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1、.....Chapter9OscillationsWearesurroundedbyoscillations─motionsthatrepeatthemselves.(1).Thereareswingingchandeliers,boatsbobbingatanchor,andthesurgingpistonsintheenginesofcars.(2).Thereareoscillatingguitarstrings,drums,bells,diaphragmsintelephonesandspeakersystems
2、,andquartzcrystalsinwristwatches.(3).Lessevidentaretheoscillationsoftheairmoleculesthattransmitthesensationofsound,theoscillationsoftheatomsinasolidthatconveythesensationoftemperature,andtheoscillationsoftheelectronsintheantennasofradioandTVtransmitters.Oscillati
3、onsarenotconfinedtomaterialobjectssuchasviolinstringsandelectrons.Light,radiowaves,x-rays,andgammaraysarealsooscillatoryphenomena.Youwillstudysuchoscillationsinlaterchaptersandwillbehelpedgreatlytherebyanalogywiththemechanicaloscillationsthatareabouttostudyhere.O
4、scillationsintherealworldareusuallydamped;thatis,themotiondiesoutgradually,transferringmechanicalenergytothermalenergybytheactionoffrictionalforce.Althoughwecannottotallyeliminatesuchlossofmechanicalenergy,wecanreplenishtheenergyfromsomesource.学习参考.....9.1SimpleH
5、armonicMotion1.Thefigureshowsasequenceof“snapshots”ofasimpleoscillatingsystem,aparticlemovingrepeatedlybackandforthabouttheoriginofthexaxis.2.Frequency:(1).Oneimportantpropertyofoscillatorymotionisitsfrequency,ornumberofoscillationsthatarecompletedeachsecond.(2).
6、Thesymbolforfrequencyisf,and(3)itsSIunitishertz(abbreviatedHz),where1hertz=1Hz=1oscillationpersecond=1s-1.3.Period:RelatedtothefrequencyistheperiodTofthemotion,whichisthetimeforonecompleteoscillation(orcycle).Thatis.4.Anymotionthatrepeatsitselfatregularintervalsi
7、scalledperiodmotionorharmonicmotion.Weareinterestedhereinmotionthatrepeatsitselfinaparticularway.Itturnsoutthatforsuchmotionthedisplacementxoftheparticlefromtheoriginisgivenasafunctionoftimeby,in学习参考.....whichareconstant.Themotioniscalledsimpleharmonicmotion(SHM)
8、,thetermthatmeansthattheperiodicmotionisasinusoidaloftime.1.Thequantity,apositiveconstantwhosevaluedependsonhowthemotionwasstarted,iscalledtheamplitudeofthemot
