Problem

“Wow,lookatalltheseterrificbooks!”yousay,asyouskimoversomeofthetitlesinacardboard box.


“Yeah,”yourfriendsays,“buthowarewegoingtogetthemtothe library?”


It’sBookDonationDayatschool.Astrongstormsweptthroughtownlastmonth.Partofthelibrarywasdamaged.Noonegothurt,buttherainandwindruinedmanyofthebooks.Sostudents,teachers,andparentsorganizedabookdriveforthe library.


Whatasuccess!Peoplehavebeendroppingoffboxesofbooksallmorning.Heavyboxesofallsizesarestackedup,andadozenvolunteersarereadytocarrythemintothe library.


Theboxesaretooheavytopushordrag.Youandtheothervolunteerscouldleavetheboxesandjustcarryafewbooksatatime,butthatwouldtaketoolong.Therehastobeabetter way.

Solution

Youthinkforamoment.“I’vegotit!Comeon,wehavetogototheMaintenance Office.”


Fiveminuteslater,youandyourfriendcomewalkingdownthehallwaypullingtwodollycarts.Thevolunteersstacktheboxesonthedollies.Thentheyrolltheboxestothelibrary,unloadthem,andheadbackformore.Witheveryoneworkingtogether—andwiththerighttools—thejobisdoneinno time.

It's Simple

Whatmadethedolliessuchgoodtoolsformovingthebooks?It’ssimple!Thewheelsonthedollyarepartofasimplemachine.Simplemachineshelpusdoworkbymovingthingsfaster,farther,ormoreeasilythanwecanwithoutthe machine.

axle

wheel

axle

Simplemachineshavenomorethanafewparts.Somehavejustonepart.Nearlyeverymachineismadeupofoneormoresimple machines.


Thinkaboutaschoolbus.Thedoor’shingesarelevers.Thestairsareatypeofinclinedplane.Screwsholdseatframestothefloor.Andofcourse,thewheelsprovidethesmoothridetoandfrom school.

Youcanfindwheelsandaxlesonwagonsand bicycles.

MachinesThatGoRound

Awheelandaxleisasimplemachinethatturnsinacircle.Awheelisadiscthatturnsroundandround.Butwheelsdon’tworkbythemselves.Theyhave partners—axles!


Anaxleisarodconnectedtothecenterofawheel.Theaxleconnectsthewheeltoavehicle.Whentheaxlemoves,sodoesthewheel,andsodoesthe vehicle.

Imaginepullingaloadoflogsonawagonwithoutwheels.Thebottomwouldscrapeagainsttheground.Asyoupullforward,theforceoffrictionpullsintheoppositedirection.Wheelsroll.Thereislessfriction.So,ittakeslesseffortfromyoutopullthe wagon.