What is strain? Explain longitudinal strain $(\varepsilon)$.

(N/A) When a solid body is subjected to an external deforming force,its dimensions change in three ways:
$(1)$ In length,$(2)$ In volume,and $(3)$ In shape.
The ratio of the change in dimension to the original dimension of a body is known as strain.
Longitudinal Strain: The deforming force that produces a fractional change in the length of a body is known as longitudinal strain.
If $L$ is the original length of the body and $F$ is the deforming force causing a change in length $\Delta L$,then the longitudinal strain $\varepsilon_{l}$ is given by:
$\varepsilon_{l} = \frac{\Delta L}{L}$
If the length increases,the corresponding longitudinal strain is called tensile strain,and if the length decreases,the corresponding strain is called compressive strain.