings, E. W. (1940). "English Engineering Units and Their Dimensions". Industrial & Engineering Chemistry. 32 (7): 984–987. doi:10.1021/ie50367a028.
9. ^ Klinkenberg, Adrian (1969). "The American Engineering System of Units and Its Dimensional Constant gc". Industrial & Engineering Chemistry. 61 (4): 53–59. doi:10.1021/ie50712a010.

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