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The kilogram (also spelled kilogramme [1]) is the base unit of mass in the International System of Units (SI), having the unit symbol kg. [1] The word "kilogram" is formed from the combination of the metric prefix kilo-(meaning one thousand) and gram; [2] it is colloquially shortened to "kilo" (plural "kilos").
The International Prototype of the Kilogram (referred to by metrologists as the IPK or Le Grand K; sometimes called the ur-kilogram, [1] [2] or urkilogram, [3] particularly by German-language authors writing in English [3] [4]:30 [5]: 64 ) is an object whose mass was used to define the kilogram from 1889, when it replaced the Kilogramme des ...
The base units are defined in terms of the defining constants. For example, the kilogram is defined by taking the Planck constant h to be 6.626 070 15 × 10 −34 J⋅s, giving the expression in terms of the defining constants [1]: 131 1 kg = (299 792 458) 2 / (6.626 070 15 × 10 −34)(9 192 631 770) h Δν Cs / c 2 .
Scientists want to define the kilogram by gravity—and not just electricity. Here’s why correctly quantifying mass is more important than you think.
For example, in retail commerce, the "net weight" of products actually refers to mass, and is expressed in mass units such as grams or ounces (see also Pound: Use in commerce). Conversely, the load index rating on automobile tires, which specifies the maximum structural load for a tire in kilograms, refers to weight; that is, the force due to ...
The kilogram is the only standard unit to include an SI prefix (kilo-) as part of its name. 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 .
For example, if one takes exactly one kilogram of ice, and applies heat, the mass of the resulting melt-water will be more than a kilogram: it will include the mass from the thermal energy (latent heat) used to melt the ice; this follows from the conservation of energy. [36] This number is small but not negligible: about 3.7 nanograms.
Half-life: t 1/2: Time for a quantity to decay to half its initial value s T: Heat: Q: Thermal energy: joule (J) L 2 M T −2: Heat capacity: C p: Energy per unit temperature change J/K L 2 M T −2 Θ −1: extensive Heat flux density: ϕ Q: Heat flow per unit time per unit surface area W/m 2: M T −3: Illuminance: E v: Wavelength-weighted ...