Tony Ford Science Monday, 1 December 2014 Page 1
8.3Lesson2PrinciplesofSimpleMachines
Fromtheinventionofthewheelandprobablybeforethatmanhasbeenutilising
machinesortoolsthathelphim/hertomakelifeeasierandreduceeffortwhen
doingwork.(RememberfromLesson1Workisdonewhenenergyisusedupand
objectsmoveorchange.)
Imaginetryingtopushawheelbarrowuphillwithoutwheels?Imaginetryingto
liftthatwheelbarrowwithouthandles?Wheelsandhandlesorleversare
examplesofsimplemachinesthathelptodowork.
Othersimplemachinesincludeaxles,gears,pulleys,inclinedplanesandscrews.
Theyarecalledsimplebecausetheycontainonlyonemachinetype.Ifyoulookat
morecomplexmachineslikewheelbarrows,bicycles,clocksandcranesetc.you
willseemanyofthesesimplemachinesusedtogethertoassistwithdoingwork.
Purposeofmachines:
Mustdoatleastoneof:
1. Toreduceeffortforce
2. Toincreasedistanceorspeed
3. Tochangedirection
Examples
1. Ifyouusealonghandledsocketspanner
(wrench)toundotightnutsonacarwheel,
thelongerthehandletheeasieritisbecausethisisa
machinethatreducesforce.
2. IfyouuseaHishingrodthatbendsandtheotherendof
therodpropelsthetackle(hook,line,baitandsinker),
asyouHlickyourend,thelongertherodthefurtherthe
tacklewillgobecausethisisamachinethatincreases
distance.
3. Ifyouhangapulleywitharopeonabeamandtie
oneendtoaweight.Youcanlifttheweightvery
highbecauseyoucanpulldownonalongrope
ratherthantryingtopushitup.Thisisamachine
thatchangesdirection.
Tony Ford Science Monday, 1 December 2014 Page 2
1. Levers
Leversarejustsolidobjectslike
planksandcrowbarsthatcan
transferaforcefromoneplaceto
another.
•
Aleverallowsapplicationofinput
forceoreffort3atadistance
fromtheoutputforce1.
•
•
•
Afulcrumorpivot2iswherethe
leversitsandallowsfreerotation
motion.
Thefurtherawaytheapplication
offorceisfromthepivot,thelessinputforceisneededforaheavyload.
Thefurtherawaytheloadisfromthepivotthefurtheritwilltravel.
Q.Howwouldyouchangetheabovediagramforacatapult?
TypesofLevers
1. CLASS1(Pivotinthemiddle)
F out
Twotypes:
A. IfdIN>dOUTInputForce<Output
Force
dOUT
B. ifdIN<dOUTInputforce>Outputforce
dIN
F in
F in
2. CLASS2(Pivotontheend)
(dIN>dOUT)InputForce<Outputforce
F out
dIN
dOUT
F out
F in
3. CLASS3(Pivotontheend)
(dIN<dOUT)InputForce>Outputforce
dIN
dOUT
Tony Ford Science Monday, 1 December 2014 Page 3
Theseleversthencanbea:
1. Forceadvantage(inputforceislessthanoutputforcesolesseffortis
needed)
2. Distanceadvantage(inputforceisgreaterthanoutputforcesomore
effortisneededbuttheloadgoesfurtherorfaster)
Q1.UsingtheLeverClassesonpreviouspage,categorisetheclassesbelowinto
theiradvantagetype(ForceorDistance):
Lever
Examples
Advantage
CLASS1A
Crowbarprizinguparock.
Clawhammerremovinganail.
CuttingwithScissors
Grippingwithpliers
CLASS1B
UsingaCatapult
CLASS2
LiftingaWheelbarrow
Usingastapler
Usinganutcracker
Rowingaboat
CLASS3
CastingaFishingrod
Usingtheforearmtoliftarock
UsingBBQtongs
Q2.Inthediagramsbelow;drawintheinputforceFIN,outputforceFOUTand
Pivot
.
Tony Ford Science Monday, 1 December 2014 Page 4
2.Pulleys
Apulleysystemusesatleastonewheelandaropethattransferstheforcefrom
onesideofthewheeltotheother.
Singlepulleyschangedirectionoftheforcebuthavenoforceordistance
advantage.Theloadmovesthesamedistanceandrequiresthesameforcetolift
it,butforawkwardheightsorpositionsthesinglepulleyisstilluseful.
Multiplepulleysystemsaremoreuseful,notonlyprovidingchangeindirectionif
neededbutalsoaforceadvantage.
Theforceadvantageisduetothenumberofropesectionsliftingtheweight.The
morepulleysandropesthegreatertheadvantage:
“BlockandTackles”havetwoHixedpulleys(atthetop)andtwo
moveablepulleysthatrisewiththeload.
Theadvantageisthemuchsmallerforcerequiredtolifttheload.
Thedisadvantageisthelargedistanceneededtopulltherope,fora
smallriseoftheload.
Inthediagramsshownbelow,eachropesectionhalvestheforce.
TheEffortorinputforceis¼oftheloadoroutputforcefora4
pulleysystem.
Inrealpulleysystemsthough,morethan¼forceisneededbecause
offrictionbetweentheropeandpulleys.
Tony Ford Science Monday, 1 December 2014 Page 5
Q.InthediagramsbelowlabeltheinputandoutputforcesandlabeltheHixedand
moveablepulleys.
BlockandTackleSystem-
expandeddiagram
BlockandTackleSystem
3.WheelandAxles
Wheelsandaxlesaresimilarto:
1. ASecondClasslever.Thepivotisinthemiddle.Effortonthewheeland
loadisontheaxle.ExampleSteeringwheels,bicyclehandlebar,tapsand
doorhandles.TheWheelsconnectedtoaxlesturnasmallforceonthe
wheelintoalargeforceontheaxle.Thebiggerthewheel,the
easiertheforcerequiredtoturnthe
axle.
Wheel
axle
axle
Wheel
axle
Wheel
Tony Ford Science Monday, 1 December 2014 Page 6
2. AThirdClasslever.Thepivotisinthemiddle.Effortontheaxleandloadis
onthewheel.Examplewheelsofbicycles,carsetc.Theaxleconnectedto
thewheelturnsasmalldistanceandthewheelontheedgeturnsamuch
largerdistance,increasingthespeed.Thebiggerthewheel,thefasterit
willgo.
TrainEngineturningaxle Cyclistturningpedalstoturnaxleofwheel
Loadon
wheel
Effort
Effort
Onaxle
Loadon
wheel
Q1.Theoutsideofthewheelofacarmovesfurtherthanthe
axleforeachrotationsowhichonewhichoneisfaster?
DI
FI
Q2.UsethediagramshowingFIandFOforcesandtheDIandDO
circumferencestoexplainit.
DO
FO
4.InclinedPlanes
Effort
Ramps,steps,wedges,axeheads,chiselsand
screwsareallexamplesofaninclinedplane,
whichisjustaslopededgeortable.
Theforceadvantageoccursbecauseyouhaveto
pushforalongdistance.
Load
Thelesstheangleoftherampthelesstheforceisneededbutyouneedalonger
ramp.
•
AWedge(knife,chisel,axehead)isasingleordouble
inclinedplane,Whenyoupushitintoamaterial,it
Tony Ford Science Monday, 1 December 2014 Page 7
goesuparampmakingiteasier.
• Ascrewisaspiralramp,whenyoutwistitintoa
material,thematerialispulleduptheramp.
Q.Howcouldyouincreasetheforceadvantageof
wedgesandscrews?
DoInvestigation:8.4Analysingamachine