What is meant by physical property?

The property of a material describes its characteristics. The properties of a material can be mechanical, physical, and chemical. These properties can be influenced by external parameters such as temperature, pressure, heat, or any external forces present in the system.

The measurable and observable properties of a system are termed the physical property. These properties are associated with the physical change of the system. Some of the physical properties are density, volume, melting point, freezing point, thermal conductivity, and so on. The physical properties of a system should not be confused with the mechanical properties of a system.

The mechanical properties of a system are the ones that are exhibited due to internal mechanisms, activated on the application of an external force. On the other hand, the chemical properties are associated with the chemical composition of the system; these properties are noticeable when the system undergoes a chemical change. Some of the chemical properties of the system are toxicity, acidity, and reactivity.

Knowledge of the physical properties of the system is essential for the design phase and various applications. Mary Anne White and Prof. Moskovits published their findings to understand the differences between the physical properties, mechanical properties, and chemical properties of a material.

Intensive and Extensive properties

The physical property of a material is generally classified into two categories; namely, intensive and extensive properties.

• Intensive property: It is the bulk property of a system. Intensive properties do not change with the system mass. In other words, these are the physical properties that do not depend on the extent or size of the system such as density, specific gravity, specific heat capacity, temperature, colour, magnetic property, electrical properties, brittleness, etc.
• Extensive property: These are the physical properties of the system that depend on the extent or the size of the system or amount of matter it is composed of, such as, entropy, enthalpy, Gibbs free energy, elasticity, malleability, ductility, permeability, hardness, resistivity and so on.

Physical properties of engineering materials

An engineering material is a material used in engineering applications. These materials are subjected to practical functionality and are made to withstand high external loads, deformations, and deflections. Some of the physical properties of engineering materials are:

Thermal conductivity

An increase in the temperature of a substance leads to an increase in the heat quantity of the substance. Thermal conductivity is the property of a material to conduct that heat. It refers to the ability of material with ease of heat transfer by conduction through the material. It arises from the atomic property of the material, availability of free electrons forms a major criterion for the thermal conductivity of a material. Thermal conductivity is majorly defined in Fourier's law of heat conduction. According to the law, the amount of heat transfer by conduction is proportional to the area and the thermal gradient. Mathematically, $Q=-KA\frac{dT}{dx}$, whereas the derivative $\frac{dT}{dx}$ is the thermal gradient, and $A$ is the area perpendicular to the heat flow.

Corrosion resistance

When a material is subjected to adverse environmental conditions, the chemical reaction that occurs produces a damaging chemical change and leads to the formations of products that tend to corrode the base material. The resistance offered by the material as a response to corrosion is termed the corrosion resistance of the material. The study of this property is of primary importance while designing civil engineering structures. Corrosion is a process of oxidation of the material that leads to a chemical change in the material. 

Tensile strength

Members such as bars, which are under the influence of axial loads or tensile forces, tend to deform along the axis of the application of the loads. The resistance of the material to resist such deformation is known as tensile strength. Many engineering applications such as designing engineering structures require the knowledge of the tensile strength of a material. The tensile strength of a material can be determined through a tensile test conducted on a universal testing machine (UTM). 

Density and specific gravity

Density is the physical property of a material that denotes the amount of mass that a substance possess. The density of a substance always remains constant until there is a rise or fall in the temperature of the substance. The amount of mass present in a unit volume of a substance is known as density. Mathematically, it is expressed as, $\rho =\frac{m}{v}$ where, $\rho$ is the density of the substance, $m$ is the mass of the substance and $v$ is the volume of the substance. The SI unit of density is $\frac{Kg}{m^3}$.

The specific gravity or relative density is determined by evaluating the ratio between the density of the given material and the density of water at normal temperature and pressure (NTP).

Mathematically, it is expressed as:

$\mathfrak{R}=\frac{{\rho }_{Subs\tan ce}}{{\rho }_{water}}$, where $\mathfrak{R}$ denotes relative density.

Context and Applications

The following topic finds its importance in the areas of engineering design and applications.

• Bachelors in Science in Physics
• Masters in Science in Physics
• Bachelors in Technology (Civil and Architect)

Practice Problems

1. Which of the following is the unit of density?

1. $\frac{\mathrm{Kg}}{m^3}$
2. $\frac{\mathrm{Kg}}{m}$
3. $\frac{\mathrm{Kg}}{m^2}$
4. None of these

Correct option- a

Explanation: The SI unit of density is expressed as $\frac{\mathrm{Kg}}{m^3}$.

2. Which of the following is an intensive property of the system?

1. Entropy
2. Enthalpy
3. Density
4. All of these

Correct option- c

Explanation: Intensive properties are independent of the mass of the system. For example, the density of a material does not depend on the mass of the system.

3. Extensive properties are those properties that are dependent on the amount of matter of the system. True or False?

Correct answer: True

Explanation: Extensive properties are those properties that depend on the extent or size of the system, that is, mass.

4. Which of the following expressions correctly signifies Fourier's law of heat conduction?

1. $Q=KA\frac{dT}{dx}$
2. $Q=-\mathrm{hA}∆T$
3. $Q=-\mathrm{KA}∆T$
4. $Q=-\mathrm{KA}\frac{dT}{dx}$

Correct option- d

Explanation: Fourier's law of heat conduction relates the area of the body with its thermal gradient, with the constant of proportionality, $K$, known as the coefficient of thermal conduction. Hence, the correct expression is $Q=-\mathrm{KA}\frac{dT}{dx}$.

5. Which of the following is a chemical property of a substance?

1. Toxicity
2. Reactivity
3. Acidity
4. All of these

Correct option- d

Explanation: Toxicity, reactivity, and acidity, all are the chemical properties associated with a substance. They are not associated with the physical change of the system but are associated with the chemical change of the system.

Related topics

• Magnetocaloric materials