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1、7NEWTON’STHIRDLAWConceptualQuestions7.1.Ifyouweretothrowtherocksintheoppositedirectionyouwantedtogo,youwouldbepushedbytherocksintherightdirection.Throwingtherocksrequiresaforcetoacceleratethem(Newton’ssecondlaw).Soyouexertaforceontherockinonedirectionandtherockexerts
2、anequalforceonyouintheoppositedirection(Newton’sthirdlaw).Thisforcewillcauseyoutoslidealongtheiceintheoppositedirectionthatyouthrewtherock.Notethatyouwillmovemostefficientlywhenyouuseahorizontalforce,whichmeansthatyouthrowtherockhorizontally.7.2.Thepaddle,you,andthec
3、anoecanbetreatedasasingleobject.Youcanpushbackwardonthewaterwiththepaddlesothatthewaterpushesforwardonthepaddle.Thefigureshowshowthebackwardforceofthepaddleonthewaterandtheforwardforceofthewateronthepaddleareaction/reactionpairs.Sinceyouholdthepaddlewhilesittinginthe
4、canoe,theforceofthewateronthepaddlecausesthepaddle-person-canoeobjecttomoveforward.Theverticalforcebetweenthecanoeandwaterwelabelasanormalforceherebutwilllateridentifyasthebuoyantforce.?Copyright2013PearsonEducation,Inc.Allrightsreserved.Thismaterialisprotectedundera
5、llcopyrightlawsastheycurrentlyexist.Noportionofthismaterialmaybereproduced,inanyformorbyanymeans,withoutpermissioninwritingfromthepublisher.7-17-2Chapter77.3.Therocketforcestheexhaustgasesdown,andthehotgasespushupontherocket.ThetwoforcesareaNewton’sthirdlawpair.Thero
6、cketacceleratesupwardbecausetheforceoftheexhaustgasesontherocketisgreaterthantheforceofgravity.7.4.Theplayerpushesdownonthefloor,whichpushesbackuponhim.Theplayeracceleratesupwardbecausetheforceofhispushisgreaterthantheforceofgravity.7.5.Newton’sthirdlawtellsusthatthe
7、forceofthemosquitoonthecarhasthesamemagnitudeastheforceofthecaronthemosquito.7.6.Themosquitohasamuchsmallermassthanthecar,sothemagnitudeoftheinteractionforcebetweenthecarandmosquito,althoughequaloneach,causesthemosquitotohaveamuchlargeracceleration.Infact,theaccelera
8、tionisusuallyfataltothemosquito.7.7.Newton’sthirdlawtellsusthatthemagnitudeoftheforcesareequal.Theaccelerationofthetruckandcararede
