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Because mass and weight are separate quantities, they have different units of measure. In the International System of Units (SI), the kilogram is the basic unit of mass, and the newton is the basic unit of force. The non-SI kilogram-force is also a unit of force typically used in the measure of weight.
The undecimogramme is a unit of mass equal to ten picograms (10 pg). The gamma (γ) is a unit of mass equal to one microgram (1 μg). The gravet is a unit of mass equal to one gram (1 g). The grave is a unit of mass equal to one kilogram (1 kg). The bar is a unit of mass equal to one megagram (1 Mg).
The SI base unit of mass is the kilogram (kg). In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but ...
Other units of mass are defined in terms of it. The avoirdupois pound is legally defined as a measure of mass, [25] but the name pound is also applied to measures of force. For instance, in many contexts, the pound avoirdupois is used as a unit of mass, but in some contexts, the term "pound" is used to refer to "pound-force".
The gram (10 −3 kg) is an SI derived unit of mass. However, the names of all SI mass units are based on gram, rather than on kilogram; thus 10 3 kg is a megagram (10 6 g), not a *kilokilogram. The tonne (t) is an SI-compatible unit of mass equal to a megagram (Mg), or 10 3 kg.
[8] [21] For example, most people would say that an object "weighs one kilogram", even though the kilogram is a unit of mass. The distinction between mass and weight is unimportant for many practical purposes because the strength of gravity does not vary too much on the surface of the Earth.
The kilogram is the only coherent SI unit whose name and symbol include a prefix. For historical reasons, the names and symbols for multiples and sub-multiples of the unit of mass are formed as if the gram were the base unit. Prefix names and symbols are attached to the unit name gram and the unit symbol g respectively.
The avoirdupois units of mass and weight differ for units larger than a pound (lb). The British imperial system uses a stone of 14 lb, a long hundredweight of 112 lb and a long ton of 2,240 lb. The stone is not a measurement of weight used in the US. The US customary system uses the short hundredweight of 100 lb and short ton of 2,000 lb.