高中物理题1.Howisthegravitationalforcebetweentwomassiveobjectssimilartoanddifferentfromtheelectricforcebetweentwochargedobjects?2.Placeafridgemagnet(F)onthedoorofarefrigerator(R).HowdoweknowthatF,butnotR,

贺知明回答：

　　1.问的是两个物体问的引力,与两个带电电荷间的electricforce的相同与不同.其实就是想要你去比较两条公式.

　　solution:

　　accordingtoNewton'slawofuniversalgravitation,gravitationalforcebewtwwntwomassiveobjects

　　F=G(M1M2/r^2)

　　accordingtoCoulomb'slaw,whichdescribestheinteractionofelectriccharges

　　F=1/(4Лε）(q1q2/r^2)

　　Similaritiesbetweenelectrostaticandgravitationalforces:

　　1.Bothactinavacuum.

　　2.Botharecentralandconservative.

　　3.Bothobeyaninverse-squarelaw(bothareinverselyproportionaltosquareofr).

　　4.Bothpropagatewithfinitespeedc.

　　Differencesbetweenelectrostaticandgravitationalforces:

　　1.Electrostaticforcesaremuchgreaterthangravitationalforces(byabout1036times).

　　2.Gravitationalforcesareattractiveforlikecharges,whereaslectrostaticforcesarerepulsiveforlikecharges.

　　3.Therearenonegativegravitationalcharges(nonegativemass)whiletherearebothpositiveandnegativeelectriccharges.Thisdifferencecombinedwithpreviousimpliesthatgravitationalforcesarealwaysattractive,whileelectrostaticforcesmaybeeitherattractiveorrepulsive.

　　4.Electricchargeisinvariantwhilerelativisticmassisn't

　　2.这条问,把磁铁靠近冰箱的门,磁铁会粘在门上,为什么说磁铁是永久的磁体而冰箱不是.其实是要求你知道sourceofapermanentmagneticfield的定义.

　　答案是：Permanentmagnetsareobjectsthatproducetheirownpersistentmagneticfields.Allpermanentmagnetshavebothanorthandasouthpole.Regularpinsarenotattractedbythedooroftherefrigeratorbutareattractedbyfridgemagnet.

　　3.在某一瞬间,一个媒介,例如,一条绳子,是平的.是不是代表有这个媒介上没有波?

　　波可分为横波纵波,这条绳子上的波可以是纵波,所以看上去上平的.有些波的波长是肉眼看不出来的（例如声波）.不能因为看上去是平的就认为没有波的传递.