Find a spring's stiffness with Hooke's law F = k x — enter the force and the extension to get the spring constant k, or solve for force or displacement.
Hooke's law says the force a spring exerts is proportional to how far it is stretched or compressed: F = k x. The spring constant k measures stiffness — a higher k means a stiffer spring that needs more force for the same extension.
Enter any two of force, extension and k to find the third. The law holds within the spring's elastic limit; beyond that the spring deforms permanently and the relationship breaks down. The energy stored is ½kx².
Divide the applied force by the resulting extension: k = F / x. If 20 N stretches a spring 0.1 m, k = 200 N/m.
Newtons per metre (N/m) — the force needed per metre of extension. A stiffer spring has a larger value.
Hooke's law states that the restoring force of a spring is proportional to its displacement: F = kx, valid within the elastic limit.
The elastic potential energy is ½kx² — half the spring constant times the extension squared.