Problem

Youarecampingwithyourfamilyandyourbestfriend.Afteradayoffuninthesun,youlookforwardtoanightnexttoabright,blazingcampfire.Especiallybecauseit’syourturntohelpstart it!


Youandyourfriendgathersomelogsandcrisscrosstheminasmallpile.Youraunttriestolightoneofthelogswithamatch.Nothinghappens.Shesmiles.“Thelogsaretoobigtocatchonfirewithsuchalittle flame.”


“Weneedsmallerpieces,” yousay.Buthow?Thewoodistoohardtobreakapartwithyourhands.“Weneedsomesortoftool,” yourfriendsays.“Maybesomeoneinthecampgroundhasasaw.”Allthatbackandforth sawing couldtakeawhile,youthink.Theremustbeabetter tool.

Solution

Thereis!Yourememberseeingasmallaxeinaboxofcampingequipment.It’stheperfecttoolforthe job!


Youbringittoyouraunt.Shestandsupalog andcarefullyswingstheaxesothatthebladestrikesthecutwoodontop.THWACK! The logsplitstoitshalfwaypoint.Anotherswing,andCRACK!Itsplitsin two.Afewmorewhacksreducethehalflogstopiecessmallenoughtostartthefire.Problem solved!

It's Simple

Whatmadetheaxesuchagoodtooltosplitwood?It’ssimple!Theaxeheadisasimplemachine.Likeallmachines,simplemachineshelpusdojobs,usuallybymovingthingsfaster,farther,ormoreeasilythanwecanwithoutthe machine.


Youprobablydon’tthinkofanaxeheadwhenyouhearthewordmachine.Instead,youmightpicturesomethingthatwhirsandpurrsor roars and rumbles.Ablender,acar,orabulldozermightcometomind.Theseareallcomplexmachineswithlotsof parts.


Simplemachines,ontheotherhand,haveonlyafewparts.Infact,somearemadeofonlyonepart.Nearlyeverymachine,nomatterhowcomplex,containsseveralsimple machines.

Thinkaboutawagon.Itstwosetsofwheelsandaxlesmakeiteasytotakeafriendforaride.Thehandleisalever.Itletsyoupullandsteerwithease.Andscrewsholdmanyofthewagonparts together.


Simplemachinescanbecombinedinendlesswaystoaccomplishtasks,fromsharpeningapenciltorocketingintospace.Buteachsimplemachinealsohelpsusdoworkallonits own.

force direction log axe head change in direction

AWedgeGivesYouanEdge

The axe head thatyouusedtosplitthewoodisasimplemachinecalledawedge.

It’sshapedlikeatriangle.Youmightnotnoticethisshapeatfirst.Infact,theaxeheadmightlookmorelikeasquare.Butlookdownatthetopofit.Doyouseehowtheheadstartsoutwideandthentaperstoathinedge?That’satriangle.Andhere’ssomethingtoremember:Thethinnertheedge,thesharperthe wedge.



Sohowdoesthiswedgedoitsjob?Itstartswitheffortfromyou.Ittakesefforttoswingtheaxe.Thiseffortprovidestheforceneededtodrivetheaxebladeintothe wood.


Whenyouswingtheaxeyoudirecttheforcedownward.Butasthebladepushesintothewood,thewedgedirectstheforcesideways.That’sthewholepointofawedge—itredirectsforce.Witheachdownwardswingoftheaxe,thewedgepushesoutwardin twodirections.Astheaxedrivesdeeper,thewoodmovesfartherandfartherapart,until,withonefinalCRACK, it splits.

WithapowerfulCHOP, thisaxehead ​​​​​​​splitsthewoodin two.Theaxeheadisawedge.

It’sAllAboutTrade-offs

Now,supposeyouhadtwoaxestochoosefrom.Onehasaheadthatislongandnarrow.Theotherhasaheadthatisshorterandwider.Whichwouldyou choose?


Remember,thethinnerthewedge,thesharpertheedge.So,thelong,narrowaxeheadwillbesharper.Choosingthisoneisano-brainer.Itwillbeeasiertodriveintothewoodwitheach swing.


Buthere’sthethingaboutasimplemachine:Therearealways trade-offs.

Thelong,narrowaxeiseasiertopushintothewood,butithastogodeeperbeforeitsplitsthelog.Theshort,wideaxecouldsplitthewoodwithoutgoinginsodeep.Thismightmeanfewerswings,buteachswingwouldrequirealotmoreforce,andalotmoreeffortfromyoutoprovidethat force.


So,youmayneedtotakeafewmoreswingstodrivethelong,narrowaxedeeperintothewood,butthey areeasyswings.Youtradedistanceforeffort.Notabad trade!