When a body is given external deforming force it undergoes deformation. As the deforming force increases the restoring force also increases. The restoring force per unit area is called stress. Since, restoring force is equal to deforming force, stress can also be defined as the applied deforming force per unit area i.e.
Stress = Force/Area
Its unit is Nm-2or dyne cm-2.
Types of stress:
1. Normal stress:
If the applied deforming force is normal to the surface then the force per unit area is called normal stress.
a. Tensile stress
If on applying normal stress to the body the body undergoes elongation i.e. length of the body increases then the stress set up in the body is called tensile stress.
b. Compression stress
If on applying normal stress the body undergoes decrease in the length then the stress set up in the body is called compression stress.
2. Tangentially stress/ Shearing stress
If two equal and opposite forces are applied tangentially on two faces of the body and if one of the faces displaces through some distance from its original position then the body is said to be under tangentially stress or shearing stress.
3. Bulk stress/Volume stress/Hydraulic stress
When an object is immersed in fluid (liquid/gas) the body will experience force from all side as a result of which the volume of the body will decrease and the body is said to be in a stress called bulk stress.