The internal restoring force acting per unit area of cross–section of the deformed body is called stress.
Stress = (Internal Restoring force/Area of cross section) = Finternal/A = Fexternal/A
SI Unit : Nm–2
Dimensions : [M1 L–1 T–2]
There are three types of stress :-
(a) Longitudinal Stress
(b) Volume Stress and
(c) Tangential Stress or Shear Stress
Let us discuss these one by one…..
(a) Longitudinal Stress :-
When the stress is normal to the surface of body, then it is known as longitudinal stress.
When the deforming force is along the length of an object then the stress developed is called longitudinal stress.
There are two types of longitudinal stress:-
(i) Tensile Stress : The longitudinal stress, produced due to increase in length of a body, is defined as tensile stress.
(ii) Compressive stress : The longitudinal stress, produced due to decrease in length of a body, is defined as compressive stress.
(b) Volume Stress:-If equal normal forces are applied on every point of the surface of a body, then it undergoes change in volume. The force opposing this change in volume per unit area is defined as volume stress.
(c) Tangential Stress or Shear Stress:-
When the external applied force is tangential or parallel to the surface of a body then the stress produced is known as shear stress. Due to this stress, the shape of the body changes or it gets twisted.