Hooke's Law was one of the many great achievements of Robert Hooke's life. This general law of mechanics states that stress is directly proportional to strain. Basically if one applies a force, F, to a spring, that spring will stretch a distance, x, away from the equilibrium position. The equation for Hooke's law is:

F = -kx

k is known as the spring constant. A spring with a large spring constant requires a larger force to stretch the spring the same distance as a spring with a small spring constant. In other words, a spring with a large spring constant is very hard to stretch and compress where as a spring with a small spring constant is very easy to stretch and compress. The only limitation on this law is if the spring is streched beyond its elastic limit, meaning that there is a limit to a spring where if you stretch it to much it will deform, thus the spring will have a new spring constant.

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