FanCart(ModifiedfromExploratorium’sTeacherInstitute)

Gradeλ(s):Upperelementarytomiddleschool Topic:Newton’sThirdLaw(andaspectsofforceandmotion)Standards:DisciplinaryCoreIdeas:PhysicalScience–ForcesandInteractionsForanypairofinteractingobjects,theforceexertedbythefirstobjectonthesecondobjectisequalinstrengthtotheforcethatthesecondobjectexertsonthefirst,butintheoppositedirection(Newton’sthirdlaw).(MS.PS2A.a)Themotionofanobjectisdeterminedbythesumoftheforcesactingonit;ifthetotalforceontheobjectisnotzero,itsmotionwillchange.Thegreaterthemassoftheobject,thegreatertheforceneededtoachievethesamechangeinmotion.Foranygivenobject,alargerforcecausesalargerchangeinmotion(acceleration)(MS.PS2A.b)ScienceandEngineeringPractices:AskingquestionsanddefiningproblemsPlanningandcarryingoutInvestigationsEngaginginargumentfromevidence Objective:LearnhowNewton’sThirdLawappliestodifferentconditions.

Materials: 2plasticdrinkingstraws SafetygogglesHot-gluegunandgluesticks 10x26cmprojectboard, Fourbeveledfaucetwashers(1/4L,19/32O.D.) FourCDsforwheels Two3/16woodendowels(14&16.5cmlong) One1/8-inchwoodendowel(about28cmlong)Styrofoamplate Woodblock(5x5xcm)Electricdrillandbits(1/8”and5/64”) Cablewithwithmountingheadforscrew(19cm)1.5-3.0VDChobbymotor Twowoodblocks(1x3x¾”&2x3x¾”)Atwo-blade6-inchplasticpropeller Phillipspan-headsheet-metalscrew(#8x¾”)

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Materials(continued)

Phillipsscrewdriver BatteryholderfortwoAAbatteriesTwoAAbatteries Sticky-backVelcro(about10inches)Ruler ScissorsOneminialligatorclip(optional) Needle-nosepliers(optionalforthealligatorclip)AdvancedPreparation:Cutstrawsto11.5cmand14.5cmlengths.Carefullyhotgluestrawstotheprojectboardabout2.5cm(or1inch)fromeachendthatwillactasbushingsforthewoodenaxles.Hot-gluecanandmaymelttheplasticstraws,soputtheglueontheposterboardinsteadofthestraws.Insertthewooden-dowelaxlesintothestrawsandcarefullyassemblethewashersandCDwheelsontothedowelaxles.Checktomakesurethewheelsturnfreelyinthestrawbushings.Drilla1/8-inchholeinthecenterofthe5x5cmsquarewoodblockforthemast-and-sailassembly.Insertthe1/8-indowelintothesquareblockforthemastandaddtheStyrofoamplateforthesail.(Optional:drawadesignonthesailwhilewaiting)Tightenthecabletiearoundthemotor.Cutofftheexcess.Usethe1/8drillbittodrillapilotholeforthesheet-metalscrew1-cmdownfromthetopofthe1x3x¾”block.Usecautionwhenyouhotgluethe1x3x¾”woodblocktothe2x3x¾”woodblockmakingsurethesheet-metalscrewholeisonthesideofthe1x3x¾”verticalwoodblockandnotfacingthefrontorbackside.Usecautionwhenyouhot-gluethebatteryholdertothe2x3x¾”horizontalwoodblock.WrapalongpieceofmaskingtapearoundeachAAbatterysothatyouhaveanextralengthoftapetogivesomethingtohelpremovingthebatteriesfromtheholder.Motorandpropellerassembly:Thecombinationofthemotorandpropellershapedetermineswhichdirectionthepropellerpushestheair.Ifairisbeingpushedbackwardswhenyouturnonthemotor,reversingtheconnections(wires)shouldreversethedirectionthemotorspinssothatthepropellerpushesairforwards.(Youcanalsotrytoreversethedirectionofthebatteries!).Optional:Ifyouhaveanon/offswitchthatyouwanttoattachtothecircuit(weareusingthealligatorclipandorpullingthebatteryoutasanon/offswitch),SeeSafetyPrecautionsonpage5forcorrectwaytoinstallswitch.λLIGOEducation2019 Exploremoreatwww.ligo.caltech.edu2

Activityλ:TodoandnoticeInvestigation1:Attachthesailtothecart,attachthefansoitblowsairtowardthebackofthecart

awayfromthesail.Beforeturningonthefan,predictwhatyouthinkwillhappenandthenobservewhathappens.

Investigation2: Adjustthefansothatitisattachedtothecartbutblowsairtowardsthefrontofthe

cart(wherethesailis).Removethesailassembly(orpullthesailallthewayupsowhenyouturnonthefan,theairisnotblowingonthesail.Makeyourpredictionbeforeyouturnonthefanandobservewhathappens!

Investigation3: Replacethesailbackontothecart(ormovethesaildownthewoodendowel)and

thistimeremovethefanassemblyfromthecart,andholditinyourhandwhileitblowsairtoward/ontothesail.Makeyourpredictionandobservewhathappens.

Investigation4: Attachthefanassemblybackontothecartsothatitblowsairtoward/ontothesail.

Predictwhatwillhappenbeforeyouturnonthefanandobservewhathappens.Investigation5: SimilartoInvestigation#4,withthefanandsailbothattachedtothecartandthe

fanblowingairtowardsthesail.Holdafilefolder(orastiffpieceofpaper)betweenthefanandthesail(butnottouchingeitherone!)andobservewhathappens.

UnderlyingScience:Hereisasummaryoftheresultstobeexpectedfortheinvestigationsabove:

1. Cartmovesforwards. 2. Cartmovesbackwards.3. Cartmovesforwards4. CartdoesNOTmove!(Youdidnothingwronghere…)5. Initiallythecartdoesn’tmove,butwhenthefilefolder(orstiffpieceofpaper)isinplace,the

cartmovesbackwards!

ThebehaviorofthecartisaclassicexampleofNewton’sThirdLaw:

Foreveryaction,thereisanequalandoppositereaction.

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MoreExplanationsInvestigation1:Byphysicallyreversingthefan,thefanpushestheairbackwardandairpushesthe

fanforward.Sincethefanisattachedtothecart,thecartmovesforward.Investigation2:Thefanpushestheairforwardsandtheairpushesthefanbackward.Sincethefan

isattachedtothecart,thecartispushedbackward.Investigation3:Thefanpushestheairforwardandtheairpushesthefanbackward.Butthefanisin

yourhandandnotattachedtothecart,thereisnoeffectonthecartforthisaction-reactionpair.Theairpushesthesailforwardandthesailpushestheairbackward.Sinceonlythesailisattachedtothecart,thecartmovesforward.

Investigation4:Thefanpushestheairforwardandtheairpushesthefanbackward.(Acrucialthing

tokeepinmindisthatactionandreactionforces,oftencalledanaction-reactionpair,donotactonthesameobject.)Ifthiswasallthatwashappening,thecartwouldmovebackward:Thefanisbeingpushedbackward,andsinceitisattachedtothecart,thecartisalsopushedbackward.Thesailissetinplace,sothereisasecondaction-reactionpair,withtheairpushingforwardonthesailandthesailpushingbackwardontheair.Inthissituation,therearetwoforcesexertedonthecart:airpushingbackwardonthefan,andairpushingforwardonthesail.Thesetwoforcesbalanceeachother,andthecartdoesNOTmove!

Investigation5:Initially,thecartisinthesameconfigurationasinInvestigation4,soitdoesn’t

move.However,whenabarrierisinsertedbetweenthefanandthesail(withouttouchingeitherone),thenthefirstaction-reactionpairisthesameasinInvestigation1:Thefanpushestheairforward,andtheairpushesthefanbackward.Inthesecondaction-reactionpair,theairpushesthefilefolderforward,andthefilefolderpushestheairbackward.Buttheonlyforceinthetworeactionpairsthatactsonthecartitselfistheforceonthefan,whichisconnectedtothecart,sothecartmovesbackward.

Furtherchallenges:Whatdoyouthinkwouldhappenifthesailwasmovedpartwayup,sothatthe

fanwasonlyblowingontohalfthesail,aquarterofthesail,¾ofthesail? Tryusinga3-inchdouble-bladepropeller,oratriple-bladepropeller. ___________________________________________________________________________________λLIGOEducation2019 Exploremoreatwww.ligo.caltech.edu4

LIGOConnection:LIGO’sinterferometerisverysensitivetoenvironmentalconditions.Everytime acarpushesonthegrounditacceleratestheground,whichacceleratespartsof

LIGO,causingthingslikethemirrorsinLIGOtostartaccelerating.That’swhyLIGOusesseismicisolationsystemsinordertokeeptheseforcesfromgettingtotheinterferometerparts(suchasthemirrors).Thereisevenanaction/reactionpairwiththelight!Whenthelightreflectsoffoftheendmirror,itactuallypushestheendmirrortheoppositedirection-justlikeaballhittingapendulum!

Resources:https://www.exploratorium.edu/snacks/fan-cartSafetyConsiderations: Usecautionwhenworkingwithhot-glueguns(especiallytheveryhigh-

temperatureguns!) Usesafetyglasseswhenworkingwithhand-drills. Avoidanyshort-circuitsbywrappingelectricaltape(oruseshrinkwrap)

aroundexposedwireconnections.

*Diagramforinsertingaswitchcorrectlytopreventashort-circuit! λLIGOEducation2019 Exploremoreatwww.ligo.caltech.edu5

‘Harder-to-find’materialslist(Innoparticularorder)

Cable-ties BeveledWashers AlligatorClips Metalscrews

1x1inchsquaredowels(Lowe’s)

MaterialsboughtoffofAmazonoreBay

1.5vmotors,AAbatteryholdersandon/offswitches 6-inchdouble-bladepropellers

Smallprint:EUDAX15setRectangularDCMotorMiniElectricMotor1.5-3V24,000RPMwith9.8”leadwires with2x1.5VAAbatteryholdercase.

Optional:3-inchminiCDsλLIGOEducation2019 Exploremoreatwww.ligo.caltech.edu6