WheelsThatDon'tRoll

Notallwheelsandaxlesareusedforrollingthingsalong.Thinkaboutusingawrenchtotightenabolt,forinstance.Thecircleyoumakebypullingonthewrenchhandleisthewheel.Where’stheaxle?It’sattheotherend,wheretheheadofthewrenchgrabsthe bolt.


Youuseefforttoturnthewrenchhandlewithacertainamountofforce.Thecircleyoumake—thewheel—islargerthantheaxle.That’sthekey.Thelargerwheelincreasestheforceonthesmaller axle.

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Thesamekindofthinghappenswhenyouturnadoorknob.Theknobisawheelandisconnectedtoarod,whichistheaxle.Therodpullsonalatchthatmovesoutofthedoorframesothedoorcan open.


Theknobiseasytoturn.Thiswheelincreasesyourforceenoughtoturntheaxleandopenthedoor.Butthisamazingincreaseinforcecomeswithaprice,andthatpriceisdistance.Youturnthedoorknobalongerdistancethanyouwouldhavetoturnthe rod.


That’sthethingaboutsimplemachines:Therearealwaystradeoffs.Thelargerthewheel,thelessforceyouhavetoapply,butyouhavetoapplythatforceoveragreaterdistance.So,youtradedistanceforforce.Whenitcomestodoorknobsandwrenches,aswellasfaucetsandscrewdrivers,that’snotabad trade!

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WheelsandAxlesCanBeFun

HaveyoueverriddenonaFerriswheel?It’soneofthelargestwheelsandaxles.Amotorsuppliestheforcethatturnstheaxle.Theaxlemovesashortdistancebecauseitmakesasmallcircle.Thecarsattheouteredgeofthewheelmoveamuchlongerdistancebecausetheymakeamuchbiggercircle.Thebigcircleletstheridersclimbhighintothe air!

Unlikeadoorknob,aFerriswheeltradesforcefordistance.So,thiswheelandaxleincreasesthedistancethewheeltravels,nottheamountofforceneededtoturntheaxle.Thesameideaappliestoa merry‑go‑round.

AFerriswheelisnothingmorethanaHUGEwheeland axle!

GoingAlongfortheRide

Anotherfunwaytoenjoywheelsandaxlesisonabicycle.Abikeisloadedwiththiskindofsimplemachine.Ofcourse,thebigwheelswithtiresatthefrontandbackarewheelsandaxles.Soarethepedals.Theyareconnectedbyanaxleandformawheelastheyturn round.


Bikesalsohavetoothedwheelscalledgears.Achainconnectsageararoundthepedalswithoneormoregearsonthebackwheel.Whenyoupedal,thechainturnstherearaxle,sotherearwheelturns,too.Thewheelismuchlargerthantheaxle,sothewheelturnsalotfartherandfasterthantheaxle.Sodoesthefrontwheel,whichjust“goesalongforthe ride.”


Wheelsandaxlesmakeworkeasier—andmorefun!Whatotherwheelsandaxlescanyoufindaround you?

Differentkindsofwheelsandaxlesmakethisbike go.