Specific quantity

In the natural sciences, including physiology and engineering, the qualifier '''''specific''''' or '''''massic''''' typically indicates an intensive quantity obtained by dividing an extensive quantity of interest by ''mass''.<ref name="ISO80000-1">{{cite web | title=ISO 80000-1: Quantities and units – Part 1: General | website=iso.org | url=https://www.iso.org/obp/ui/#iso:std:iso:80000:-1:ed-2:v1:en | ref={{sfnref | iso.org}} | access-date=2023-10-16}}</ref><ref name="IUPACgreen">{{cite book | url=http://media.iupac.org/publications/books/gbook/IUPAC-GB3-2ndPrinting-Online-22apr2011.pdf | title=IUPAC Green Book | publisher=IUPAC and RSC Publishing | author=Cohen, E. R. | author-link=Quantities, Units and Symbols in Physical Chemistry | year=2007 | location=Cambridge | pages=6 (20 of 250 in PDF file) | isbn=978-0-85404-433-7 | edition=3rd|display-authors=etal}}</ref> For example, specific leaf area is leaf area divided by leaf mass. Derived SI units involve reciprocal kilogram (kg−1), e.g., square metre per kilogram (m2⋅kg−1); the expression "per unit mass" is also often used.

In some fields, like acoustics, "specific" can mean division by a quantity other than mass.<ref name="ISO80000-1" />

Named and unnamed specific quantities are given for the terms below.

== List ==

=== Mass-specific quantities === Per unit of mass (short form of ''mass-specific''): * Specific absorption rate, power absorbed per unit mass of tissue at a given frequency * Specific activity, radioactivity in becquerels per unit mass * Specific energy, defined as energy per unit mass ** Specific internal energy, internal energy per unit mass ** Specific kinetic energy, kinetic energy of an object per unit of mass * Specific enthalpy, enthalpy per unit mass * Specific enzyme activity, activity per milligram of total protein * Specific force, defined as the non-gravitational force per unit mass * Specific heat capacity, heat capacity per unit mass, unless another unit is named, such as mole-specific heat capacity, or volume-specific heat capacity * Specific latent heat, latent heat per unit mass * Specific leaf area, leaf area per unit dry leaf mass * Specific modulus, a materials property consisting of the elastic modulus per mass density of a material * Specific orbital energy, orbital energy per unit mass * Specific power, per unit of mass (or volume or area) * Specific relative angular momentum, of two orbiting bodies is angular momentum divided by the reduced mass, or the cross product of the relative position and the relative velocity * Specific surface area, per unit of mass, volume, or cross-sectional area * Specific volume, volume per unit mass, i.e. the reciprocal of density * {{anchor|Mass ratio}}'''Mass ratio''', "ratio by mass", mass per unit mass, massic mass or specific mass: the ratio of two mass values (in kilogram per kilogram)

=== Examples of other uses === Per unit of other types. * Brake-specific fuel consumption, fuel consumption per unit of braking power * Thrust-specific fuel consumption, fuel consumption per unit of thrust * Specific acid catalysis, in which the reaction rate is proportional to the concentration of the protonated solvent molecules * Specific acoustic impedance, ratio of sound pressure to particle speed at a single frequency * Specific capacity of a water well, quantity of water produced per (length) unit of drawdown * Specific detectivity of a photodetector * Specific gas constant, per molar mass * Specific gravity, also called relative density, is a dimensionless quantity defined as the ratio of the density (mass divided by volume) of a substance to the density of a given reference material * Specific humidity, mass of water vapour per unit mass dry air * Specific impulse, impulse (momentum change) per unit mass of propellant * Specific modulus, elastic modulus per mass density * Specific speed, unitless figure of merit{{clarify|date=July 2023}} used to classify pump impellers (pump-specific) and turbines (turbine-specific). Ratio of performance against reference pump that needs one unit of speed to pump one unit volume per one unit hydraulic head pressure. For a turbine, it is performance measured against a reference turbine that develops one unit of power per one unit speed per one unit of hydraulic head. * Specific storage, specific yield, and specific capacity, quantify the capacity of an aquifer to release groundwater from storage per unit decline in hydraulic head pressure * Specific strength, material strength (pressure required at failure) per unit material density * Specific surface area, per unit of mass, volume, or cross-sectional area * Specific thrust, thrust per unit mass of air intake rate

== See also == * {{slink|Intensive and extensive properties#Specific properties}} * Areic quantity * Lineic quantity * Molar quantity * Volumic quantity

== References == {{reflist}}

Category:Physical quantities Category:Intensive quantities Category:Quotients