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== Pregled ==
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Kad se elastični materijal deformiše ulsed dejstva spoljašnje sile, it experiences internal resistance to the deformation and restores it to its original state if the external force is no longer applied. There are various [[Elastic modulus|elastic moduli]], such as [[Jangov modul]], the [[shear modulus]], and the [[bulk modulus]], all of which are measures of the inherent elastic properties of a material as a resistance to deformation under an applied load. The various moduli apply to different kinds of deformation. For instance, Young's modulus applies to extension/compression of a body, whereas the shear modulus applies to its [[Shearing (physics)|shear]].<ref>Landau LD, Lipshitz EM. Theory of Elasticity, 3rd Edition, 1970: 1–172.</ref> Young's modulus and shear modulus is only for solids where [[bulk modulus]] is for solid,liquid and gas.
 
Kad se elastični materijal deformiše usled dejstva spoljašnje sile, on doživljava unutrašnju otpornost na deformacije i vraća je u prvobitno stanje ako se spoljašnja sila više ne primjenjuje. Postoje razni [[Elastic modulus|moduli elastičnosti]], kao što je [[Jangov modul]], [[shear modulus|modul smicanja]]<ref>{{GoldBookRef|title=shear modulus, ''G''|file=S05635}}</ref> i [[modul stišljivosti]],<ref>{{cite web|url=http://hyperphysics.phy-astr.gsu.edu/hbase/permot3.html|title= Bulk Elastic Properties|work=hyperphysics|publisher=Georgia State University}}</ref> svi od kojih su mere svojstvenih elastičnih karakteristika materijala kao otpornosti na deformaciju pod primenjenim opterećenjem. Razni moduli se koriste za različite vrste deformacija. Na primer, Jangovi moduli se koriste za istezanje/kompresiju tela, dok se moduli smicanja primenjuju na [[Shearing (physics)|smicanje]] materijala.<ref>Landau LD, Lipshitz EM. Theory of Elasticity, 3rd Edition, 1970: 1–172.</ref> Jangovi moduli i moduli smicanja se koriste samo za čvrste materijale, dok su moduli stišljivosti primenljivi za sva agregatna stanja.
The elasticity of materials is described by a [[stress–strain curve]], which shows the relation between [[stress (mechanics)|stress]] (the average restorative internal [[force]] per unit area) and [[Strain (engineering)|strain]] (the relative deformation).<ref>{{cite book|last=Treloar|first=L. R. G.|title=The Physics of Rubber Elasticity|year=1975|publisher=Clarendon Press|location=Oxford|isbn=978-0-1985-1355-1|page=2}}</ref> The curve is generally nonlinear, but it can (by use of a [[Taylor series]]) be approximated as linear for sufficiently small deformations (in which higher-order terms are negligible). If the material is [[isotropic]], the linearized stress–strain relationship is called [[Hooke's law]], which is often presumed to apply up to the elastic limit for most metals or crystalline materials whereas nonlinear elasticity is generally required to model large deformations of rubbery materials even in the elastic range. For even higher stresses, materials exhibit [[Plasticity (physics)|plastic behavior]], that is, they deform irreversibly and do not return to their original shape after stress is no longer applied.<ref>{{cite book|last=Sadd|first=Martin H.|title=Elasticity: Theory, Applications, and Numerics|year=2005|publisher=Elsevier|location=Oxford|isbn=978-0-1237-4446-3|page=70}}</ref> For rubber-like materials such as [[elastomer]]s, the slope of the stress–strain curve increases with stress, meaning that rubbers progressively become more difficult to stretch, while for most metals, the gradient decreases at very high stresses, meaning that they progressively become easier to stretch.<ref>{{cite book|last=de With|first=Gijsbertus|title=Structure, Deformation, and Integrity of Materials, Volume I: Fundamentals and Elasticity|year=2006|publisher=Wiley VCH|location=Weinheim|isbn=978-3-527-31426-3|page=32}}</ref> Elasticity is not exhibited only by solids; [[non-Newtonian fluid]]s, such as [[Viscoelasticity|viscoelastic fluids]], will also exhibit elasticity in certain conditions quantified by the [[Deborah number]]. In response to a small, rapidly applied and removed strain, these fluids may deform and then return to their original shape. Under larger strains, or strains applied for longer periods of time, these fluids may start to flow like a [[viscosity|viscous]] liquid.
 
Elastičnost materijala se opisuje pomoću [[stress–strain curve|dijagrama naprezanja]],<ref>Luebkeman, C., & Peting, D. (2012, 04 28). Stress–strain curves. Retrieved from http://pages.uoregon.edu/struct/courseware/461/461_lectures/461_lecture24/461_lecture24.html.</ref> koji prikazuje relaciju između [[Напон (механика)|napona]] (prosečne restorativne unutrašnje [[Сила|sile]] po jedinici površine) i [[Deformation (engineering)|naprezanja]] (relativne deformacije).<ref>{{cite book|last=Treloar|first=L. R. G.|title=The Physics of Rubber Elasticity|year=1975|publisher=Clarendon Press|location=Oxford |isbn=978-0-1985-1355-1 |page=2}}</ref> Kriva je generalno nelinearna, ali ona može da bude aproksimirana (pomoću [[Taylor series|Tejlorove serije]]) kao linearna za dovolno male deformacije (kod kojih su članovi višeg reda zanemarljivi). Ako je materijal [[Isotropy|izotropan]], linearizovana relacija naprezanja se naziva [[Hukov zakon]], za koji se obično podrazumeva da važi do elastičnog limita za većinu metala ili kristalnih materijala, dok je nelinearna elastičnost generalno neophodna za modelovanje velikih deformacija ili gumenih materijala čak i u elastičnom opsegu. Pri još većim naponima, materijali ispoljavaju [[Plasticity (physics)|plastično ponašanje]], to jest, oni se nepovratno deformišu i ne vraćaju se u svoj prvobitni oblik nakon što se stres više ne primenjuje.<ref>{{cite book|last=Sadd|first=Martin H.|title=Elasticity: Theory, Applications, and Numerics|year=2005|publisher=Elsevier|location=Oxford|isbn=978-0-1237-4446-3|page=70}}</ref> Za gumaste materijale kao što su [[elastomer]]i, nagib dijagrama naprezanja se povećava sa naponom, tako da je gumu progresivno sve teže dalje istezati, dok se za većinu metala gradijent smanjuje pri veoma visokim napnima, tako da oni progresivno postaju sve rastegljiviji.<ref>{{cite book|last=de With|first=Gijsbertus|title=Structure, Deformation, and Integrity of Materials, Volume I: Fundamentals and Elasticity|year=2006|publisher=Wiley VCH|location=Weinheim|isbn=978-3-527-31426-3|page=32}}</ref> Elastičnost ne manifestuju samo čvrsti materijali; [[non-Newtonian fluid|nenjutnovski fluidi]],<ref name=springer2>{{cite book| title=Springer handbook of experimental fluid mechanics |first1=Cameron |last1=Tropea |first2=Alexander L. |last2=Yarin |first3=John F. |last3=Foss |publisher=Springer |year=2007 |isbn=978-3-540-25141-5 |pages= |url=https://books.google.com/books?id=y0xDUAdQAlkC&lpg=PA669&dq=thixotropic&pg=PA667#v=onepage&q=thixotropic&f=false}}</ref> kao što su [[Viscoelasticity|viskoelastični fluidi]],<ref name=Meyers>Meyers and Chawla (1999): "Mechanical Behavior of Materials", 98-103.</ref> isto tako ispoljavaju elastičnost u pojedinim uslovima kvantifikovanim [[Deborah number|Deborovim brojem]].<ref name="Reiner1964">{{citation|first=M. |last=Reiner |year=1964|journal=Physics Today|volume =17|issue= 1| page= 62 |title=The Deborah Number|doi=10.1063/1.3051374|bibcode = 1964PhT....17a..62R }}</ref><ref>[http://rrc.engr.wisc.edu/deborah.html The Deborah Number] {{webarchive|url=https://web.archive.org/web/20110413144406/http://rrc.engr.wisc.edu/deborah.html |date=2011-04-13 }}</ref> U responsu na mala, brzo naneta i uklonjena naprezanja, te tečnosti mogu da budu deformisane i da se vrate u svoj prvobitni oblik. Pod većim naprezanjima, ili naprezanjima primenjenim tokom dužih vremenskih perioda, ovi fluidi mogu da počnu da teku kao [[viscosity|viskozne]] tečnosti.
 
== Hukov zakon ==
Преузето из „https://sr.wikipedia.org/wiki/Elastičnost_(fizika)”