# Physical Properties of Materials

To finalize the material for an engineering product or application, we should have the knowledge of

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Water MeterAir MeterDigital PotentiometersBasic Construction of Wind TurbineCharacteristics of Sensors**physical properties of materials**. The physical properties of a material are those which can be observed without change of the identity of material. Some of these typical properties of a material are listed below-- Density
- Specific gravity
- State Change temperatures
- Coefficients of thermal expansion
- Specific Heat
- Latent heat
- Fluidity
- Weld ability
- Elasticity
- Plasticity
- Porosity
- Thermal conductivity
- Electrical Conductivity

## Density of Materials

**Density of a material**or substance is defined as “the mass per unit volume”. It is represented as the ratio of mass with volume of a material. It is denoted by “ρ”. Its unit in SI system is Kg/m^{3}. If, m is the mass of material in Kg, V is the volume of materiel in meter^{3}. Then the Density of material,## Specific Gravity of Materials

It is defined as the ratio of density of material with respect to density of a reference material or substance. It does not have any unite. Sometimes it is also called as relative density. For gravity calculation generally water is considered as a reference substance.## State Change Temperatures

Generally a substance is having three states called – solid state, liquid state, gaseous state. State change temperature is the temperature at which the substance changes from one state to another state. State change temperature are of following types- Melting point - It is the temperature (in °C or K) at which the substance changes from solid state to liquid state. Boiling point - It is the temperature (in °C or K) at which the substance changes from liquid state to gaseous state. Freezing point - It is the temperature (in °C or K) at which a liquid changes from liquid to solid state. Theoretically it is equal to the melting point. However, practically there may observed some difference.## Coefficient of Thermal Expansion

When a material is heated, it expends, due to which its dimensions change. Coefficient of thermal expansion, represents the expansion in material with increase of temperature. Thermal expansion coefficients are three types Coefficient of Linear Thermal Expansion The change in length of an object due change in temperature is related by “Coefficient of linear thermal expansion”. It denoted by “α_{L}” Where, ‘l’ is the initial length of object, ‘Δl’ is the change in length, ‘Δt’ is the change in the temperature. Unit of α_{L}is per °C. Coefficient of Area Thermal Expansion The change in area of an object due change in temperature is related by “Coefficient of Area thermal expansion”. It denoted by “αA” Where, ‘l’ is the initial length of object, ‘ΔA’ is the change in length, ‘Δt’ is the change in the temperature. Unit of α_{A}is per °C Coefficient of Volume Thermal Expansion The change in volume of an object due change in temperature is related by “Coefficient of volume thermal expansion”. It denoted by “α_{V}” Where, ‘l’ is the initial length of object, ‘ΔV’ is the change in length, ‘Δt’ is the change in the temperature. Unit of α_{A}is per °C