Answer: 1. Strain
The deformation per unit length is called strain.
Strain: It is described as the proportion of a body's new dimension to its original dimension following deformation. Since the ratio is between two quantities of the same dimension, it is a dimensionless quantity.
Linear Strain: It is referred to as the ratio of the body's original length in the direction of the force to the change in length brought on by the deformation of any deformed body.
Lateral Strain: It is defined for any deformed body as the ratio of the body's original length in the direction perpendicular to the force to the change in length (breadth of a rectangular bar or diameter of a circular bar) as a result of the deformation.
Hence the deformation per unit length is called strain.