Notallwheelsandaxlesareusedforrolling.Thinkaboutawrench.Thecircleyoumakebypullingonthehandleisthewheel.Theaxleiswheretheheadofthewrenchgrabsthe bolt.

Youuseefforttoturnthewrenchhandlewithforce.Thekeyisthatthecircleyoumakeislargerthantheaxle.Thisincreasesthe force.

Thesamethinghappenswhenyouturnadoorknob.Theknobisawheelconnectedtoarod—theaxle.Therodpullsonalatchthatmovesoutofthedoorframe.Nowthedoorcan open.

Thisincreaseinforcecomeswithaprice,andthatpriceisdistance.Youturnthedoorknobalongerdistancethantherod turns.

That’sthethingaboutsimplemachines:Therearealwaystrade‑offs.Thelargerthewheel,thelessforceyouhavetoapply.Butyouhavetoapplythatforceoveragreater distance.

So,youtradedistanceforforce.Whenitcomestodoorknobsandwrenches,aswellasfaucetsandscrewdrivers,that’snotabad trade!

Anotherfunwaytoenjoywheelsandaxlesisonabicycle.Abikeisloadedwithwheelsandaxles.Thewheelsandpedalsare examples.

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

Wheelsandaxlesmakeworkeasier—andmorefun!Whatotherwheelsandaxlesdoyouuseeach day?