Lec.5/Materials physics
2nd class/polymer dep.
Physical properties of materials:
Introduction and classification:
A physical property is any property that is measurable whose value
describes a state of a physical system. The changes in the physical
properties of a system can be used to describe its transformations or
evolutions between its momentary states. Physical properties are often
referred to as observables. They are not modal properties.
Physical properties are often characterized as intensive and extensive
properties. An intensive property does not depend on the size or extent of
the system, nor on the amount of matter in the object, while an extensive
property shows an additive relationship. These classifications are in
general only valid in cases when smaller subdivisions of the sample do
not interact in some physical or chemical process when combined.
Properties may also be classified with respect to the directionality of their
nature. For example, isotropic properties do not change with the direction
of observation, and anisotropic properties do have spatial variance.
It may be difficult to determine whether a given property is a material
property or not. Color, for example, can be seen and measured; however,
what one perceives as color is really an interpretation of the reflective
properties of a surface and the light used to illuminate it. In this sense,
many ostensibly physical properties are called supervenient. A
supervenient property is one which is actual, but is secondary to some
underlying reality. This is similar to the way in which objects are
supervenient on atomic structure. A cup might have the physical
properties of mass, shape, color, temperature, etc., but these properties are
supervenient on the underlying atomic structure, which may in turn be
supervenient on an underlying quantum structure.
Physical properties are contrasted with chemical properties which
determine the way a material behaves in a chemical reaction.
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Lec.5/Materials physics
2nd class/polymer dep.
An intensive property is a bulk property, meaning that it is a physical
property of a system that does not depend on the system size or the
amount of material in the system. Examples of intensive properties
include temperature, refractive index, density, and hardness of an object.
When a diamond is cut, the pieces maintain their intrinsic hardness (until
their size reaches a few atoms thick).
By contrast, an extensive property is one that is additive for
independent, non-interacting subsystems. The property is proportional to
the amount of material in the system. For example, both the mass and the
volume of a diamond are directly proportional to the amount that is left
after cutting it from the raw mineral. Mass and volume are extensive
properties, but hardness is intensive.
Intensive properties
An intensive property is a physical quantity whose value does not depend
on the amount of the substance for which it is measured. For example, the
temperature of a system in thermal equilibrium is the same as the
temperature of any part of it. If the system is divided the temperature of
each subsystem is identical. The same applies to the density of a
homogeneous system; if the system is divided in half, the mass and the
volume change in the identical ratio and the density remains unchanged.
Additionally, the boiling point of a substance is another example of an
intensive property. For example, the boiling point for water is 100 °C at a
pressure of one atmosphere, a fact which remains true regardless of
quantity.
According to the state postulate, for a sufficiently simple thermodynamic
system, only two independent intensive variables are needed to fully
specify the entire state of a system. Other intensive properties can be
derived from the two known values.
Some intensive properties, such as viscosity, are empirical macroscopic
quantities and are not relevant to extremely small systems.
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Lec.5/Materials physics
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Combined intensive properties
There are four properties in any thermodynamic system, two are intensive
and two are extensive.
If the set of parameters, , are intensive properties {a i }and another set, ,
are extensive properties {Aj}, then the function is an intensive property if
for all
It follows, for example, that the ratio of two extensive properties is an
intensive property - density (intensive) is equal to mass (extensive)
divided by volume (extensive).
Examples
Examples of intensive properties include:
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chemical potential
concentration
density (or specific gravity)
ductility
elasticity
electrical resistivity
hardness
magnetic field
magnetization
malleability
melting point and boiling point
molar absorptivity
pressure
specific energy
specific heat capacity
specific volume
spectral absorption maxima (in solution)
temperature
viscosity
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Lec.5/Materials physics
2nd class/polymer dep.
Extensive properties
An extensive property is defined by the IUPAC Green Book as a physical
quantity which is the sum of the properties of separate non-interacting
subsystems that compose the entire system.[ The value of such an additive
property is proportional to the size of the system it describes, or to the
quantity of matter in the system. Taking on the example of melting ice,
the amount of heat required to melt ice is an extensive property. The
amount of heat required to melt one ice cube would be much less than the
amount of heat required to melt an iceberg, so it is dependent on the
quantity.
Extensive properties are the counterparts of intensive properties, which
are intrinsic to a particular subsystem. Dividing one type of extensive
property by a different type of extensive property will in general give an
intensive value. For example, mass (extensive) divided by volume
(extensive) gives density (intensive).
Combined extensive properties
If a set of parameters are {ai} intensive properties and another set are
extensive properties { Aj}, then the function is an extensive property if
for all α ,
Examples of extensive properties include
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energy
entropy
Gibbs energy
length
mass
particle number
momentum
number of moles
volume
magnetic moment
electrical charge
weight
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Lec.5/Materials physics
2nd class/polymer dep.
Although not true for all physical properties, some properties have
corresponding extensive and intensive analogs, many of which are
thermodynamic properties. Examples of such extensive thermodynamic
properties, that are dependent on the size of the thermodynamic system in
question, include volume, internal energy, enthalpy, entropy, Gibbs free
energy, Helmholtz free energy, and heat capacity (in the sense of thermal
mass). The symbols of these extensive thermodynamic properties shown
here are capital letters.
For homogeneous substances, these extensive thermodynamic properties
each have corresponding intensive thermodynamic properties, which are
expressed on a per mass or volume basis. The name is usually prefixed
with the adjective specific to indicate that they are bulk properties, valid
at any location (smaller subdivision) in a thermodynamic system. They
may be dependent on other conditions at any point, such as temperature,
pressure, and material composition, but are not considered dependent on
the size of a thermodynamic system or on the amount of material in the
system.
Specific volume is volume per mass, the reciprocal of density which
equals mass per volume.
Corresponding extensive and intensive thermodynamic properties
Extensive
Intensive
Symbol SI units
Symbol
SI units
property
property**
m3/kg or
3
Volume
V
m or L* Specific volume***
v
L*/kg
Internal energy
U
J
Specific internal energy
u
J/kg
Entropy
S
J/K
Specific entropy
s
J/(kg·K)
Enthalpy
H
J
Specific enthalpy
h
J/kg
Specific Gibbs free
Gibbs free energy
G
J
g
J/kg
energy
Heat capacity
Specific heat capacity
CV
J/K
cv
J/(kg·K)
at constant volume
at constant volume
Heat capacity
Specific heat capacity
at constant
CP
J/K
cP
J/(kg·K)
at constant pressure
pressure
* L = liter, J = joule
** specific properties, expressed on a per mass basis
*** Specific volume is the reciprocal of density.
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Lec.5/Materials physics
2nd class/polymer dep.
Common Physical Properties
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Absorption of electromagnetic - The way a photon’s energy is
taken up by matter
Absorption (physical) - Absorption between two forms of matter
Albedo - Reflecting power of a surface
Angular momentum - The amount of rotation of an object
Area - Amount of a two dimensional surface in a plane
Brittleness - Tendency of a material to break under stress
Boiling point - Temperature where a liquid forms vapor
Capacitance - Ability of an object to store an electrical charge
Color - Hue of an object as perceived by humans
Concentration - Amount of one substance in a mixture
Density - Mass per unit volume of a substance
Dielectric constant - Storage and dissipation of electric and
magnetic energy
Ductility - Ability of a substance to be stretched into a wire
Distribution - Number of particles per unit volume in singleparticle phase space
Efficacy - Capacity to produce an effect
Elasticity - Tendency of a material to return to its former shape
Electric charge - Positive or negative electric charge of matter
Electrical conductivity - A material's ability to conduct electricity
Electrical impedance - Ratio of voltage to AC
Electrical resistivity - How strongly a flow of electric current is
opposed
Electric field - Made by electrically charged particles and timevarying magnetic fields.
Electric potential - Potential energy of a charged particle divided
by the charge
Emission - Spectrum of frequencies of electromagnetic radiation
emitted
Flexibility - Pliability
Flow rate - Amount of fluid which passes through a surface per
unit time.
Fluidity - Flows easily
Freezing point - Temperature where a liquid solidifies
Frequency - Number of repetitions in a given time frame
Hardness - How resistant solid matter is to external force
Inductance - When the current changes, the conductor creates
voltage
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Lec.5/Materials physics
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2nd class/polymer dep.
Intrinsic impedance - Ratio of electric and magnetic fields in an
electromagnetic wave
Intensity - Power transferred per unit area
Irradiance - Power of electromagnetic radiation per unit area
Length - Longest dimension of an object
Location - Place where something exists
Luminance - Amount of light that passes through a given area
Luminescence - Emission of light not resulting from heat
Luster - The way light interacts with the surface of a crystal,
mineral or rock
Malleability - Ability to form a thin sheet by hammering or rolling
a material
Magnetic moment - Force that the magnet exerts on electric
currents and the torque that a magnetic field exerts on it
Mass - An object's resistance to being accelerated
Melting point - Temperature where a solid changes to a liquid
Momentum - Product of the mass and velocity of an object
Permeability - Ability of a material to support a magnetic field
Smell - Scent or odor of a substance
Solubility - Ability of a substance to dissolve
Specific heat - Heat capacity per unit mass of a material
Temperature - Numerical measure of heat and cold
Thermal conductivity - Property of a material to conduct heat
Velocity - Rate of change in the position of an object
Viscosity - Resistance to deformation by stress
Volume - Space that a substance occupies
Now you have seen many different examples of physical
properties. Remember, what all they have in common is that they can be
measured.
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