, from latin pondus
), is a gravitational metric unit of force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
. It is equal to the magnitude of the force exerted by one kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
in a gravitational field (standard gravity
Standard gravity, or standard acceleration due to free fall, usually denoted by g0 or gn, is the nominal acceleration of an object in a vacuum near the surface of the Earth. It is defined as precisely , or about...
, a conventional value approximating the average magnitude of gravity on Earth). Therefore one kilogram-force is by definition equal to . Similarly, a gram-force is , and a milligram-force is .
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
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups 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
A spoke is one of some number of rods radiating from the center of a wheel , connecting the hub with the round traction surface....
, for torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
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
A technical atmosphere is a non-SI unit of pressure equal to one kilogram-force per square centimeter.The symbol "at" clashes with that of the katal , the SI unit of catalytic activity; a kilotechnical atmosphere would have the symbol "kat", indistinguishable from the symbol for the katal...
(at) as 1 kilopond per square centimetre.
, metric ton-force
, or megapond
) are 1000 kilograms-force.
) is used in some fields as an approximation to the kilogram-force, being exactly rather than approximately 10 newtons.