4 ms·

People complaining that the hysteresis used in the article is different from the one they learned in school are incorrect. To begin with, in its introduction t

• adrian_b 4y ago
  You are right that according to the original definition of the word by J. A. Ewing ("When there are two qualities M and N such that cyclic variations of N cause cyclic variations of M, then if the changes of M lag behind those of N, we may say that there is hysteresis in the relation of M to N", Phil. Trans., 1885, 176, p. 524), the "rate dependent hysteresis" is a kind of hysteresis. Nevertheless, this kind of hysteresis is not interesting, it is just the phase difference between an output and an input of a linear network, a.k.a. the phase of the transfer function between that input and that output. This kind of hysteresis, i.e. such a phase difference between 2 variations, is ubiquitous, it appears in any system described by linear differential equations and also in any system described by non-linear differential equations when only small variations are applied to it. So there is no advantage in calling it hysteresis instead of using alternative terms, which had been used much earlier than "hysteresis", e.g. "phase difference" or "phase lag" or just "lag". The interesting forms of hysteresis, for which a new word was useful, because they could not be described using the older theories of linear systems, are those encountered in non-linear systems, e.g. ferromagnetic materials, ferroelectric materials, bistable electrical circuits, bistable mechanical switches, and so on. In all kinds of hysteresis, an output is a function not only of inputs but also of an internal state (which is determined by the past inputs of the system). However, in the case of the periodic steady-state analysis of a linear system, the internal state of the system is not considered explicitly, because the trick of replacing a system of linear differential equations in real variables with a system of algebraic equations in complex variables takes into account the internal state implicitly (i.e. the energy stored e.g. in electrical devices like capacitors and inductors, or in mechanical devices like springs and flywheels). So in the analysis of a linear system, the "rate-dependent hysteresis" does not need any special treatment. On the other hand, in the case of non-linear systems there is no trick allowing to ignore the hysteresis, it must be handled explicitly, using a state that depends non-linearly on the past inputs. In conclusion, it is true that the use of "hysteresis" in the parent article and in the Apple GUI is not incorrect from the point of view of the meaning of "hysteresis" in physics, but this is nonetheless a non-recommendable use of the word. Much less confusing and also shorter would be to say "Menu lag" or "Menu delay", instead of "Menu hysteresis".
  • balsam 4y ago
    Its a subtle point but I wanted to point out that all that nonlinearity, yes even in magnets, is due time lag. Apologies for not fleshing out the details but the “path-dependent internal state” is shorthand for saying that the magnet hasnt really reached thermal equilibrium at any point along the cycle. If you could wait for that to happen there would be no hysteresis. The internal state would then only depend on the temperature (and external fields etc) but not on “the history”. Of course, this kind of consistent physics isnt really relevant for engineering and so people have to add in easier to digest (but ultimately inconsistent and vacuous) ideas like path-dependence.