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## Stress

It is defined as the force applied on unit area to produce change in the shape,volume or length of a body.Mathematically it is expressed as:

The SI unit of stress (σ) is newton per square meter (Nm^{-2}),which is given the name pascal (pa).

Stress may cause a change in length,volume and shape.

### Tensile stress

When a stress changes the length,it is called tensile stress.

### Compressional stress

When a stress changes its volume, it is called compressional stress.

### Shear stress

When stress changes the shape, it is called shear stress.

## Strain

Strain is a measure of the deformation of a solid when stress is applied to it.In the case of deformation in one dimensional strain is defined as the frictional change in length.If Δl is the change in length and l is the original length,then strain is given by:

Since strain is ratio of lengths,it is dimensionless,and therefore,has no units.

### Tensile strain

If strain is ε is due to tensile stress σ,it is called tensile strain.

### Compressive strain:

If strain is produced as a result of compressive stress,it is called compressive strain.

### Volumetric strain

When the applied stress changes the volume,the change in volume per unit volume is known as volumetric strain.

### Shear strain

When the opposite faces of a rigid cube are subjected to shear stress.