The kilogram-force (kgf or kg_F), or kilopond (kp, from la, pondus, lit=weight), is a non-standard gravitational metric unit of

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 ...

. It does not comply with the International System of Units (SI) and is deprecated for most uses. The kilogram-force is equal to the magnitude of the force exerted on one

kilogram The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. ...

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different ele ...

in a gravitational field (

standard gravity The standard acceleration due to gravity (or standard acceleration of free fall), sometimes abbreviated as standard gravity, usually denoted by or , is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. ...

, a conventional value approximating the average magnitude of gravity on Earth). That is, it is the

weight In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar qua ...

of a kilogram under standard gravity. Therefore, one kilogram-force is by definition equal to .

NIST The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical sci ...

br>''Guide for the Use of the International System of Units (SI)''
Special Publication 811, (1995) page 51 Similarly, a gram-force is , and a milligram-force is . Kilogram-force is a non-standard unit and is classified in the

International System of Units The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. ...

(SI) as a unit that is not accepted for use with SI.

History

The gram-force and kilogram-force were never well-defined units until the

CGPM The General Conference on Weights and Measures (GCWM; french: Conférence générale des poids et mesures, CGPM) is the supreme authority of the International Bureau of Weights and Measures (BIPM), the intergovernmental organization established i ...

adopted a ''standard acceleration of gravity'' of 9.80665 m/s² for this purpose in 1901, though they had been used in low-precision measurements of force before that time. Even then, the proposal to define kilogram-force as standard unit of force was explicitly rejected.Proceedings of the 3rd General Conference on Weights and Measures
1901, pages 62–64 and 68, (french) Instead, the '' newton'' was proposed in 1913Proceedings of the 5th General Conference on Weights and Measures
1913, pages 51 and 56, (french) and accepted in 1948.Resolution 7 of the 9th meeting of the CGPM (1948)
/ref> The kilogram-force has never been a part of the

(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. It is still in use for some purposes, for example, it is used for the tension of bicycle

spoke A spoke is one of some number of rods radiating from the center of a wheel (the hub where the axle connects), connecting the hub with the round traction surface. The term originally referred to portions of a log that had been riven (split ...

s, for informal references to pressure in kilograms per square centimetre (1 kp/cm²) which is the

technical atmosphere Technical may refer to: * Technical (vehicle), an improvised fighting vehicle * Technical analysis, a discipline for forecasting the future direction of prices through the study of past market data * Technical drawing, showing how something is co ...

(at) and very close to 1

bar Bar or BAR may refer to: Food and drink * Bar (establishment), selling alcoholic beverages * Candy bar * Chocolate bar Science and technology * Bar (river morphology), a deposit of sediment * Bar (tropical cyclone), a layer of cloud * Bar ( ...

and the standard atmosphere (atm), for the draw weight of bows in archery, for the strength of

bond wire Bond or bonds may refer to: Common meanings * Bond (finance), a type of debt security * Bail bond, a commercial third-party guarantor of surety bonds in the United States * Chemical bond, the attraction of atoms, ions or molecules to form chemical ...

in grams-force, and to define the "

metric horsepower Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are the ...

" (PS) as 75 metre-kiloponds per second. In addition, the kilogram force was the standard unit used for

Vickers hardness test The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness ...

ing. In 1940s, Germany, the thrust of a rocket engine was measured in kilograms-force, in the Soviet Union it remained the primary unit for thrust in the Russian space program until at least the late 1980s. The term "kilopond" has been declared obsolete.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.

Related units

The

tonne-force A ton-force is one of various units of force defined as the weight of one ton due to standard gravity.All calculations on this page assume the following definition of standard gravity, ''g''0. :''g''0 = The precise definition depends on the defini ...

, 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.

References

{{Reflist Units of force Non-SI metric units

History

Related units

See also

References