A substance is in equilibrium position in its original form due to the effect of interatomic forces. When external force is applied on any substance then as a result there is change in the shape or size or both of the substance and internal reactive force is produced in the substance. When external forces are removed then due to internal reactive forces the substance regains its original configuration. Internal reactive forces are also called restoring forces. Restoring forces are equal in magnitude to the external forces but opposite in direction. In equilibrium position; the internal reactive force or the restoring force per unit cross sectional area originated due to strain is called stress.
When deforming force is applied an any object then there is change in its length or volume or shape. The proportional change produced in the shape and size of an object due to the deforming force is called strain. It is a dimensionless quantity.
According to deformation strain have a three types.
(a) Longitudinal strain
(b) Volume strain
(c) Shearing strain
The ratio of longitudinal stress to longitudinal strain is called Young’s modulus of elasticity in elasticity limit. It is represented by Y.
Young’s modulus of elasticity
If on any wire of longitudinal cross sectional area A a tensile force F is applied then its initial length L and change in length is l, then;
The value of Y is calculated only for solids and it is a characteristic of solids.
