Tensile deformation occurs when two forces of equal in magnitude and opposite in direction act perpendicularly on the cross sections of opposite ends of a material such as a rod or a wire, as shown in Figure 6.8. A tensile force may stretch/elongate or compress a body. The quantity called stress, determines the amount of deformation.

The type of stress produced by tensile/normal forces is referred to as the normal stress, or tensile stress. Tensile stress is defined as the ratio of tensile force (F) to the cross – sectional area A of the wire.

The SI unit of stress is newton per square meter (N/m²).
The amount of deformation on a body can be measured by a quantity known as tensile strain of the body. Tensile strain is defined as the fractional change in length; i.e., the ratio of the extension L produced by the tensile stress to the original length (L₀) of the wire.

Tensile strain is just a pure number without a unit as it is a ratio of two lengths.