Those of you familiar with Hooke’s law will be aware that the force a material exerts is proportional to the energy used to deform it.
In other words. The more you try and bend or deform a material, the harder it is to deform it further.
Hooke's law is a law of physics that states that the force (F) needed to extend or compress a spring by some distance (x) scales linearly with respect to that distance—that is, Fs = kx, where k is a constant factor characteristic of the spring (i.e., its stiffness), and x is small compared to the total possible deformation of the spring. The law is named after 17th-century British physicist Robert Hooke. He first stated the law in 1676 as a Latin anagram.
He published the solution of his anagram in 1678 as: ut tensio, sic vis ("as the extension, so the force" or "the extension is proportional to the force"). Hooke states in the 1678 work that he was aware of the law since 1660.
Constant force springs are best used as a counterbalance. In everyday application these springs are used most commonly to supply a retracting force for items such as self-closing doors, seatbelts and interior blinds.