Energy&Work

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1、WorkandEnergyKineticEnergyWorkdonebyforcesWork-KineticEnergytheoremConservationofkineticenergyKineticenergyincollisionConservativeForcesandPotentialEnergyConservationofMechanicalEnergyEnergyEnergyisascalarquantityassociatedwiththestateofasystem.Itisatrulyfundamentalanduniversalconceptinphysics.En

2、ergyisanumberthatdescribesthestateofaphysicalsysteminasimilarwayasGDPreflectstheeconomicalactivitiesofacountryorasmoneyinthebankreflectsyourfinancialcondition.Astateofamechanicalsystemcanalsobespecifiedbythemass,positionandvelocityofallthebodieswithin.Forexample,ifforceschangeoneormoreoftheobject

3、sinasystembymakingthemmove,thenthestateofthesystemchanges.Itisfareasiertokeeptrackofthestatebykeepingtrackoftheenergythankeepingtrackofallthepositionsandvelocities.Themethodofassigningenergyhastobeplannedcarefullyforittoproperlyreflectthestateofasystem.Onceproperlydefined,energycanbeusedtoandtopl

4、acelimitsonorpredicttheoutcomesofexperiments.PrincipleofconservationofenergyEnergycanbetransformedfromonetypetoanotherandtransformedfromanobjecttoanother,butthetotalamountisthesame(energyisconserved).Noexceptiontothisprinciplehasbeenfound.Historically,newformsofenergyhadtobedefinedandaddedtokeept

5、heprincipleintact.KineticEnergyKineticenergyKofanobjectisassociatedwiththestateofmotionoftheobject.Foranobjectofmassmspeedv,wellbelowthespeedoflight,itisdefinedas12Kmv.222TheSIunitofenergyisjoule(J).1J=1kg.m/s.22e.g.A3.0kgduckflyingat2.0m/shasakineticenergyof6.0kg.m/s=6J.Whenthereismorethanoneob

6、jectinasystem,thekineticenergyofthesystemisgivenbyn12thKmiiv,wheremiandviarethemassandthespeedoftheiobject.2iWorkWorkWistheenergytransfertoorfromanobjectbyaforceFactingonit.Wesaytheworkdoneontheobjectbytheforceispositiveifenergyistransferredtotheobject.Energytransferredfromtheobjectisnegativewo

7、rk.Note:donotconfusethescientificmeaningofworkwithitsmeaningincommonlanguageusage.WorkandKineticEnergyConsideraparticlemassmsituatedatapositionSrrt:()vectorrandisactedonbyanetforceF.Inthecourseoftime,thepartic