Robert Hooke study about the effect of tensile force in 1676. Then, he stated that the law is defined the elastic of an object body. He gets that the length of a stretched an object body is proportional to the Force, F.

F=kx

Where x is the length increase (m), and k is a proportionality constant or spring constant:

Reference

1. https://en.wikipedia.org/wiki/Hooke%27s_law