newtons惯性大小只与质量有关

NEWTON’SLAWSOFMOTION1SATIIphysicstestWhatis

force？？？3Newton’sFirstLawNewton’sFirstLawsaysthatobjectsinmotionwillremaininmotionunlessacteduponbyanexternalforce.Inertia4Inertia惯性大小只与质量有关！惯性是保持物质原有运动状态的属性！5Newton’sSecondLawNetforceonanobjectcausesittoaccelerate.合外力与加速度大小成正比，方向相同静止、匀速直线运动变速运动Fnet=0Fnet≠064m/s2VconstantFrictionnotnegligibleIfF=30NWhatistheacceleration?WhenF=70Nm=8kg5m/s27Newton’sThirdLawAction—reactionprinciple作用力与反作用力，成对出现，方向相反，大小相同8FrictionforceNormalforceTensionWeightfk=μkFnfs≤μsFnKineticStaticFreeBodyDiagrams：9Ifa20Nforceduewestcreatesanaccelerationof3m/s2,whatistheaccelerationifthemassoftheobjectisdoubled.1.5ms-2inthewestdirectionFindtheaccelerationandthetensioninthestringsUseg=-10m/s2AB6ms-2intheeastdirectionAB6ms-2inthesouthdirectionT=12N101.确定研究对象2.进行受力分析3.矢量分解与求和4.(根据合力确定加速度)有关力与运动的题目a=2gTmWFnT=?11θ1=30°,θ2=45°,m1=20kg,m2=?Fn1=m1gcos30°T=m1gsin30°T=m2gsin45°Fn2=m2gcos45°T=100NFn2=100Nm2=14.1kg12Findthetensions(T1andT2)andtheaccelerationofeachmasswhenaforceFisappliedtomassm1asshowninthediagrambelow.Assumethereisnofriction.Expressyouranswerintermsofm1,m2,m3,andF.对于同速系统，可以使用整体法13Amanwhohasamassof70kgstandsonthescaleinsidetheelevator.Findthescalereadingforthefollowingconditions.(g=10m/s2):(a.)Theelevatorisatrest.(b.)Theelevatorismovingupwithaconstantaccelerationof2m/s2.(c.)Theelevatorismovingdownwithaconstantaccelerationof2m/s2.(d.)Theelevatorismovingupwithconstantvelocity.(e.)Theelevatorcableiscut.|Fnet|=|mg-N|a70kgb84kgc56kgd70kge0kg14Frictionforce15A3kgblockisplacedontopofa10kgblockasshowninthefigurebelow.Thecoefficientofstaticfrictionbetweenbothblocksis0.5.Whatisthemaximumaccelerationthatthesystemcanhavewithouttoppling?FindthemaximumforceFthatcanbeappliedtothe10kgmass.(Assumethatthereisnofrictionbetweenthe10kgblockandthesurface.)Useg=10m/s2m1m2N2=m2gfs=m2afs=μsN2a=5m/s2N2+m1g=N1F-fs=m1aF=65NF=(m1+m2)a16g=9.8m/s217△y=2.4m；△x=1.8m；d=0.95m；mball