Here'sanotherexample.Thinkaboutawrench.Thecircleyoumakebypullingonthehandleisthewheel.Theaxleiswheretheheadofthewrenchgrabsabolt.Asmallerforceappliedtothehandlecanmovealargerloadattachedtothe axle.

Thesamekindofthinghappenswhenyouturnadoorknob.Theknobisawheelandisconnectedtoarod,whichistheaxle.Whenyouturntheknob,therodpullsonalatchthatmovesoutofthedoorframe.Now,youcanopenthe door.

Withsimplemachines,therearealwaystrade‑offs.Thelargerthewheel,thelessforceyouhavetouse.Butyouhavetousethatforceoveragreaterdistance.So,youtradedistanceforforce.That’snotabad trade!

Bikeshavemanywheelsandaxles—thewheelsandpedals,forexample.Bikesalsohavetoothedwheelscalledgears.Achainconnectsageararoundthepedalswithoneormoregearsontheback wheel.

Whenyoupedal,thechainturnstherearaxle.So,therearwheelturns,too.Thewheelismuchlargerthantheaxle.So,thewheelturnsfartherandfasterthantheaxle.Sodoesthefrontwheel.Itsortof“goesalongfortheride.”Wheelsandaxlesmakeworkeasier—andmore fun!