When a object is subjected to loads it develops resisting forces. To find the resisting forces developed a section plane may be passed through the member and equilibrium of any one part may be considered.
Each part is in equilibrium under the action of applied forces and internal resisting forces. The resisting forces may be conveniently split into normal and parallel to the section plane.
The resisting force parallel to the plane is called shearing resistance. The intensity of resisting force normal to the sectional plane is called intensity of Normal Stress.