An object at rest is said to be in equilibrium. The subject concerned with the determination of the forces within a structure at rest is called statics. It is important when doing statics problems to apply the equilibrium conditions to only one object at a time. An object in static equilibrium is said to be in either: stable equilibrium, unstable equilibrium, neutral equilibrium. This depends on whether a slight displacement leads to: a return to the original position, further movement away from the original position, rest in the new position. An object in stable equilibrium is also said to be in balance. Hooke"s law applies to many elastic solids, and states that the change in length of an object is proportional to the applied force: If the force is too great, the object will exceed its elastic limit, which means it will no longer return to its original shape when the distorting force is removed.
