Definition of Stress :
When a deforming force is applied on a body then the restoring forces are developed inside the body.
The restoring force is equal and opposite to the deforming force or applied force.
"The restoring force or deforming force per unit area of the body is called Stress".
Stress = External applied force or deforming force / Area of the body
Stress = F/A
In S.I, the unit of stress is N/m2 or Mm-2
The unit of Stress is also a Pascal (Pa)
1 Pa = 1 N/m2
Stress is Scalar quantity.
Dimensional Formula of stress = [MLT]
Type of Stress :
1. Normal Stress / Longitudinal Stress :
It is defined as the restoring force per unit area perpendicular to the surface of the body.
Normal Stress is of two types :
(I) Tensile stress (II) Compressive Stress
(I) Tensile Stress :
When two equal and opposite force are applied on a rod to increase it's length, a restoring force equal to the applied force F normal to the cross sectional area of the rod comes into existence.
Tensile Stress = F/A
"The restoring force or deforming force acting per unit area perpendicular to the cross-section of the body." is called Tensile stress.
(II) Compressive Stress :
When two equal and opposite force are applied on a rod to decrease it's length, a restoring force equal to the applied force F normal to the cross sectional area of the rod comes into existence.
"The restoring force or deforming force acting per unit area perpendicular to the cross-section of the body is called Compressive stress".
Compressive Stress = F/A
Under Tensile stress or compressive stress , the net force acting on an object is zero but the object is deformed.
2. Tangential stress / Shearing Stress :
When two equal and opposite forces act along the tangents to the surfaces of the opposite faces of an object, then one face of the object is displaced with respect to the other face.
"Tangential stress or Shearing stress is defined as the ratio of the force acting along the tangent to the surface to the area of the surface."
Shearing stress = F/A
3. Bulk Stress or Volume Stress or Hydraulic Stress :
When an object is immersed in a fluid ( liquid or gas ) , the fluid exerts force on the surfaces of the object as result of this , the volume of the object decrease.
"Bulk Stress is defined as the force acting perpendicular to the surface of the object per unit area of the object"
Bulk Stress = Force / Area
The effect of Stress is to Produce distortion or a change in size , volume and shape