Hooke’s law is an approximation of the response of elastic (i.e., spring-like) bodies. It states: the extension of a spring is in direct proportion with the load applied to it. For instance, the spring is pulled downwards with either no-load, F_p, or twice F_p.

Many materials obey this law of elasticity as long as the load does not exceed the material’s elastic limit. Materials for which Hooke’s law is a useful approximation are known as linear-elastic or “Hookean” materials. Hookean materials are broadly defined and include springs as well as muscular layers of the heart. In simple terms, Hooke’s law says that stress is directly proportional to strain. Mathematically, Hooke’s law is stated as F=−kx   where:

1. x is the displacement of the spring’s end from its equilibrium position (a distance, in SI units: meters);
2. F is the restoring force exerted by the spring on that end (in SI units: N or kg m/s²); and
3. K is a constant called the rate or spring constant (in SI units: N/m or kg/s²). When this holds, the behavior is said to be linear. If shown on a graph, the line should show a direct variation.Multiple springs can act on the same point.