In the

natural sciences Natural science is one of the branches of science concerned with the description, understanding and prediction of natural phenomena, based on empirical evidence from observation and experimentation. Mechanisms such as peer review and repeatab ...

, including

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

and

engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad rang ...

, a specific quantity generally refers to an

intensive quantity Physical properties of materials and systems can often be categorized as being either intensive or extensive, according to how the property changes when the size (or extent) of the system changes. According to IUPAC, an intensive quantity is on ...

obtained by dividing an

extensive quantity Physical properties of materials and systems can often be categorized as being either intensive or extensive, according to how the property changes when the size (or extent) of the system changes. According to IUPAC, an intensive quantity is on ...

of interest by

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...

. For example,

specific leaf area Specific leaf area (SLA) is the ratio of leaf area to leaf dry mass. The inverse of SLA is Leaf Mass per Area (LMA). Rationale Specific leaf area is a ratio indicating how much leaf area a plant builds with a given amount of leaf biomass: SLA \ = ...

leaf A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...

area divided by leaf mass. A ''named specific quantity'' is a generalization of the concept, in which the divisor quantity is not mass, the name of which is usually placed before "specific" in the term (e.g.,

thrust-specific fuel consumption Thrust-specific fuel consumption (TSFC) is the fuel efficiency of an engine design with respect to thrust output. TSFC may also be thought of as fuel consumption (grams/second) per unit of thrust (newtons, or N), hence ''thrust-specific''. This fi ...

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

Mass-specific quantities

Per unit of mass (short form of ''mass-specific''): *

Specific absorption rate Specific absorption rate (SAR) is a measure of the rate at which energy is absorbed per unit mass by a human body when exposed to a radio frequency (RF) electromagnetic field. It can also refer to absorption of other forms of energy by tissue, inc ...

, power absorbed per unit mass of tissue at a given frequency *

Specific activity Specific activity is the activity per unit mass of a radionuclide and is a physical property of that radionuclide. Activity is a quantity (for which the SI unit is the becquerel) related to radioactivity, and is defined as the number of radi ...

, radioactivity in becquerels per unit mass *

Specific energy Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, sto ...

, defined as energy per unit mass * Specific enzyme activity, activity per milligram of total protein **

Specific internal energy The internal energy of a thermodynamic system is the total energy contained within it. It is the energy necessary to create or prepare the system in its given internal state, and includes the contributions of potential energy and internal kinet ...

internal energy The internal energy of a thermodynamic system is the total energy contained within it. It is the energy necessary to create or prepare the system in its given internal state, and includes the contributions of potential energy and internal kinet ...

per unit mass **

Specific kinetic energy Specific kinetic energy is kinetic energy of an object per unit of mass. It is defined as \begin e_k = \frac \end v^2 . Where e_k is the specific kinetic energy and v is velocity. It has units of J/kg, which is equivalent to m2/s2. Energy ( ...

, kinetic energy of an object per unit of mass *

Specific enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant p ...

, enthalpy per unit mass *

Specific force Specific force is defined as the non-gravitational force per unit mass. :\mbox = \frac Specific force (also called g-force and mass-specific force) is measured in meters/second² (m·s−2) which is the units for acceleration. Thus, specific for ...

, defined as the non-gravitational force per unit mass *

Specific growth rate Relative growth rate (RGR) is growth rate relative to size - that is, a rate of growth per unit time, as a proportion of its size at that moment in time. It is also called the exponential growth Exponential growth is a process that increases qua ...

, increase in cell mass per unit cell mass per unit time *

Specific heat capacity In thermodynamics, the specific heat capacity (symbol ) of a substance is the heat capacity of a sample of the substance divided by the mass of the sample, also sometimes referred to as massic heat capacity. Informally, it is the amount of heat t ...

, 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 (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition. Latent heat can be understo ...

, latent heat per unit mass *

Specific leaf area Specific leaf area (SLA) is the ratio of leaf area to leaf dry mass. The inverse of SLA is Leaf Mass per Area (LMA). Rationale Specific leaf area is a ratio indicating how much leaf area a plant builds with a given amount of leaf biomass: SLA \ = ...

, leaf area per unit dry leaf mass *

Specific modulus Specific modulus is a materials property consisting of the elastic modulus per mass density of a material. It is also known as the stiffness to weight ratio or specific stiffness. High specific modulus materials find wide application in aerospace a ...

, a materials property consisting of the elastic modulus per mass density of a material *

Specific orbital energy In the gravitational two-body problem, the specific orbital energy \varepsilon (or vis-viva energy) of two orbiting bodies is the constant sum of their mutual potential energy (\varepsilon_p) and their total kinetic energy (\varepsilon_k), divided ...

, orbital energy per unit mass *

Specific power Power-to-weight ratio (PWR, also called specific power, or power-to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measuremen ...

, per unit of mass (or volume or area) *

Specific relative angular momentum In celestial mechanics, the specific relative angular momentum (often denoted \vec or \mathbf) of a body is the angular momentum of that body divided by its mass. In the case of two orbiting bodies it is the vector product of their relative positi ...

, of two orbiting bodies is angular momentum per unit reduced mass, or the vector product of the relative position and the relative velocity *

Specific surface area Specific surface area (SSA) is a property of solids defined as the total surface area of a material per unit of mass, (with units of m2/kg or m2/g) or solid or bulk volume (units of m2/m3 or m−1). It is a physical value that can be used to det ...

, per unit of mass, volume, or cross-sectional area *

Specific volume In thermodynamics, the specific volume of a substance (symbol: , nu) is an intrinsic property of the substance, defined as the ratio of the substance's volume () to its mass (). It is the reciprocal of density (rho) and it is related to the m ...

, volume per unit mass, i.e. the reciprocal of density

Other specific quantities

Per unit of other type. The dividing unit is sometimes added before the term "specific", and sometimes omitted. *

Brake specific fuel consumption Brake-specific fuel consumption (BSFC) is a measure of the fuel efficiency of any prime mover that burns fuel and produces rotational, or shaft power. It is typically used for comparing the efficiency of internal combustion engines with a shaft out ...

, fuel consumption per unit of braking power *

Thrust specific fuel consumption Thrust-specific fuel consumption (TSFC) is the fuel efficiency of an engine design with respect to thrust output. TSFC may also be thought of as fuel consumption (grams/second) per unit of thrust (newtons, or N), hence ''thrust-specific''. This fi ...

, fuel consumption per unit of thrust *

Specific acid catalysis In acid catalysis and base catalysis, a chemical reaction is catalyzed by an acid or a base. By Brønsted–Lowry acid–base theory, the acid is the proton (hydrogen ion, H+) donor and the base is the proton acceptor. Typical reactions catalyze ...

, in which the reaction rate is proportional to the concentration of the protonated solvent molecules *

Specific acoustic impedance Acoustic impedance and specific acoustic impedance are measures of the opposition that a system presents to the acoustic flow resulting from an acoustic pressure applied to the system. The SI unit of acoustic impedance is the pascal-second per cub ...

, ratio of sound pressure p to particle velocity v at a single frequency * Specific capacity of a water well, quantity of water produced per (length) unit of drawdown * Specific conductance, conductance per meter. Identical to

electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allow ...

Specific detectivity Specific detectivity, or ''D*'', for a photodetector is a figure of merit used to characterize performance, equal to the reciprocal of noise-equivalent power (NEP), normalized per square root of the sensor's area and frequency bandwidth (reciproca ...

of a photodetector *

Specific fuel consumption (disambiguation) Specific fuel consumption may refer to: * Brake-specific fuel consumption, fuel efficiency within a shaft engine * Thrust-specific fuel consumption Thrust-specific fuel consumption (TSFC) is the fuel efficiency of an engine design with respect to ...

. Fuel consumption per unit thrust, or per unit power. Type defined as above. *

Specific gas constant The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment per ...

, per molar mass *

Specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...

relative density Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

with respect to water (density per water density) * Specific heat of vaporization,

enthalpy of vaporization The enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. T ...

, vaporizing heat per mole *

Specific humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...

, mass of water vapor per unit mass dry air *

Specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse i ...

, impulse (momentum change) per unit of propellant (either per unit of propellant mass, or per unit of propellant by Earth-weight) * Specific mass, actually meaning ''volume-specific'' mass, or mass per unit volume. Same as

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

* Specific melting heat,

enthalpy of fusion In thermodynamics, the enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a s ...

; melting heat per mole *

, elastic modulus per mass density * Specific properties of a substance * Specific resistance (disambiguation), several scientific meanings * Specific rotation of a chemical, angle of optical rotation α of plane-polarized light per standard sample with a path length of one decimeter and a sample concentration of one gram per millilitre *

Specific speed Specific speed ''N's'', is used to characterize turbomachinery speed. Common commercial and industrial practices use dimensioned versions which are of equal utility. Specific speed is most commonly used in pump applications to define the su ...

, unitless figure of merit 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 In the field of hydrogeology, ''storage properties'' are physical properties that characterize the capacity of an aquifer to release groundwater. These properties are storativity (S), specific storage (Ss) and specific yield (Sy). According to '' ...

specific yield In the field of hydrogeology, ''storage properties'' are physical properties that characterize the capacity of an aquifer to release groundwater. These properties are storativity (S), specific storage (Ss) and specific yield (Sy). According to '' ...

, and specific capacity, characterize the capacity of an aquifer to release groundwater from storage per unit decline in hydraulic head pressure *

Specific strength The specific strength is a material's (or muscle's) strength (force per unit area at failure) divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio or strength-to-mass ratio. In fiber or textile applic ...

, material strength (pressure required at failure) per unit material density *

, per unit of mass, volume, or cross-sectional area * Specific surface energy, free energy per unit surface-area *

Specific thrust Specific thrust is the thrust per unit air mass flowrate of a jet engine (e.g. turbojet, turbofan, etc.) and can be calculated by the ratio of net thrust/total intake airflow. Low specific thrust engines tend to be more efficient of propellant (a ...

, thrust per unit air intake rate *

Specific weight The specific weight, also known as the unit weight, is the weight per unit volume of a material. A commonly used value is the specific weight of water on Earth at , which is .National Council of Examiners for Engineering and Surveying (2005). ''Fu ...

, weight per unit volume

References

{{reflist

Mass-specific quantities

Other specific quantities

References

See also