# What is Stress? Stress Formula and Types

Stress is the force acting on the unit area of a material. Effect of stress on a body is named as strain. Stress can deform the body. How much force material experience can be measured using stress units. Stress can be categorised into three categories depending upon the direction of the deforming forces acting on the body.

### Stress Formula

The stress formula is the divided product of the force by the cross-section area σ = F/A

### Derivation of the Stress Formula

σ = refers to the amount of stress on the object

F = refers to the force that is acting on the object.
A = refers to the cross-sectional area

### Types of Stress

1. Normal Stress: As the name suggests, Stress is said to be Normal stress when the direction of the deforming force is perpendicular to the cross-sectional area of the body. The length of the wire or the volume of the body changes stress will be at normal. Normal stress can be further classified into two types based on the dimension of force.
• Longitudinal stress
• Bulk Stress or Volumetric stress

2. Longitudinal Stress: Consider a cylinder. When two cross-sectional areas of the cylinder are subjected to equal and opposite forces the stress experienced by the cylinder is called longitudinal stress.

Longitudinal Stress = Deforming Force / Area of cross section = F/A

As the name suggests, When the body is under longitudinal stress-

• The deforming force will be acting along the length of the body.
• Longitudinal stress results in the change in the length of the body, Hence thereby it affects slight change in diameter.

The Longitudinal Stress either stretch the object or compress the object along its length. Thus it can be further classified into two types based on the direction of deforming force-

• Tensile stress
• Compressive stress

3. Tensile Stress: If the deforming force or applied force results in the increase in the object’s length then the resulting stress is termed as tensile stress. For example: When a rod or wire is stretched by pulling it with equal and opposite forces(outwards) at both ends.

4. Compressive Stress: If the deforming force or applied force results in the decrease in the object’s length then the resulting stress is termed as compressive stress. For example: When a rod or wire is compressed/squeezed by pushing it with equal and opposite forces(inwards) at both ends.

5. Volume Stress: When the deforming force or applied force acts from all dimension resulting in the change of volume of the object then such stress in called volumetric stress or Bulk stress. In short, When the volume of body changes due to the deforming force it is termed as Volume stress.

6. Tangential Stress: When the direction of the deforming force or external force is parallel to the cross-sectional area, the stress experienced by the object is called shearing stress or tangential stress. This results in the change in the shape of the body.