In general there are two types of forces act on a body. They are
- Internal forces
- External forces
- Internal forces are the forces which are set up in the body due to externally applied force.
- The internal force set up in the body per unit area is known as stress.
- The external forces acting on the body are due to pressure exerted by one body on the other body or due to hydraulic pressure or atmospheric pressure.
- The amount of force due to pressure exerted by one body over other body or due to hydraulic pressure or atmospheric pressure per unit area is known as applied stress.
- The SI Unit of stress is N/m2
- Stress is a scalar quantity.
The plane on which shear stress is zero is called as principal plane and the normal stress acting on the principal plane is known as principal stress.