Explanation: Stiffness (k): It is defined as the ability of the material to resist the deformation of an object. Stiffness is also defined as the ratio of load applied to the deflection. $k= \frac{P}{\delta}$ Deformation of axially loaded members: The deformation of a structural member with known geometry and subjected to an axial load can be determined by the equation of the form, $\delta = \frac{{PL}}{{AE}}$ $\therefore \delta = \frac{P}{{\frac{{AE}}{L}}}$ ${\frac{{AE}}{L}} = \frac{P}{{\delta}} =k$ The term $\frac{{AE}}{L}$ is defined as the stiffness of the bar.