Thegravitational metric system (original French termSystème des Méchaniciens) is a non-standard system of units, which does not comply with theInternational System of Units (SI). It is built on the threebase quantitieslength,time andforce withbase unitsmetre,second andkilopond respectively. Internationally used abbreviations of the system areMKpS,MKfS orMKS (from Frenchmètre–kilogramme-poids–seconde ormètre–kilogramme-force–seconde).[1]However, the abbreviation MKS is also used for theMKS system of units, which, like the SI, usesmass inkilogram as a base unit.
Nowadays, the mass as a property of an object and its weight, which depends on the gravity of the Earth at its position are strictly distinguished. However historically, the kilopond was also called kilogram, and only later the kilogram-mass (today's kilogram) was separated from the kilogram-force (today's kilopond). A kilopond originally referred to the weight of a mass of one kilogram. Since the gravitational acceleration on the surface of the Earth can differ, one gets different values for the unit kilopond and its derived units at different locations. To avoid this, the kilopond was first defined at sea level and alatitude of 45 degrees, since 1902 via thestandard gravity of9.80665 m/s2.[2]
Further disadvantages are inconsistencies in the definition of derived units such ashorsepower (1 PS = 75 kp⋅m/s) and the missing link to electric, magnetic or thermodynamic units.[1]
In Germany, the kilopond lost its legal status as a unit of force on 1 January 1978, when for legal purposes the SI unit system was adopted.[3] A kilopond can be converted to the SI unitnewton by multiplication with the standard accelerationgn:
In English contexts the unit of force is usually formed by simply appending the suffix "force" to the name of the unit of mass, thusgram-force (gf) orkilogram-force (kgf), which follows the tradition ofpound-force (lbf). In other, international, contexts the special namepond (p) orkilopond (kp) respectively is more frequent.
The hyl, metricslug (mug), or TME (German:technische Masseneinheit,lit. 'technical mass unit'), is the mass that accelerates at 1 m/s2 under a force of 1 kgf.[4] The unit, long obsolete,[5] has also been used as the unit of mass in a metre–gram-force–second (mgfs) system.[6]
The gravitational unit of pressure is thetechnical atmosphere (at). It is the gravitational force of one kilogram, i.e. 1 kgf, exerted on an area of one square centimetre.
There is no dedicated name for the unit of energy, "metre" is simply appended to "kilopond", but usually the symbol of the kilopond-metre is written without the middle dot.
In 19th-century France there was as a unit of power, theponcelet, which was defined as the power required to raise a mass of 1quintal (1 q = 100 kg) at a velocity of 1 m/s. The German or metrichorsepower (PS,Pferdestärke) is arbitrarily selected to be three quarters thereof.