(Derived from the Greek word meaning “to lag behind.”) A retardation of the effect, as if from viscosity, when the forces acting upon the body are changing. A common illustration is the retentivity of induction in ferromagnetic materials such as iron and its alloys when the magnetizing force is changed. When such a substance is placed in a magnetizing coil and the magnetizing field is gradually increased to a given value, and then decreased, the magnetic induction, in decreasing does not follow the same relation to the magnetizing field that it did when the field was increasing, but lags behind the decreasing field. Hysteresis is analogous to mechanical inertia and the energy lost is analogous to that lost in mechanical friction. It presents a major problem in the design of electrical machines with iron cores such as transformers and rotating armatures. In instruments designed for very high frequencies, the retardation and losses are so great as to render iron cores useless. The stress-strain curves of vulcanized rubber also display hysteresis, in that strain (elongation, crystallization) persists when the deforming stress is removed, thus producing a hysteresis loop instead of a reversible pathway of the curves. This loop indicates a loss of resilient energy (Norman E. Gilbert).Note: The simple diagram shown below is a generalized representation of a hysteresis loop.
