English: A force ${\displaystyle {\vec {F}}}$ is applied to a box of length ${\displaystyle L_{0}}$ on a flat side of area ${\displaystyle \Delta L}$. In the limit of small displacements we expect it to follow Hooke's law: ${\displaystyle F=k_{\text{string}}\Delta L}$. To find the spring constant, we examine the system at a smaller scale and seek the intrinsic variables: They are ${\displaystyle F/A}$ and ${\displaystyle \Delta L/l_{0}}$. Since the ratio of two intrinsic variables is also intrinsic, we conclude that Young's modulus ${\displaystyle Y}$ is also intrinsic, where ${\displaystyle F/A=Y(\Delta L/L)0)}$