This tutorial uses Hookes law to solve a physics problem in order to calculate the spring constant spring stiffnessIn physics the spring constant is how. Mathematically Hookes law is expressed as F kx where the applied force F equals a. Mechanical Engineering Calculators Mechanical Engineering Physics Lessons Physics And Mathematics F kx. . A spring constant is expressed in Newtons per millimeter of compression or Newtons per º. F k δ x. Its used to determine stability or instability. The formula for Hookes law specifically relates the change in extension of the spring x to the restoring force F generated in it. The spring is not stretched beyond the limit of proportionality and it stretches by 15 cm. The spring constant of this spring is 30000 Nm. The formula for finding the spring constant K is. The value of this constant depends on the qualities of the specific spring and this can be directly derived fr