IB国际文凭课程物理选修部分总结.doc

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1、IB国际文凭课程物理选修部分总结　　BENGINEERINGPHYSICS1PHYSICSFORTHEIBDIPLOMA?CAMBRIDGEUNIVERSITYPRESSxxOptionBEngineeringphysicsB1RotationaldynamicsInthemechanicswehavestudiedsofar,wehaveassumedthatweweredealingwithpointmasses.Aforceappliedtoapointmasswillaelerateit.However,thingschangewh

2、enwedealwithextendedbodiessuchascylindersandspheres.Forceswillnotonlyaelerateabody’scentreofmassbutmayalsomakethebodyrotate.B1.1KinematicsFigureB.1showsabodythatrotatesaroundanaxisthatisperpendiculartotheplaneofthepaper.IntimeΔtthebodysweepsoutanangleΔθ.Wedefiheaverageangu

3、larvelocityofthebodytobe:ω=ΔθΔ?tandtheinstantaneousangularvelocitytobe:ω=limΔθΔ?tTheunitofangularvelocityisrads?1.Theangularvelocitywillincreaseordecreaseifthereisangularaeleration.Wedefiheaverageangularaelerationas:α=ΔωΔ?tandtheinstantaneousangularaelerationas:α=limΔωΔ?tT

4、heunitofangularaelerationisrads?2.Weseethatthesedefinitionsarepletelyanalogoustoourdefinitionsoflinearquantities:wehavea‘translation’dictionarybetweenlinearandangularquantities:LinearquantityAngularquantityPosition,sAngle,θLinearvelocity,vAngularvelocity,ωAeleration,aAngul

5、araeleration,αPreciselybecauseofthiscorrespondencebetweenlinearandangularquantities,whereaformulaappliestolinearquantitiesasimilarformulawillapplytotheangularquantities.Thuswehavetherelationss=ut+12at2θ=ωit+12αt2s=u+v2tθ=ωi+ωf2tv=u+atωf=ωi+αtv2=u2+2asωf2=ωi2+2αθΔt→0Δt→0Lea

6、rningobjectives?Understandtorque.?Applytheconditionsofrotationalandtranslationalequilibrium.?Workwiththekinematicequationsforrotationalmotion.?Solveproblemsofrotationaldynamics.?Applyconservationofangularmomentum.?θaxist=?tt=0FigureB.1Abodyrotatingaboutanaxis.ExamtipAngula

7、rvelocityandangularaelerationareactuallyvectorquantities,butwewillnotmakeuseoftheirvectornatureinthiscourse.2PHYSICSFORTHEIBDIPLOMA?CAMBRIDGEUNIVERSITYPRESSxxBENGINEERINGPHYSICSwherethesubscriptsiandfdenoteinitialandfinalvalues,respectively.WesawinTopic6thatangularvelocity

8、ωandlinearvelocityvarerelatedbyv=ωr(FigureB.2).Asimilarrelationholdsbetweenangularandline