Wave.ThedifferentMechanicalwaveswaterwavessoundwavesseismicwaves(地震波)Thesewaveshavecertaincentralfeatures:

TheyaregovernedbyNewton’slaws,andtheycanexistonlywithinamaterialmedium,suchaswater,air,androck..1.TransverseWaves(橫波，S波)

Thedirectionofoscillationofmediumelementsisperpendicular(垂直)tothedirectionoftravelofthewave.TwotypeofMechanicalwaves..2.LongitudinalWaves(縱波，P波)

Thedirectionofoscillationofmediumelementsisparallel(平行)tothedirectionofthewave’stravel,themotionissaidtobelongitudinal,andthewaveissaidtobealongitudinalwave.

Bothatransversewaveandalongitudinalwavearesaidtobetravelingwavesbecausetheybothtravelfromonepointtoanother,asfromoneendofthestringtotheotherend.sparseanddense..TheTides1Themoon’sgravityactsontheearthThemoon’sgravityisn’tuniformTheearth’soceansarepulledoutofround.T=24hour48min.TheTides2TherearetwotidalbulgesintheoceansAstheearthrotates,thesebulgesshiftAlmost2highand2lowtidesperdayStrongesttidesnearequatorWeakesttidesnearpoles.TheSun’sInfluenceSun’sgravityaffectstidesStrongesttideswhenmoonandsunarealignedWeakesttideswhenmoonandsunareatrightangles.TidalResonanceWaterinaconfinedchannelcansloshbackandforthAnotherharmonicoscillatorPerioddependsontheinertiadividedbytherestoringforceIfthesloshingtimematchesthetidalperiod,resonanceoccurs.WaterWavesSloshinginvolvesdeepwaterwaves:thewholeliquidmovesbackandforthSurfacewavesonlyaffecttheliquid’stop..Water’sMotionSurfacewatercirclesasthewavepassesCirclingisstrongestatsurfaceMotionisweakabout1/2wavelengthdeep.WaterinaWaveOnlythewavetravels,thewatercirclesCrestsareformedfromlocalwater..Question:Youarefloatingmotionlessinaninnertube.Youarenearabeachbutfarenoughfromtheshorethatwavesaren'tbreakingontopofyou.Youwilldrifttowardshoreatthespeedofthewavesdriftgraduallytowardshorecircleaswavespassbutnotprogresstowardshore..WavelengthThelongerthewavelengthofasurfacewave,thefasterittravelsthedeeperwatermovesasitpassesthemoreenergyitcontainsforagivenamplitudeTsunamis（海嘯）areverylongwavelength,verydeep,veryhighenergywaves.Thepower

oftsunamis.BreakingWavesSurfacewavesslowdowninshallowwaterWavesbunchasthewatergetsshallowerWavesgettallerasthewatergetsshallowerWavesbreakwhenwatercan’tformcrestGraduallyslopingbottom:rollingsurfSteeplyslopingbottom:plungingbreakers..BreakingWavesDoyouhaveanyexamplesofbreakingwave?.Bulwark(防波堤).潮吹孔.SurfingWavesactasmovingramps（斜坡）Forcesonasurfer:Rampforce(Downhill)formedbysumofbuoyantforce（浮力）weightliftDragforce(Uphill)Netforceiszeroduringsteadysurfing.ChangingWaveSpeedsReflection（反射）WavespeedchangecausespartialreflectionThebiggerthechange,themorereflectionRefraction（折射）WavespeedchangecanredirectwaveWavesbendtowardshoreastheyslow.ImportantPropertiesofWaves:Howtochangetheirdirection.ReflectionBounceoffsurface(ormediumofdifferentdensity)RefractionBendtowards“slower”mediumDiffraction（衍射）Bendaroundbarr