Whatarewaves?
Farouttosea,thewinddisturbsthecalmsurfaceofthewater.Arippleforms.Asthewind
continuestoblow,theripplegrowsintoapowerfulwavethatcantravelagreatdistance.Nearthebeach,
surferswaiteagerly.Theyquicklypaddleintodeeperwatertocatchthemonstrouswave.Surfersenjoy
thepowerofnatureastheyridethewavetotheshore.
Whatarewaves?Howcantheytravelsofar?Whyaresomewavesmorepowerfulthanothers?In
thissection,youwillexplorehowwavesbeginandhowtheymove.
WavesandEnergy
Wavescrashingonabeachshowthetremendousenergywaves
cancarry.Awaveisdisturbancethattransfersenergyfromplaceto
place.Inscience,energyisdefinedastheabilitytodowork.To
understandwaves,thinkofaboatoutontheocean.Ifawavedisturbsthe
surfaceofthewater,itwillcauseanythingfloatingonthewatertobe
disturbed,too.Theenergycarriedbyawavecanliftevenalargeshipasit
passes.
Thedisturbancecausedbyawaveistemporary.Afterthewave
haspassed,thewateriscalmagain.
WhatCarriesWaves?Manywavesrequiresomethingtotravelthrough.
Waterwavestravelalongthesurfaceofthewater,andsoundwaves
travelthroughair.Youcanevenmakeawavetravelalongarope.The
materialthroughwhichawavetravelsiscalledamedium.Gases(suchas
air),liquids(suchaswater),andsolids(suchasropes)allactasmediums.
Wavesthatrequireamediumthroughwhichtotravelarecalled
mechanicalwaves.
Althoughwavestravelthroughamedium,theydonotcarrythemediumitselfwiththem.Lookat
theduckinpicture.Whenawavesmovesundertheduck,theduckmovesupanddown.Itdoesnotmove
alongthesurfaceofthewater.Afterthewavespasses,thewaterandtheduckreturntowherethey
started.
Breakingwavesatabeachbehavealittledifferently.Whenwaveshitabeach,thewaterdoes
movealongwiththewave.Thishappensbecausetheoceanfloornearthebeachslopesupward.Asthe
wateratthebottomofthewavehitstheslope,itmovesuptowardthetopofthewave.Thetopofthe
wavegetsbiggerandcontinuestomoveforward.Eventuallyittopplesover,turningwhiteandfrothy.
Notallwavesrequireamediumtocarrythemalong.Lightfromthesun,forexample,cantravel
throughemptyspace.Lightisanexampleofanelectromagneticwave.
WhatCausesWaves?Youcancreatewavesbydippingyourfingerinwater.Wavesarecreatedwhena
sourceofenergycauseamediumtovibrate.Avibrationisarepeatedbackandforthorupanddown
motion.Thismotionisthewave.
TypesofWaves
Differenttypesofwavestravelthroughmediumsindifferentways.Wavesareclassifiedaccordingto
howtheymove.Thethreetypesofwavesaretransversewaves,longitudinalwavesandsurfacewaves.
TransverseWaves:
Whenyoumakeawaveonarope,thewavemovesfromoneendoftheropetotheother.Theropeitself,
however,movesupanddownorfromsidetoside.Wavesthatmovethemediumatrightanglestothe
directioninwhichthewavesaretravelingarecalledtransversewaves.Transversemean“across.”Asa
transversewavemovesinonedirection,the
particlesofthemediummoveacrossthe
directionofthewave.Theimageontheright
showsthatsomepartsoftheropeareveryhigh
whilesomeareverylow.Thehighestpartofthe
wavearecalledcrests,andthelowestpartsare
calledtroughs.
LongitudinalWaves.Figure3showsadifferent
kindofwave.Ifyoustretchoutaspringtoyand
pushandpulloneend,youcanproducea
longitudinalwave.Longitudinalwavesmovetheparticlesofthemediumparalleltothedirectionin
whichthewavesaretravel.Thecoilsinthespringmovebackandforthparalleltothewavemotion.
Noticeinpictruethatinsomepartsof
thespringthecoilsareclosetogether.Inother
parts,thecoilsaremorespreadout.Theparts
wherethecoilsareclosetogetherarecalled
compression.Thepartswherethecoilsare
spreadout,orrarefied,arecalledrarefactions.
Ascompressionsandrarefactionstravel
alongthespringtoy,eachcoilmovesslightly
forwardandthenback.Theenergytravels
fromoneendofthespringtotheother,
creatingawave.Afterthewavepasses,each
partofthespringreturnstothepositionwhereitstarted.
Combinationsofwaves.Surfacewavesarecombinationsoftransverseandlongitudinalwaves.These
wavesoccuratthesurfacebetweentwomediums,suchaswaterandair.Whenawavepassesthrough
water,thewater(andanythingonit)movesupanddown,likeatransversewaveonarope.Thewater
alsomovesbackandforthslightlyinthedirectionthatthewaveistraveling,likethecoilsofthespring.
Butunlikethecoilsofaspring,waterdoesnotcompress.Theupanddownandbackandforth
movementscombinetomakeeachparticleofwatermoveinacircle.Figure4showsthecircularmotion
ofsurfacewaves.