Editing Hysteresis (section)

==In mechanics==

===Elastic hysteresis===
[[Image:Elastic Hysteresis.svg|thumb|right|Elastic hysteresis of an idealized rubber band. The area in the centre of the hysteresis loop is the energy dissipated due to internal friction.]]
In the elastic hysteresis of rubber, the area in the centre of a hysteresis loop is the energy dissipated due to material [[internal friction]].

Elastic hysteresis was one of the first types of hysteresis to be examined.<ref name="LoveTreatise">{{cite book |author=Love, Augustus E. |title=Treatise on the Mathematical Theory of Elasticity (Dover Books on Physics & Chemistry) |publisher=Dover Publications |location=New York |year=1927 |isbn=978-0-486-60174-8}}</ref><ref name="Ewing">{{cite journal |first1=J. A. |last1= Ewing |author-link1=James Alfred Ewing |title=On hysteresis in the relation of strain to stress |journal=British Association Reports |year=1889 |pages=[https://archive.org/details/reportofbritisha90brit/page/502 502]|url=https://archive.org/details/reportofbritisha90brit}}</ref>

The effect can be demonstrated  using a [[rubber band]] with weights attached to it. If the top of a rubber band is hung on a hook and small weights are attached to the bottom of the band one at a time, it will stretch and get longer. As more weights are ''loaded'' onto it, the band will continue to stretch because the force the weights are exerting on the band is increasing. When each weight is taken off, or ''unloaded'', the band will contract as the force is reduced. As the weights are taken off, each weight that produced a specific length as it was loaded onto the band now contracts less, resulting in a slightly longer length as it is unloaded. This is because the band does not obey [[Hooke's law]] perfectly. The hysteresis loop of an idealized rubber band is shown in the figure.

In terms of force, the rubber band was harder to stretch when it was being loaded than when it was being unloaded. In terms of time, when the band is unloaded, the effect (the length) lagged behind the cause (the force of the weights) because the length has not yet reached the value it had for the same weight during the loading part of the cycle. In terms of energy, more energy was required during the loading than the unloading, the excess energy being dissipated as thermal energy.

Elastic hysteresis is more pronounced when the loading and unloading is done quickly than when it is done slowly.<ref>{{cite journal|first1=B. |last1=Hopkinson |first2=G. T. |last2=Williams |journal=[[Proceedings of the Royal Society]] |volume= 87 |year=1912 |pages=502 |doi=10.1098/rspa.1912.0104|title=The Elastic Hysteresis of Steel |bibcode = 1912RSPSA..87..502H|issue=598 |doi-access=free }}</ref> Some materials such as hard metals don't show elastic hysteresis under a moderate load, whereas other hard materials like granite and marble do. Materials such as rubber exhibit a high degree of elastic hysteresis.

When the intrinsic hysteresis of rubber is being measured, the material can be considered to behave like a gas. When a rubber band is stretched, it heats up, and if it is suddenly released, it cools down perceptibly. These effects correspond to a large hysteresis from the thermal exchange with the environment and a smaller hysteresis due to internal friction within the rubber. This proper, intrinsic hysteresis can be measured only if the rubber band is [[adiabatically|thermally]] isolated.

Small vehicle suspensions using [[rubber]] (or other [[elastomer]]s) can achieve the dual function of springing and damping because rubber, unlike metal springs, has pronounced hysteresis and does not return all the absorbed compression energy on the rebound. [[Mountain bike]]s have made use of elastomer suspension, as did the original [[Mini]] car.

The primary cause of [[rolling resistance]] when a body (such as a ball, tire, or wheel) rolls on a surface is hysteresis. This is attributed to the [[viscoelasticity|viscoelastic characteristics]] of the material of the rolling body.

===Contact angle hysteresis===
The [[contact angle]] formed between a liquid and solid phase will exhibit a range of contact angles that are possible. There are two common methods for measuring this range of contact angles. The first method is referred to as the tilting base method. Once a drop is dispensed on the surface with the surface level, the surface is then tilted from 0° to 90°. As the drop is tilted, the downhill side will be in a state of imminent wetting while the uphill side will be in a state of imminent dewetting. As the tilt increases the downhill contact angle will increase and represents the advancing contact angle while the uphill side will decrease; this is the receding contact angle. The values for these angles just prior to the drop releasing will typically represent the advancing and receding contact angles. The difference between these two angles is the contact angle hysteresis.

The second method is often referred to as the add/remove volume method. When the maximum liquid volume is removed from the drop without the [[interfacial area]] decreasing the receding contact angle is thus measured. When volume is added to the maximum before the interfacial area increases, this is the [[advancing contact angle]]. As with the tilt method, the difference between the advancing and receding contact angles is the contact angle hysteresis. Most researchers prefer the tilt method; the add/remove method requires that a tip or needle stay embedded in the drop which can affect the accuracy of the values, especially the receding contact angle.

=== Bubble shape hysteresis ===
The equilibrium shapes of [[Bubble (physics)|bubbles]] expanding and contracting on capillaries ([[Hypodermic needle#Use by non-specialists|blunt needles]]) can exhibit hysteresis depending on the relative magnitude of the [[Maximum bubble pressure method#Maximum bubble pressure method|maximum capillary pressure]] to ambient pressure, and the relative magnitude of the bubble volume at the maximum capillary pressure to the dead volume in the system.<ref name=":0">{{Cite journal|last1=Chandran Suja|first1=V.|last2=Frostad|first2=J. M.|last3=Fuller|first3=G. G.|date=2016-10-31|title=Impact of Compressibility on the Control of Bubble-Pressure Tensiometers|journal=Langmuir|doi=10.1021/acs.langmuir.6b03258|pmid=27798833|issn=0743-7463|volume=32|issue=46|pages=12031–12038}}</ref>   The bubble shape hysteresis is a consequence of gas [[compressibility]], which causes the bubbles to behave differently across expansion and contraction. During expansion, bubbles undergo large non equilibrium jumps in volume, while during contraction the bubbles are more stable and undergo a relatively smaller jump in volume resulting in an asymmetry across expansion and contraction. The bubble shape hysteresis is qualitatively similar to the adsorption hysteresis, and as in the contact angle hysteresis, the interfacial properties play an important role in bubble shape hysteresis.

The existence of the bubble shape hysteresis has important consequences in [[Surface rheology|interfacial rheology]] experiments involving bubbles. As a result of the hysteresis, not all sizes of the bubbles can be formed on a capillary. Further the gas compressibility causing  the hysteresis leads to unintended complications in the phase relation between the applied changes in interfacial area to the expected interfacial stresses. These difficulties can be avoided by designing experimental systems to avoid the bubble shape hysteresis.<ref name=":0" /><ref>{{Cite journal|last1=Alvarez|first1=Nicolas J.|last2=Walker|first2=Lynn M.|last3=Anna|first3=Shelley L.|date=2010-08-17|title=A Microtensiometer To Probe the Effect of Radius of Curvature on Surfactant Transport to a Spherical Interface|journal=Langmuir|volume=26|issue=16|pages=13310–13319|doi=10.1021/la101870m|pmid=20695573|issn=0743-7463}}</ref>

===Adsorption hysteresis===
Hysteresis can also occur during physical [[adsorption]] processes. In this type of hysteresis, the quantity adsorbed is different when gas is being added than it is when being removed. The specific causes of adsorption hysteresis are still an active area of research, but it is linked to differences in the nucleation and evaporation mechanisms inside mesopores. These mechanisms are further complicated by effects such as [[cavitation]] and pore blocking.

In physical adsorption, hysteresis is evidence of [[mesoporosity]]-indeed, the definition of mesopores (2–50&nbsp;nm) is associated with the appearance (50&nbsp;nm) and disappearance (2&nbsp;nm) of mesoporosity in nitrogen adsorption isotherms as a function of Kelvin radius.<ref>{{cite book|last1=Gregg |first1=S. J. |last2=Sing |first2=Kenneth S. W. |title=Adsorption, Surface Area, and Porosity|edition=Second|location=London|publisher=[[Academic Press]]|year=1982 |isbn=978-0-12-300956-2}}</ref> An adsorption isotherm showing hysteresis is said to be of Type IV (for a wetting adsorbate) or Type V (for a non-wetting adsorbate), and hysteresis loops themselves are classified according to how symmetric the loop is.<ref>{{cite journal|first1=K. S. W. |last1=Sing |first2=D. H.  |last2=Everett |first3=R. A. W. |last3=Haul |first4=L. |last4=Moscou |first5=R. A. |last5=Pierotti |first6=J. |last6=J. Roquérol |first7=T. |last7=Siemieniewska |journal=[[Pure and Applied Chemistry]] |volume=57|issue=4 |pages=603&ndash;619|year=1985|doi=10.1351/pac198557040603|title=Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984)|s2cid=14894781 |doi-access=free }}</ref> Adsorption hysteresis loops also have the unusual property that it is possible to scan within a hysteresis loop by reversing the direction of adsorption while on a point on the loop. The resulting scans are called "crossing", "converging", or "returning", depending on the shape of the isotherm at this point.<ref>{{cite journal|first1=G. A. |last1=Tompsett  |first2=L. |last2=Krogh |first3=D. W. |last3=Griffin |first4=W. C. |last4=Conner |journal=[[Langmuir (journal)|Langmuir]] |volume=21|issue=8|pages=8214&ndash;8225|year=2005|pmid=16114924|doi=10.1021/la050068y|title=Hysteresis and Scanning Behavior of Mesoporous Molecular Sieves}}</ref>

===Matric potential hysteresis===
The relationship between matric [[water potential]] and [[water content]] is the basis of the [[water retention curve]]. [[Matric potential]] measurements (Ψ<sub>m</sub>) are converted to volumetric water content (θ) measurements based on a site or soil specific calibration curve. Hysteresis is a source of water content measurement error. Matric potential hysteresis arises from differences in wetting behaviour causing dry medium to re-wet; that is, it depends on the saturation history of the porous medium. Hysteretic behaviour means that, for example, at a matric potential (Ψ<sub>m</sub>) of {{nowrap|5 kPa}}, the volumetric water content (θ) of a fine sandy soil matrix could be anything between 8% and 25%.<ref>{{cite mailing list |url=http://www.sowacs.com/archives/99-04/msg00000.html |title=Subject: Accuracy of capacitance soil moisture ... |date=8 April 1999 |access-date=28 September 2011 |mailing-list=SOWACS |last1=Parkes |first1=Martin |url-status=dead |archive-url=https://web.archive.org/web/20110928150928/http://www.sowacs.com/archives/99-04/msg00000.html |archive-date=28 September 2011 }}</ref>

[[Tensiometer (soil science)|Tensiometer]]s are directly influenced by this type of hysteresis. Two other types of sensors used to measure soil water matric potential are also influenced by hysteresis effects within the sensor itself. Resistance blocks, both nylon and gypsum based, measure matric potential as a function of electrical resistance. The relation between the sensor's electrical resistance and sensor matric potential is hysteretic. Thermocouples measure matric potential as a function of heat dissipation. Hysteresis occurs because measured heat dissipation depends on sensor water content, and the sensor water content–matric potential relationship is hysteretic. {{As of|2002}}, only desorption curves are usually measured during calibration of [[soil moisture sensors]]. Despite the fact that it can be a source of significant error, the sensor specific effect of hysteresis is generally ignored.<ref>
{{Cite book
 |last1=Scanlon|first1=Bridget R.|author1-link= Bridget Scanlon
 |last2=Andraski|first2=Brian J.
 |last3=Bilskie|first3=Jim
 |year=2002 
 |chapter=3.2.4 Miscellaneous methods for measuring matric or water potential 
 |title=Methods of Soil Analysis: Part 4 Physical Methods
 |publisher=Soil Science Society of America 
 |series=SSSA Book Series
 |pages=643&ndash;670 
 |isbn=978-0-89118-893-3 
 |chapter-url=http://www.beg.utexas.edu/environqlty/vadose/pdfs/webbio_pdfs/Chapt3-2-4.pdf 
 |access-date=2006-05-26 
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