The ratio of change in length to original length is : 

Concept:

Linear (Axial) Strain:

It is defined as the amount of deformation in the direction of the applied force divided by the initial length of the material.

\(Strain = {change\: in\: dimension \over\: original\: dimension}\)

There are three types of strain

1. Volumetric strain
2. Longitudinal strain
3. Shear strain

When we take the strain in longitudinal direction i.e. (change in length / original length) then it is called the longitudinal strain and when the  force making a change in length is compressive in nature the corresponding strain is called a compressive strain, similarly, when the force is tensile in nature, the corresponding strain will be a tensile strain

Important Points 

• When we take the strain in lateral direction i.e. (change in diameter / original diameter) then it is called lateral strain.
• Whenever there is stress applied on an object from all the sides or some sides then there will be a change in its volume (dV) and if its original volume is V then according to the definition of strain volumetric strain = δv/v.
• Shear strain is the ratio of the change in deformation to its original length perpendicular to the axes of the member due to shear stress.