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高中物理题1.Howisthegravitationalforcebetweentwomassiveobjectssimilartoanddifferentfromtheelectricforcebetweentwochargedobjects?2.Placeafridgemagnet(F)onthedoorofarefrigerator(R).HowdoweknowthatF,butnotR,
1人问答
更新时间:2024-03-28 21:19:11
问题描述:

高中物理题

1.Howisthegravitationalforcebetweentwomassiveobjectssimilartoanddifferentfromtheelectricforcebetweentwochargedobjects?

2.Placeafridgemagnet(F)onthedoorofarefrigerator(R).HowdoweknowthatF,butnotR,isthesourceofapermanentmagneticfield?Youmaywanttoexperimentwithsomepins,staples,orpaperclipstoproveyourpoint.

3.Supposeatoneinstantthatamediumsuchasastringappearsflat.Doesthismeanthattherearenowavespropagatinginthemedium?

麻烦各位用英文来解释答案

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.
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