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Gravitational "weight" is the force created when a mass is acted upon by a gravitational field and the object is not allowed to free-fall, but is supported or retarded by a mechanical force, such as the surface of a planet. Such a force constitutes weight. [2] This force can be added to by any other kind of force.
The most common definition of weight found in introductory physics textbooks defines weight as the force exerted on a body by gravity. [1] [12] This is often expressed in the formula W = mg, where W is the weight, m the mass of the object, and g gravitational acceleration.
If a first body of mass m A is placed at a distance r (center of mass to center of mass) from a second body of mass m B, each body is subject to an attractive force F g = Gm A m B /r 2, where G = 6.67 × 10 −11 N⋅kg −2 ⋅m 2 is the "universal gravitational constant". This is sometimes referred to as gravitational mass.
This is convenient because one pound mass exerts one pound force due to gravity. Note, however, unlike the other systems the force unit is not equal to the mass unit multiplied by the acceleration unit [11] —the use of Newton's second law, F = m ⋅ a, requires another factor, g c, usually taken to be 32.174049 (lb⋅ft)/(lbf⋅s 2).
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. The unit is in common use for masses above about 10 3 kg and is often used with SI prefixes.
[citation needed] The kilogram-force is equal to the magnitude of the force exerted on one kilogram of mass in a 9.806 65 m/s 2 gravitational field (standard gravity, a conventional value approximating the average magnitude of gravity on Earth). [2] That is, it is the weight of a kilogram under standard gravity. One kilogram-force is defined as ...
The apparent weight can also differ from weight when an object is "partially or completely immersed in a fluid", where there is an "upthrust" from the fluid that is working against the force of gravity. [2] Another example is the weight of an object or person riding in an elevator.
Kilogram-force – Weight on earth of a one-kilogram mass; Mass versus weight – Distinction between mass and weight; Metric system – Decimal-based systems of measurement with 7 base units defined by physical constants; National Institute of Standards and Technology – Measurement standards laboratory in the United States (NIST) Newton ...