Problem
Youclimbthelastfewrungsoftheladderandstepinside.“Wow,isthiscool!”Yourfriendisrightbehindyou.“Itoldyou so.”
It’syourfirsttimeinyourfriend’streehouse, andwhatasweetsetup.Ithasjustabouteverythingyoucouldwantinabackyardhideaway—twocomfychairs,atable,abookshelf,games,evena TV.
Youplopdowninachairandlookaround.Thenyourealizesomething.“I’mhungry.Gotanyfooduphere?”“Oh,IknewIforgotsomething,”yourfriend says.
Justthen,yourfriend’sgrandmothercomesoutofthehousecarryingtwolunch bags.
“Yay,Grandma,youreadourminds!Now,ifonlytherewasawaytogetthebagsup here.”
“Hmm . . .”Grandmastaresatathickbranchnearthedoorwayofthetreehouse.“Ihaveanidea.I’llberight back.”
Solution
Afewminuteslater,Grandmacomesbackwitharopeandabucket.“What’sthatfor?”yourfriendasks.“You’llsee,”Grandmasaysasshetiesabigknotinoneendofthe rope.
Sheswingstheknottedendafewtimesandletsitfly.Theropesailsoverthebranch.Theknotdanglesjustafewfeetabovetheground.Grandmaundoestheknotandtiestheendtothebucket handle.
“Oh,Igetit!”yousay.“Whatagreatidea!”Grandmaplacesthelunchbagsinthebucketandpullstheotherendoftherope.Witheachpull,thebucketrisesclosertothetreehousedoor.Atthetop,it’seasytoreachoutandgrabthebucket. . . andlunch.Now,thetreehouseisperfect.Itevenhasafooddelivery system!
It's Simple
HowwasGrandmaabletodeliverfoodtoyouandyourfriendwithoutclimbingtheladder?Theansweris“simple.”Sheusedtheropeandthebranchasasimplemachine.Likeallmachines,simplemachineshelpusdojobs,usuallybymovingthingsfaster,farther,ormoreeasilythanwecanwithoutthe machine.
Simplemachineshavenomorethanafewparts.Infact,somearemadeofonlyonepart.Theycanbecombinedinendlesswaystoaccomplishtasks.Buthowcanaropeandabranchbea machine?
IntheGroove
Well,basedontheheadlineofthisarticle,youprobablyknowtheropeandbranchformedapulley.Apulleyisawheelwithacordwrappedaroundit.Thecordmightbeastring,arope,achain,orevenasteelcable.Usuallythecordfitsinagroovearoundtherimofthewheel.Thatway,thecorddoesn’tslipout.Thewheelturnsfreelyasthecordispulledthroughthe groove.
Thebranchdoesn’thaveagroove,anditcertainlydoesn’tturnlikeawheel,buttheideaisthesame.WhenGrandmapulleddownononeendoftherope,theotherend,withthebucketattached,movedup.That’sonewayapulleymakesiteasiertoliftobjects.Itchangesthedirectionofa force.
Aflagpoleworksthesameway.Aropeisloopedthroughapulleyatthetopofthepole.Toraisetheflag,youattachittoonesideoftheropeandpulldownontheotherside.Theflaggoes up!
Likeanysimplemachine,apulleydoesn’tdotheworkforyou.Toraisetheflag,youhavetopullwithacertainamountofforce.Thepulleydoesn’tincreaseyourforce.Itjustchangesitsdirection.Butthat’saloteasierthanclimbingupthepole,tyingtheflagatthetop,andthenslidingdownagain.Safer, too!
Howtoraiseaflagwithapulley
1
Pulldownonthisendofthe rope.
2
Theropemovesthroughthe pulley.
3
Theflagmovesupwiththisendofthe rope.
