英文版大学物理功和能

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1、Chapter7&8EnergyandConservationLawWorkandPower2.KineticEnergy&Work-EnergyPrinciple3.ConservativeandNonconservativeForces4.PotentialEnergy5.ConservationofEnergy7-1WorkandPower(P147-)Theworkdonebyaforceindisplacingabodyasthescalarproductofand.1.Work研究力和运动的空间过程关系。Workisascalar,nodirection.p

2、ositivework;ConstantForce(includingitsdirection)zerowork;negativework.Explanations:(1)Iftheforceisconstantinthewholepath,ABoABWhenaparticlemovesfromAtoBalongacurvepath,thetotalworkdonebytheforceequalstheintegraloffromAtoB:(2)Workdonebyavaryingforce:—displacementfromAtoBWorkisdependantont

3、hereferenceframe.If(3)Workdonebyseveralforces:(4)Specialexpressioninscalarproduct:Theworkdonebyseveralforces=algebraicsumoftheworkdonebytheindividualforce.(5)Geometricalrepresentationofwork:Fxx1x2dxTheworkdonebyaforceequalstheareaundertheFversusxcurve——变力曲线与位移轴在两点x1,x2之间所包围的面积.(6)Unitofw

4、ork:Dimensionis:MLT–2L=ML2T–2InSIsystem,1N·m=1J(joule)=1kg·m2/s2xFxFxFW=0W<0W>06ExampleCalculatetheworkbytheforcewhentheparticlemovesfromx1=2(m)tox2=3(m)inthefollowingcases:1.Thetrajectoryisaparabola2.ThetrajectoryisastraightlineXYOTheforceontheparticleisWorkdependsonpath.XYOSolution:Int

5、eractionforcebetweenm1andm2Displacementofm1w.r.ttom2Forceonm1bym2WorkofapairofforcesWehaveusedthisconclusionbeforeWorkbypairofnormalforcesWorkbypairoffrictionforces<0Totalworkisnegative.CommonexampleDoyouknowthatitistheresultofworkbypairofforces?2.Power(功率)(P186)Instantaneouspower:Theins

6、tantaneouspowerPisdefinedastherateatwhichworkisperformed.TheSIunitofpoweristhewatt,1W=1J/s1horsepower=1hp=746WabAparticlemovesfromatobalonganarbitrarypath.andmayvaryfrompointtopointalongthepath.dsrThatis,7-2Work-KineticEnergyTheorem(P156-)BecauseWegetWecanalsowritedAasAsAnotherapproach:D

7、educeWeshouldgetusedtothiskindofderivation.Networkdoneonanobjectequalstothechangeinitskineticenergy.Explanations:(1)Workisthemeasurementsforthechangeinthekineticenergy(K)ofabody.——Bodygainsthekineticenergy.—Bodyloses“K”&doesworkoutside.(2)Bothworkand“K”arescalars.Theyhave