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In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume, [2] although this is scientifically inaccurate – this quantity is more specifically called specific weight. For a pure substance the density has the same numerical value as its mass concentration.
Thus the kilogram-force is defined as precisely 9.80665 newtons. In reality, gravitational acceleration (symbol: g) varies slightly with latitude, elevation and subsurface density; these variations are typically only a few tenths of a percent. See also Gravimetry. Engineers and scientists understand the distinctions between mass, force, and weight.
The specific weight, also known as the unit weight (symbol γ, the Greek letter gamma), is a volume-specific quantity defined as the weight W divided by the volume V of a material: = / Equivalently, it may also be formulated as the product of density, ρ, and gravity acceleration, g: = Its unit of measurement in the International System of Units (SI) is newton per cubic metre (N/m 3), with ...
Mass fraction can also be expressed, with a denominator of 100, as percentage by mass (in commercial contexts often called percentage by weight, abbreviated wt.% or % w/w; see mass versus weight). It is one way of expressing the composition of a mixture in a dimensionless size ; mole fraction (percentage by moles , mol%) and volume fraction ...
In practice, this "amount of matter" definition is adequate for most of classical mechanics, and sometimes remains in use in basic education, if the priority is to teach the difference between mass from weight.) [23] This traditional "amount of matter" belief was contradicted by the fact that different atoms (and, later, different elementary ...
Since the density of dry air at 101.325 kPa at 20 °C is [10] 0.001205 g/cm 3 and that of water is 0.998203 g/cm 3 we see that the difference between true and apparent relative densities for a substance with relative density (20 °C/20 °C) of about 1.100 would be 0.000120. Where the relative density of the sample is close to that of water (for ...
A panel of global experts explains why BMI is not the most helpful measurement of body weight, and how else doctors can diagnose obesity. Image credit: VICTOR TORRES/Stocksy.
The notation common with mass density underlines the connection between the two quantities (the mass concentration being the mass density of a component in the solution), but it can be a source of confusion especially when they appear in the same formula undifferentiated by an additional symbol (like a star superscript, a bolded symbol or varrho).