人教版英语八年级下unit9 课件5

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1、全品秦老师英语课堂CircularmotionHaveyoueverbeentoanamusementpark?Fig.05.19WhysomebodyneedstoknowaboutcircularmotionOtherwisewewouldn’tgoonthoserides?Spacestation,satellites,livefromoverseasPlanets,CometsandMoonsUniformCircularMotionVelocityisavector,ithasbothdire

2、ctionandmagnitudeSimplestcase:directionconstant,magnitudechanges.LinearMotionWewillnowstudyanother“simple”case:magnitudeisconstantanddirectioncontinuallychanges.UniformCircularMotion8CircularMotionXθ=0yifHowdowelocatesomethingonacircle?Giveitsangularp

3、ositionθWhatisthelocationof900orπ/29CircularMotionistheangularposition.Angulardisplacement:Note:anglesmeasuredClockwise(CW)arenegativeandanglesmeasured(CCW)arepositive.ismeasuredinradians.2radians=360=1revolutionxyifWhatisaradian?C=2πr=(totalangle

4、ofonerotation)xrRadianmeasurerelatesdisplacementalongcircumferencetoangulardisplacement11CircularMotionXθ=0yifHowdowelocatesomethingonacircle?GiveitsangularpositionθWhatisthelocationof900orπ/2Fromθ=0toθ=900wehavegone¼ofwayaround¼of2π=π/212xyifrarc

5、length=s=risaratiooftwolengths;itisadimensionlessratio!ThisisaradianmeasureofangleIfwegoallthewayrounds=2πrandΔθ=2πQuestionAchildrunsaroundthecircularledgeofafountainwhichhasadiameterof6.5m.Afterthechildhasrun9.8m,herangulardisplacementisA)0.48rad.B)6

6、.0rad.C)1.5rad.D)3.0rad.14Ifwemovearoundacirclewechangeθ.Howfastdoesθchange?Theaverageandinstantaneousangularvelocitiesωare:ismeasuredinrads/sec.vandωForcircularmotion—HowfardoyoutravelduringΔtifyouarespinningatanangularvelocityω?Howfar?s=Δθr=ωΔtrHowfast

7、?(speed)v=s/Δt=ωrv=ωrQuestionAchildrunsaroundthecircularledgeofafountainwhichhasadiameterof6.5m.Ifittakesher72secondstorunallthewayaround,herangularvelocityisA)0.087rad/sB)0.57m/sC)0.17rad/sD)0.044rad/sQuestionACDmakesonecompleterevolutioneverytenthofasec

8、ond.Theangularvelocityofpoint4is:A)thesameasforpt1.B)twicethatofpt2.C)halfthatofpt2.D)1/4thatofpt1.E)fourtimesthatofpt1.QuestionACDmakesonecompleterevolutioneverytenthofasecond.Whichhasthelargestlinear(tangential)ve