Guitar String Lab - The Physics Classroom

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1 TheLaboratory GuitarStringLab TeachersGuide Topic: SoundandMusic Thefollowinginformationisprovidedtothestudent: Question: Howdoesdoubling,triplingandquadruplingthelengthofaguitarstringeffectthecollectionof harmonicfrequenciesatwhichitnaturallyvibratesandthespeedatwhichwavestravelwithinit? Purpose: Todeterminehowadoubling,triplingandquadruplingofthelengthofastringeffectsthecollectionof harmonicfrequenciesatwhichitnaturallyvibratesandthespeedatwhichwavestravelwithininit. AcompletelabwriteupincludesaTitle,aPurpose,aDatasection,aConclusionandaDiscussionof Results.TheDatasectionshouldincludetheprovidedtablewithalldatacollected.TheConclusion sectionshoulddescribetheeffectofdoubling,triplingandquadruplingthelengthuponthefrequency ofthewavesanduponthespeedofthewaves.TheDiscussionofResultssectionshouldprovidethe logicalsupportfortheconclusionstatementswhicharemade;specifictrialsshouldbereferencedas supportingevidence. MaterialsRequired: Digitalfunctiongenerator;wavedriver;wire;labpolesandclamps;pulley;500ghookedmass. DescriptionofProcedure: Anapproximately1.5meterlengthofsteelwireissecuredtoaclamponalabpoleatoneendofthelab table.A500ghookedmassissecuredtotheotherendofthewireanddrapedoverapulleyatthe oppositeendofthetable.Awavemachineissetupbyconnectingtheoutputofadigitalfunction generatortoawavedriver.Thewavedriverisattachedtothewireatadistanceof1.20mfromwhere thewireisattachedtothelabpole.Thefrequencyofthegeneratorisadjustedinordertoforcethewire tovibratewithitssecondharmonicpattern.Thefrequencyandharmonicnumberisrecorded.The frequencyisslowlyincreaseduntilthethirdandthefourthharmonicstandingwavepatternsare establishedinthewire.Thefrequenciesoftheseharmonicsarerecorded.Measurementsarecarefully repeatedforthesecond,thirdandfourthharmonicsforvibratingwirelengthsof0.90m,0.60m,and 0.30mfromthepole.Thedataarethenanalyzedinordertodeterminetheanswertothequestion raisedinthePurposeofthelab. AlternativeMaterialsandProcedure: Strongstringcanbeusedinplaceofsteelwire.Ifadigitalfunctiongeneratorandawavedriverarenot available,thenanonlineanimationcanbeusedtoaccomplishasimilarPurpose.Aneffectiveanimation forreplacingtheneedforadigitalfunctiongeneratorandawavedriverisfoundat: http://www.ngsir.netfirms.com/englishhtm/StatWave.htm SafetyConcern: Thereisalwaysahigherthanusuallevelofriskassociatedwithworkinginasciencelab.Teachers shouldbeawareofthisandtakethenecessaryprecautionstoinsurethattheworkingenvironmentisas ThePhysicsClassroom,2009

2 TheLaboratory safeaspossible.Studenthorseplayandofftaskbehaviorsshouldnotbetolerated.Studenthorseplay andofftaskbehaviorsshouldnotbetolerated.Studentswithlonghairshouldbecarefularounda vibratingwire.Entrapmentofthehairinthevibratingwireisacommonhazardandmostoftenresults inaverybadhairday. Suggestions,Precautions,Notes: 1. Thoughcostly,mechanicalwavedriversanddigitalfunctiongeneratorsareavailablefrommany sciencesupplyhouses.Forinstance,PascoScientificoffersthefollowingmodels:PI8127Function GeneratorandSF9324WaveDriver. 2. Dependingonthewirechosenforthislab,a500gmassmaynotbethebestmassforcreating tensioninthewire.Experimentwithvariousmassesinadvanceofthelab. 3. Warnstudentsaboutthehazardofdrapingtheirhairintothevibratingwireandbecoming entangled.There'smuchbetterwaystogetallwiredup. 4. Thislabwilltakeaperiodormoretomanipulateequipmentandtocollectreasonabledata.If studentshaveexperimentedwiththecreationofstandingwavepatternsinotherlabs,thenthislab couldserveasaneffectiveassessmentofstudents'abilityconductacontrolledinvestigationofthe effectandnoneffectofavariable(wirelength)uponotherquantities(frequencyandspeed).After explainingthePurposeclearly,itmightbewisetositback,stayoutofthestudents'wayand observetoseeiftheyhaveacquiredsuchaskill. AuxiliaryMaterials: ThefollowingpageisprovidedtothestudentforcompletionandinclusionintheDatasectionoftheir labnotebook. Harmonic Length Wavelength Frequency Speed Number (m) (m) (Hz) (m/s) 2 2 2 2 Harmonic Length Wavelength Frequency Speed Number (m) (m) (Hz) (m/s) 3 3 3 3 Harmonic Length Wavelength Frequency Speed Number (m) (m) (Hz) (m/s) 4 4 4 ThePhysicsClassroom,2009

3 TheLaboratory 4 Inthespacebelow,clearlyshowandlabelyourworkforthewavelengthand thespeedcalculationsforthetwotablesabove. ScoringRubric: S6. GuitarStringLab Score Included,labeledandorganizedallpartsofthelabreport. Datasectionincludesprovidedtable;tableiscomplete.Workfor calculationsareclearlyshownandlabeled.Dataisreasonablyaccurate. _____/_____ Conclusionclearlyandthoroughlydescribestheeffect(ornoneffect)that doubling,triplingandquadruplingthestringlengthhasuponthefrequency andthespeed.Writingisorganized,clearandrespondstothequestion.The conclusionsareaccurateandconsistentwiththedata. DiscussionofResultsprovidesthelogicalsupportfortheConclusion; specifictrialsofdataarecitedasevidenceinsupportofeachstatement madeintheConclusionsection. ConnectionstoThePhysicsClassroomTutorial: Thefollowingreadingsareasuitableaccompanimenttothislab: http://www.physicsclassroom.com/Class/sound/u11l4c.cfm http://www.physicsclassroom.com/Class/sound/u11l4d.cfm http://www.physicsclassroom.com/Class/sound/u11l5c.cfm ConnectionstoMindsonPhysicsInternetModules: Sublevels6an7oftheSoundandMusicmodulearesuitableaccompanimentstothislab: http://www.physicsclassroom.com/mop/module.cfm ThePhysicsClassroom,2009

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