Problem

You arecampingwithyourfamilyandyourbestfriend.Afteradayoffuninthesun,youlookforwardtoanightnexttoabright,blazingcampfire.Especiallybecauseit’syourturntohelpstart it!


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


“Weneedsmallerpieces,”yousay.Buthow?Thewoodistoohardtobreakapartwithyourhands.“Weneedsomesortoftool,”yourfriendsays.“Maybesomeoneinthecampgroundhasasaw.”Allthatbackandforthsawingcouldtakeawhile,youthink.Theremustbeabetter tool.

Solution

Thereis!Yourememberseeingasmallaxeinaboxofcampingequipment.It’stheperfecttoolforthe job!


Youbringittoyouraunt.Shestandsalogupandcarefullyswingstheaxesothatthebladestrikesthecutwoodontop.THWACK!Thelogsplitstoitshalfwaypoint.Anotherswing,and CRACK!It splitsin two.Afewmorewhacksreducethehalflogstopiecessmallenoughtostartthe fire.


Problem solved!

It'sSimple

Whatmakestheaxeagoodtooltosplitwood?It’ssimple!Theaxeheadisasimplemachine.Likeallmachines,simplemachineshelpusdojobs,usuallybymovingthingsfaster,farther,ormoreeasilythanwecanwithout them.


Youprobablydon’tthinkofanaxeheadwhenyouhearthewordmachine.Ablender,acar,orabulldozermightcometomind.Buttheseareallcomplexmachines.Theyhavelotsof parts.

Simplemachineshaveonlyafewparts.Infact,some aremadeofonlyonepart.Nearlyeverymachine,nomatterhowcomplex,containsoneormoresimple machines.


Simplemachinescanbecombinedinendlesswaystocompletetasks,frompullingaloadtoflyinginspace.Buteachhelpsusdoworkallonits own.

Force direction. log. Axe head. Change in direction.

AWedgeGivesYouanEdge

Theaxeheadthatyouusedtosplitthewoodisasimplemachinecalledawedge.It’sshapedlikeatriangle.Atfirst,itmightlooklikeasquare.Butlookdownatthetopofit.Theheadstartsoutwideandthennarrowstoathinedge.Thethinnertheedge,thesharperthe wedge.


Howdoesitwork?Itstartswith effort fromyou.Ittakesefforttoswingtheaxe.Thiseffortprovidesthe force todrivetheaxeintothe wood.


Asyouswingtheaxe,theforcemovesdownward.Butastheaxepushesintothewood,thewedge shapedirectsthatforcesideways.Awedgeredirectsforce.Astheaxedrivesdeeper,thewoodmovesfartherandfartherapart,until,withonefinalCRACK, it splits.

WithapowerfulCHOP, thisaxesplitsthewoodin two.Theaxeheadisawedge.

It’sAllAboutTrade-offs

Now, supposeyouhadtwoaxestochoosefrom.Onehasaheadthatislongandnarrow.Theotherisshorterandwider.Whichwouldyou choose?


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

Buthere’sthethingaboutasimplemachine:Therearealwaystrade-offs.Thelong,narrowaxeiseasiertopushintothewood,butithastogodeeperbeforeitsplitsthelog.Theshort,wideaxecouldsplitthewoodwithoutgoinginsodeep.Thismightmeanfewerswings,buteachswingwouldrequirealotmoreforce.Youtradedistanceforeffort.Notabad trade!