The kilogram-force (kgf or kg_{F}), or kilopond (kp, from Latin: pondus, lit. 'weight'), is a non-standard gravitational metric unit of force. 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 of mass in a 9.80665 m/s^{2} gravitational field (standard gravity, a conventional value approximating the average magnitude of gravity on Earth).^{[1]} That is, it is the weight of a kilogram under standard gravity. 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.
kilogram-force | |
---|---|
Unit system | Gravitational metric system |
Unit of | Force |
Symbol | kgf |
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 |
Kilogram-force is a non-standard unit and is classified in the International System of Units (SI) as a unit that is not accepted for use with SI.^{[4]}
The gram-force and kilogram-force were never well-defined units until the CGPM adopted a standard acceleration of gravity of 9.80665 m/s^{2} for this purpose in 1901,^{[5]} 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.^{[6]} Instead, the newton was proposed in 1913^{[7]} and accepted in 1948.^{[8]} 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. It is still in use for some purposes, for example, it is used for the tension of bicycle spokes,^{[9]} for informal references to pressure in kilograms per square centimetre (1 kp/cm^{2}) 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, for the strength of bond wire in grams-force,^{[10]} and to define the "metric horsepower" (PS) as 75 metre-kiloponds per second.^{[2]} In addition, the kilogram force was the standard unit used for Vickers hardness testing.^{[11]}
Base | Force | Weight | Mass | ||
---|---|---|---|---|---|
2nd law of motion | m = F/a | F = W ⋅ a/g | F = m ⋅ a | ||
System | GM | M | CGS | MTS | SI |
Acceleration (a) | m/s^{2} | m/s^{2} | Gal | m/s^{2} | m/s^{2} |
Mass (m) | hyl | kilogram | gram | tonne | kilogram |
Force (F), weight (W) |
kilopond | kilopond | dyne | sthène | newton |
Pressure (p) | technical atmosphere | standard atmosphere | barye | pieze | pascal |
In 1940s, Germany, the thrust of a rocket engine was measured in kilograms-force,^{[citation needed]} in the Soviet Union it remained the primary unit for thrust in the Russian space program until at least the late 1980s.^{[citation needed]}
The term "kilopond" has been declared obsolete.^{[14]}
The 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.
newton | dyne | kilogram-force, kilopond |
pound-force | poundal | |
---|---|---|---|---|---|
1 N | ≡ 1 kg⋅m/s^{2} | = 10^{5} dyn | ≈ 0.10197 kp | ≈ 0.22481 lbf | ≈ 7.2330 pdl |
1 dyn | = 10^{–5} N | ≡ 1 g⋅cm/s^{2} | ≈ 1.0197×10^{−6} kp | ≈ 2.2481×10^{−6} lbf | ≈ 7.2330×10^{−5} pdl |
1 kp | = 9.80665 N | = 980665 dyn | ≡ g_{n} × 1 kg | ≈ 2.2046 lbf | ≈ 70.932 pdl |
1 lbf | ≈ 4.448222 N | ≈ 444822 dyn | ≈ 0.45359 kp | ≡ g_{n} × 1 lb | ≈ 32.174 pdl |
1 pdl | ≈ 0.138255 N | ≈ 13825 dyn | ≈ 0.014098 kp | ≈ 0.031081 lbf | ≡ 1 lb⋅ft/s^{2} |
The value of g_{n} as used in the official definition of the kilogram-force (9.80665 m/s^{2}) is used here for all gravitational units. |
The recommended tension for spokes in bicycle wheels can be as low as 80 Kilograms force (Kfg) and as high as 230 Kilograms force.
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.
In the past the units for Vickers hardness were kg/mm2; in Table 12.6 we use the SI units of GPa.