lec13-Momentum Conservation

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1、PhysicsI-Class13ConservationofMomentum1ParticleMomentumTheimpulse-momentumtheoremrevealsaconservationlawforparticlemotion:WhenF=0,theparticlemomentumisconstant.netRemarkably,momentumisalsoconservedforasystemofparticles!2MomentumConservationforaSystemofObjectsThesystemsweareinterestedinarecollect

2、ionsofobjectsthathavenegligibleinteractionwithobjectsoutsidethesystem.Momentumisconservedwithinthesystemaslongasthesystemstaysisolatedsuchthatnoexternalforcesactonthesystem..Examples:Solarsystem,atom,molecule,etc.Ifthereareexternalforces,thenthetotalmomentumofthesystemconsistingofthemomentumofeac

3、hpartchangesby3InternalandExternalForcesHowdotheselabelschangeifweisolateObjectAasthesystem?4TheMomentumofaSystem5CancellationofInternalForces6ConservationofMomentum7Ex:TwoCartsonaTrack8MomentumConservationinThreeDimensions9CollisionsinTwoDimensions102-DCollisions11CenterofMassThecenterofmassisth

4、eaveragepositionofallthemasses:12Example:TwoObjects13CenterofMass,SystemMomentum,andSystemVelocity14Take-AwayConcepts15Take-AwayConcepts16Problem1oftheDay17Problem2oftheDayProblem2oftheDayvMmcmVdHowfaristhecmfromm?Howfaristhecmfromm?HowfaristhecmfromM?HowfaristhecmfromM?HowfarismfromM?Howfarism

5、fromM?Whatistheimpulseonmingoinghalfwayaround?Whatistheimpulseonmingoinghalfwayaround?1818Solution:1mxcm=(mxm+MxM)=0⇒xM=−xmm+MMdmdx=−⇒x=mM2M2mdΔx=x−x=1+mMMmM206-19