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, 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.
It is also used for tension of bicycle spokes, for torque measured in "meter-kilograms", for informal references to pressure in kilograms per square centimeter (1 kp/cm² = 1 at ≈ 1 bar ≈ 1 atm), for the draw weight of bows in archery, and to define the "metric horsepower" (PS) as 75 metre-kiloponds per second or the technical atmosphere (at) as 1 kilopond per square centimetre.
| Base | force, length, time | weight, length, time | mass, length, time | |||||
|---|---|---|---|---|---|---|---|---|
| Force (F) | F = m·a = w·a/g | F = m·a/gc = w·a/g | F = m·a = w·a/g | |||||
| Weight (w) | w = m·g | w = m·g/gc ≈ m | w = m·g | |||||
| System | BG | GM | EE | M | AE | CGS | MTS | SI |
| Acceleration (a) | ft/s2 | m/s2 | ft/s2 | m/s2 | ft/s2 | Gal | m/s2 | m/s2 |
| Mass (m) | slug | hyl | lbm | kg | lb | g | t | kg |
| Force (F) | lb | kp | lbF | kp | pdl | dyn | sn | N |
| Pressure (p) | lb/in2 | at | PSI | atm | pdl/ft2 | Ba | pz | Pa |
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