What's Hysteresis?

   Webster's Seventh New Collegiate Dictionary tells us:

   hys-ter-e-sis:
          n [NL, fr. Gk hysteresis shortcoming, fr. hysterein to be late, fall
          short, fr. hysteros later]

          a retardation of the effect when the forces acting upon a body are changed
          (as if from viscosity or internal friction); esp: a lagging in the values
          of resulting magnetization in a magnetic material (as iron) due to a
          changing magnetizing force. -hys-ter-et-ic adj

   There seems to be no [1]etymological link between hysteresis and either
   hysterical (fr. L hystericus of the womb) or history (fr. Gk, inquiry, history,
   fr. histor, istor knowing, learned). This is too bad, as there are scientific
   connections to both words. (There is no link, scientific or etymological, to
   histolysis, the breakdown of bodily tissues, or to blood.)

   Hysteresis represent the history dependence of physical systems. If you push on
   something, it will yield: when you release, does it spring back completely? If it
   doesn't, it is exhibiting hysteresis, in some broad sense. The term is most
   commonly applied, as Webster implies, to magnetic materials: as the external
   field with the signal from the microphone is turned off, the little magnetic
   domains in the tape don't return to their original configuration (by design,
   otherwise your record of the music would disappear!) Hysteresis happens in lots
   of other systems: if you place a large force on your fork while cutting a tough
   piece of meat, it doesn't always return to its original shape: the shape of the
   fork depends on its history.

   [fig1.gif]

   Hysteresis loops happen when you repeatedly wiggle the system back and forth
   (cycle the field up and down). The magnetization of a tape will ``lag behind'' as
   the field sweeps up and as it sweeps down. The memory in the tape is the
   magnetization remaining as the field is released to zero from a large value. In
   magnetic tapes, this lag is [2]repeatable: the shape of the loop after the first
   cycle is roughly the same as it is after many cycles. (This is convenient for
   doing multiple recordings on the same tape.) This is not true of many other
   systems: forks, for example, after being bent back and forth many times, will
   actually become stiffer (``work hardening'') and then break. There is a class of
   metals (called [3]shape memory alloys) that can be bent or stretched plastically
   large distances back and forth many times without work hardening: this
   superelastic behavior is only one property of these interesting materials.

   Many hysteretic systems make [4]screeching noises as they respond to their
   external load (hence, the natural connection with hysteria). [5]

References

   More information:
     * [6]Authors
     * [7]Hysteresis
     * [8]Noise in Hysteresis
     * [9]Return Point Memory
     * [10]The Critical Point
     * [11]The Epsilon Expansion
     ____________________________________________________________________________

                                        Links Back

   [12][smiley.gif] Entertaining Science done at
   [13][LASSP_Icon.gif] LASSP.
     ____________________________________________________________________________

   Last modified: June 30, 1994

   [14][sethna_icon.gif]


    Jim Sethna, sethna@lassp.cornell.edu

   [15][CoverFrontIcon.gif] Statistical Mechanics: Entropy, Order Parameters, and
   Complexity, now available at Oxford University Press ([16]USA, [17]Europe).

References

   1. https://sethna.lassp.cornell.edu/hysteresis/etymological_def.html
   2. https://sethna.lassp.cornell.edu/hysteresis/ReturnPointMemory.html
   3. https://sethna.lassp.cornell.edu/Tweed/What_Are_Martensites.html
   4. https://sethna.lassp.cornell.edu/hysteresis/noise.html
   5. https://sethna.lassp.cornell.edu/hysteresis/references.html
   6. https://sethna.lassp.cornell.edu/hysteresis/authors.html
   7. https://sethna.lassp.cornell.edu/hysteresis/hysteresis.html
   8. https://sethna.lassp.cornell.edu/hysteresis/noise.html
   9. https://sethna.lassp.cornell.edu/hysteresis/ReturnPointMemory.html
  10. https://sethna.lassp.cornell.edu/hysteresis/HysteresisCriticalPoint.html
  11. https://sethna.lassp.cornell.edu/hysteresis/EpsilonExpansion.html
  12. http://www.lassp.cornell.edu/LASSP_Science.html
  13. http://www.lassp.cornell.edu/
  14. https://sethna.lassp.cornell.edu/sethna.html
  15. https://sethna.lassp.cornell.edu/StatMech
  16. http://www.us.oup.com/us/catalog/general/subject/Physics/QuantumPhysics/?view=usa&ci=9780198566779
  17. http://www.oup.com/uk/catalogue/?ci=9780198566779