Specific properties
Encyclopedia
Specific properties of a substance are derived from other intrinsic and extrinsic properties
(or intensive and extensive properties
) of that substance. For example, the density
of steel (a specific and intrinsic property) can be derived from measurements of the mass of a steel bar (an extrinsic property) divided by the volume of the bar (another extrinsic property). Similarly, the specific gravity
of a liquid is derived from the density of the liquid divided by the density
of water
(two intrinsic properties).
Uses of specific properties
Reference tables: Specific properties are often used in reference tables as a means of recording material data in a manner that is independent of size or mass. This allows the data to be broadly applied while keeping the table compact.
Ranking, Classifying, and Comparing: Specific properties are useful for making comparisons about one attribute while cancelling out the effect of variations in another attribute. For instance, steel alloys are typically stronger than aluminum alloys but are also much denser. Greater strength allows less metal to be used, which makes the choice between the two metals less than obvious. To simplify the comparison, one would compare the specific strength
(strength to weight ratio) of the two metals. A more everyday example is grocery shopping. The two kilogram package sells for a higher price than the one kilogram package, but what matters is the "specific price", commonly called the unit cost (cost per kilogram).
Mnemonics and Qualitative Reasoning: In many instances, specific properties are more intuitive or are easier to remember than the original properties in SI or English units. For instance, it is easier to conceptualize an acceleration of 2 g's than an acceleration of 19.6 meters per second squared. It is easy to remember that the specific gravity of water is 1.0 and that something with a higher specific gravity will sink in water.
Other examples of specific properties:
specific heat, specific modulus
, specific volume
, specific activity
, specific impulse
, specific power
, specific fuel consumption
Intrinsic and extrinsic properties
An intrinsic property is an essential or inherent property of a system or of a material itself or within. It is independent of how much of the material is present and is independent of the form the material, e.g., one large piece or a collection of smaller pieces...
(or intensive and extensive properties
Intensive and extensive properties
In the physical sciences, an intensive property , is a physical property of a system that does not depend on the system size or the amount of material in the system: it is scale invariant.By contrast, an extensive property In the physical sciences, an intensive property (also called a bulk...
) of that substance. For example, the density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of steel (a specific and intrinsic property) can be derived from measurements of the mass of a steel bar (an extrinsic property) divided by the volume of the bar (another extrinsic property). Similarly, the specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
of a liquid is derived from the density of the liquid divided by the density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
(two intrinsic properties).
Uses of specific properties
Reference tables: Specific properties are often used in reference tables as a means of recording material data in a manner that is independent of size or mass. This allows the data to be broadly applied while keeping the table compact.
Ranking, Classifying, and Comparing: Specific properties are useful for making comparisons about one attribute while cancelling out the effect of variations in another attribute. For instance, steel alloys are typically stronger than aluminum alloys but are also much denser. Greater strength allows less metal to be used, which makes the choice between the two metals less than obvious. To simplify the comparison, one would compare the specific strength
Specific strength
The specific strength is a material's strength divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. In fiber or textile applications, tenacity is the usual measure of specific strength...
(strength to weight ratio) of the two metals. A more everyday example is grocery shopping. The two kilogram package sells for a higher price than the one kilogram package, but what matters is the "specific price", commonly called the unit cost (cost per kilogram).
Mnemonics and Qualitative Reasoning: In many instances, specific properties are more intuitive or are easier to remember than the original properties in SI or English units. For instance, it is easier to conceptualize an acceleration of 2 g's than an acceleration of 19.6 meters per second squared. It is easy to remember that the specific gravity of water is 1.0 and that something with a higher specific gravity will sink in water.
Other examples of specific properties:
specific heat, specific modulus
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 applications where minimum structural weight is...
, specific volume
Specific volume
In thermodynamics, the specific volume of a substance is the ratio of the substance's volume to its mass. It is the reciprocal of density:In thermodynamics, the specific volume of a substance is the ratio of the substance's volume to its mass...
, specific activity
Specific activity
In nuclear sciences and technologies, "activity" is the SI quantity related to the phenomenon of natural and artificial radioactivity. The SI unit of "activity" is becquerel, Bq, while that of "specific activity" is Bq/kg. The old unit of "activity" was curie, Ci, while that of "specific activity"...
, specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
, specific power
Specific power
In physics and engineering, surface power density or sometimes simply specific power is power per unit area.-Applications:* The intensity of electromagnetic radiation can be expressed in W/m2...
, specific fuel consumption
Specific fuel consumption
Thrust specific fuel consumption or sometimes simply specific fuel consumption, SFC, is an engineering term that is used to describe the fuel efficiency of an engine design with respect to thrust output...