motion and equilibrium tenafly public schools index旋转运动和平衡特纳夫莱公立学校指数课件_1

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1、TorqueandAngularAccelerationAPPhysicsCMrs.Coylehttp://mdmetric.com/tech/torqueB.gifTorque,t:Thetendencyofaforcetorotateanobjectaboutanaxis.Vectorquantitythatisthecrossproductofthelever(momentarm)andtheforce.t=r┴xF=rFsinfristheperpendiculardistancebetweentheaxisofrotationandthefor

2、ce.SignofTorqueIftherotationcausedbythetorqueistendingtobecounterclockwisethetorqueispositive.Iftherotationcausedbythetorqueistendingtobeclockwisethetorqueisnegative.Thedirectionoftorqueisfoundbytherighthandrule.Thefingerswrapinthedirectionoftheforce.Thethumbrepresentsthetorqueve

3、ctor.DirectionofTorqueUnitsofTorqueUnit:m·NNote:theunitsarethesameasthatofenergy,butarenotequivalent,theyarenotaJoule.Equilibrium:TranslationalSF=0RestorConstvRotationalSt=0NorotationorconstwMechanicalEquilibriumBothoftheaboveStaticEquilibriumStaticTranslationalandStaticRotationa

4、lNoTranslation,norotationExample:WheelTwoforcesareactingonawheelasshown.Findthetorquesproducedbyeach.Inwhichdirectionwillthewheelturn?Isthererotationalequilibrium?r=0.3mTorqueandAngularAccelerationTangentialforceFt=matTorqueτ=Ftr=matrτ=mαrr=mr2ατ=IαTorqueandAngularAccelerationFo

5、ranelementalparticledmSt=IaNoteSt=IaisanalogoustoSF=maEx:WheelEx:TwoPulleysEx:TwoPulleyscont’dNote:Nandmgdonotsupplyatorquebecausetheyactthroughthecenterofrotation.Ex:#34Agrindingwheelisintheformofauniformsoliddiskofradius7.00cmandmass2.00kg.Itstartsfromrestandacceleratesuniforml

6、yundertheactionoftheconstanttorqueof0.600Nmthatthemotorexertsonthewheel.Howlongdoesthewheeltaketoreachitsfinaloperatingspeedof1200rev/min?Throughhowmanyrevolutionsdoesitturnwhileaccelerating?Ans:a)1.03s,b)10.3revEx:#38Apotter’swheel-athickstonediskofradius0.500mandmass100kg-isfr

7、eelyrotatingat50rev/min.Thepottercanstopthewheelin6.00sbypressingawetragagainsttherimandexertingaradiallyinwardforceof70.0N.Findtheeffectivecoefficientofkineticfrictionbetweenthewheelandrag.Ans:0.312