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1、动量MomentumAfamousdebateaboutmovementInphysicshistory,thereisafamousdebateaboutmovement.Inthe17thcentury,scientistsweretryingtofindacommonphysicalquantityasameasureofthemovement.Somepeopleputthattheproductofthemassandvelocity(速度)oftheobjectshouldmeasurethemovement.Descartesisthemostfamousscientis
2、tofthem.Heputforwardaprinciplethattheamountofmovementintheuniverseisconserved.mvVS1/2mv^2putforward提出,建议putforwardasuggestionNewtonagreedwithitandstudiedfurther.LaterthisprincipledevelopedastheLawofconservationofmomentum.Whileotherpeoplearguedthattheproductofitsmassandthesquare（平方）ofitsvelocitys
3、houldbethemeasureofthemovement.GermanyscientistLeibnizbelieved“mv”didn’tfollowtheLawoffreefall.Thistheorylaterdevelopedaskineticenergy(动能).SomeWordsaboutphysicsmomentum动量mass质量velocity速度speed速率force力gravity重力energy能量kineticenergy动能gravityn.1.严肃庄重saywithsuddengravity2.严重性重要性thegravityofthesituati
4、oninternal energy内能mechanicalenergy机械能pressure压力,压强work功power功率law of conservation of energy能量守恒定律theNewtonsecondlaw牛顿第二定律thetheoryofrelativity相对论momentum（动量）Momentumistheproduct（乘积）ofthemassandvelocity(速度)ofanobject.Forexample,aheavytruckmovingquicklyhasalargemomentum—ittakesalargeforce（力）toget
5、thetruckuptothisspeed,andittakesalargeforcetobringittostop.Ifthetruckwerelighter,ormovingmoreslowly,thenitwouldhavelessmomentum.Likevelocity,momentumalsopossessesadirection.Forexample,amodelairplaneof1kg,travelingduenorthat1m/sinstraightandlevelflight,hasamomentumof1kg·m/sduenorthmeasuredfromthe
6、ground.thelawofconservationofmomentumInaclosedsystem(onethatisnotactedonbyoutsideforces),thetotalmomentumisconserved（不变的）.Thisfactisknownasthelawofconservationofmomentum,whichisimpliedbyNewtonsecondlaw.acton对...起作用，按照...行动actonsb’sadviseSuppose,forexample,thattwoobjectsinteract.Becauseofthethird
7、law,theforcesbetweenthemareequalandopposite.Iftheobjectsarenumbered1and2,thesecondlawstatesthat:Thislawholdsnomatterhowmanytheforcesare.Similarly,ifthereareseveralobjects,thetotalchangeinmomentumiszero.Itcanalsobeusedintheth
