Transverse Waves

Canyouguesswhatthispictureshows?Here’sahint:theobjectsinthepicturehavebeenmagnified,andoneofthemismovingrapidly.Theobjectsareguitarstrings,andthemovingstringistheoneonthebottomright.Thestringismovingbecauseithasjustbeenplucked.Pluckingthestringgaveitenergy,whichismovingthroughthestringinamechanicalwave.Amechanicalwaveisawavethattravelsthroughmatter.Thematteramechanicalwavetravelsthroughiscalledthemedium.Thetypeofmechanicalwavepassingthroughthevibratingguitarstringisatransversewave.

What Is a Transverse Wave? Atransversewaveisawaveinwhichparticlesofthemediumvibrateatrightangles,orperpendicular,tothedirectionthatthewavetravels.Anotherexampleofatransversewaveisthewavethatpassesthrougharopewithyoushakeoneendoftheropeupanddown,asintheFigurebelow.Thedirectionofthewaveisdownthelengthoftheropeawayfromthehand.Theropeitselfmovesupanddownasthewavepassesthroughit.

Q:Whenaguitarstringisplucked,inwhatdirectiondoesthewavetravel?Inwhatdirectionsdoesthestringvibrate?A:Thewavetravelsdownthestringtotheend.Thestringvibratesupanddownatrightanglestothedirectionofthewave.Crests and Troughs Atransversewaveischaracterizedbythehighandlowpointsreachedbyparticlesofthemediumasthewavepassesthrough.Thehighpointsarecalledcrests,andthelowpointsarecalledtroughs.Youcanseebothinthefiguretotheright.

S Waves TransversewavescalledSwavesoccurduringearthquakes.Thedisturbancethatcausesanearthquakesendstransversewavesthroughundergroundrocksinalldirectionsawayfromthedisturbance.Swavesmaytravelforhundredsofmiles.AnSwaveismodeledintheFigurebelow

Summary • Atransversewaveisawaveinwhichparticlesofthemediumvibrateperpendicularto

thedirectionthatthewavetravels.• Thehighpointsofatransversewavearecalledcrests,andthelowpointsarecalled

troughs.• Swavesaretransversewavesthattravelthroughundergroundrocksduring

earthquakes. Review

1. Whatisatransversewave?2. Sketchatransversewaveandlabelthecrestsandtroughs.3. InferhowSwavesmightaffectstructuressuchasbuildings.

Longitudinal Waves You’veprobablyplayedwithSlinkyspringtoyslikethese.They’resimpletoys,buttheycanmoveinveryinterestingways.Pushinginontheendofaspringtoy,forexample,givesitenergythatmovesthroughthespringinalongitudinalwave.What Is a Longitudinal Wave? Alongitudinalwaveisatypeofmechanicalwave.Amechanicalwaveisawavethattravelsthroughmatter,calledthemedium.Inalongitudinalwave,particlesofthemediumvibrateinadirectionthatisparalleltothedirectionthatthewavetravels.YoucanseethisintheFigurebelow.Theperson’shandpushesandpullsononeendofthespring.Theenergyofthisdisturbancepassesthroughthecoilsofthespringtotheotherend.

Compressions and Rarefactions NoticeintheFigureabovethatthecoilsofthespringfirstcrowdclosertogetherandthenspreadfartherapartasthewavepassesthroughthem.Placeswhereparticlesofamediumcrowdclosertogetherarecalledcompressions,andplaceswheretheparticlesspreadfartherapartarecalledrarefactions.Themoreenergythewavehas,theclosertogethertheparticlesareincompressionsandthefartheraparttheyareinrarefactions. P Waves EarthquakescauselongitudinalwavescalledPwaves.Thedisturbancethatcausesanearthquakesendslongitudinalwavesthroughundergroundrocksinalldirectionsawayfromthedisturbance.PwavesaremodeledintheFigurebelow.Q:WherearethecompressionsandrarefactionsofthemediuminthismodelofPwaves?A:Thecompressionsaretheplaceswheretheverticallinesareclosesttogether.Therarefactionsaretheplaceswheretheverticallinesarefarthestapart.

Summary

• Alongitudinalwaveisatypeofmechanicalwave,orwavethattravelsthroughmatter,calledthemedium.Inalongitudinalwave,particlesofthemediumvibrateinadirectionthatisparalleltothedirectionthatthewavetravels.

• Placeswhereparticlesofthemediumcrowdclosertogetherarecalledcompressions.Placeswhereparticlesofthemediumspreadfartherapartarecalledrarefactions.

• EarthquakescauselongitudinalwavescalledPwaves,whichpassthroughundergroundrocks.

Review

1. Whatisalongitudinalwave?2. Drawasketchofalongitudinalwave.Usearrowstoshowthedirectionofthewaveand

thedirectionofthevibratingparticlesofthemedium.Addlabelstoidentifythecompressionsandrarefactions.

3. DescribePwaves.