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

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

Thesamekindofthinghappenswhenyouturnadoorknob.Theknobisawheelandisconnectedtoarod,whichistheaxle.Therodpullsonalatchthatmovesoutofthedoorframesothedoorcan open.

Theknobiseasytoturn.Thiswheelincreasesyourforceenoughtoturntheaxleandopenthedoor.Butthisamazingincreaseinforcecomeswithaprice,andthatpriceisdistance.Youturnthedoorknobalongerdistancethanyouwouldhavetoturnthe rod.

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

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

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

Wheelsandaxlesmakeworkeasier—andmorefun!Whatotherwheelsandaxlescanyoufindaround you?