### Hooke's law

Hooke's law named for the famous English scientist hook. hook investigate the relationship between stress and strain. He investigated and observed the amount of stretching of wires for different materials under loads. He notices a proportional elongation under proportional loads. then Hook developed the equation between axial stress and strain

σ=E*ε

where
σ= is the axial stress
ε=is the axial strain

The above equation expresses the linear relationship between stress and strain for a bar in simple tension or compression. this relationship is valid at the linearly elastic region for materials. it is known that the materials at the elastic region can recover the strain and the stress-strain curve at the elastic region exhibits a linear relationship for most of the materials. structural steel is an example of materials that exhibits a linear stress-strain relationship at the elastic region. usually, structures and machines designed at elastic regions to avoid permanent deformation. therefore this equation will be very helpful and used for structures and machines design