two types, tensile stress and compressive stress. Tensile stress Internal forces on the two sides of ∆ A may pull each other, i.e., it is stretched by equal and opposite forces. Then, the longitudinal stress is called tensile stress. Figure .
Tensile stress Tensile stress F F F F Compressive stress When forces acting on the two sides of ∆ A push each other, ∆A is pushed by equal and opposite forces at the two ends. In this case, ∆ A is said to be under compression. Then, the longitudinal stress is called compressive stress. Figure .
Compressive stress Compressive stress F F F F our naked eyes but it exists in the material itself. When a body is subjected to such a deforming force, internal force is developed in it, called as restoring force. The force per unit area is called as stress. Stress, σ = Force Area = F A ( .
) The SI unit of stress is N m – or pascal (Pa) and its dimension is [ML – T – ]. Stress is a tensor. (i) Longitudinal stress and shearing stress: Let us consider a body as shown in Figure . .
When many forces act on the system (body), the center of mass (defined in unit ) remains at rest. However, the body gets deformed due to these forces and so the internal forces appear. Let ∆A be the cross sectional area of the body. The parts of the body on two sides of ∆A exert internal forces F and − F on each other which is due to deformation.
The force can be resolved in two components; F n normal to the surface ∆A (perpendicular to the surface) and F t tangential to the surface ∆A (tangent to the surface). The normal stress or longitudinal stress (σ n ) over the area is defined as σ n n F = ∆ Figure . Longitudinal stress Longitudinal stress F F F t F F n ∆ A - - - - Unit Properties of matter (i) Tensile strain: