Simple stress
When we apply a force on a body, it undergoes some deformation. The molecules of the body resist this deformation. The resistance (to deformation) per unit area is called stress.
Mathematically
Stress (σ) = Force or Load (P) / Area (Area of cross section)
The S.I. unit of stress is Pascal (Pa).
There are mainly two types of stresses
Tensile stress – Two equal and opposite forces are applied on a body in order to increase its length. The cross section area of the body gets decreased.
Compressive stress – Two equal and opposite forces are applied on a body in order to shorten its length. The cross section area of the body gets increased.