Sec 2 G3 Chapter 9- application of forces and transfer of energy

CHAPTER9: ApplicationofforcesandtransferofenergyTYPESOfFORCES: 2.Non-contactforces-forcesexperiencedbybodieseveniftheyarenotinphysical1. Contactforces- forcesexperiencedbybodieswhentheyareinphysicalI /I contactwithcontactFrictional Tgravitationalmagneticelectrostatic eachotherapplied It↓ ~ forceface Forceexertedforceexertedforceofattractionbetweentwomassesbyachargebbyamagnetbodyonanotheri.e.thatattractsforcedueforcesactingopposite chargedbodyobjectstoEarthtotheaction ofMusclestothedirectionofmotion 3. friction- thecontactforcethatopposes/tendstoopposemotionbetweensurfacesincontact specialcases: 1. wheels 2,feetwalking*Notionofwheel *motionofobject *directionoffriction *directionoffriction1hM -> · tomovetotheright,thewheelshastorotateinaclockwisedirection· tomovetoright,thefoothastopushbackwardstotheground · frictionopposesmotion,thereforeitactstotheright ·frictionopposesmotion,thereforeitactstotheright Reducingnegativeeffectsoffriction wheels ballbearings directionof sphericalballbearingsworklikewheels.Theyrollaround,insteadofdraggingtheboxovertheground,motion thecircularshapeofthewheelsrotateandpreventsᶏ·allbearingsapevenmoving surfacesinmachinesfromrubbingagainst t beesdirectcontactwiththeground.Withlessfriction,one smallerforceisneededtomoveashoppingtrolley lubricant aircushion withlubricantadded,enginesurfacesincontactexperiencelessfrictionwhentheymoveagainstalayerofairbetweensurfacesreducesfriction,soahovercraftcantravelfaster eachother.Aroughsurfacegeneratesmorefrictioncomparedtothesmoothsurface Enhancingpositiveeffectsoffriction Treads->channelwateroutfromundertyres,whichimprovesthetyresgripontheroadsurface,andpreventsvehiclesfromskidding Farachute->thelargeairresistancecreatedbythecanopyofanopenparachuteslowsdownadescendingparachutist,sothathemaylandsafely Chalk->rockclimbersapplychalkpowdertotheirpalmstoabsorbsweet,andhenceimprovetheirgrip Comparingweightandmass weight Mass definition:themeasureofthegravitationalforceactingonanobject amountofmatterinanobject changes: canhavedifferentvaluesdependingongravitationalfieldstrength valueremainsunchanged,independentofgravitationalfieldstrength

SIunit: Newton(N) Kilogram(kg)instrumentto measure: springbalance electronicmassbalancebeambalance formulato(N)(kg)(n/kg) w (kg)(N)(N/kg)calculate: weight=massXgravitationalfieldstrength m9 mass=weight:gravitationalfieldstrength Gravitationalfield gravitationalfieldisaregioninwhichamassexperiencesagravitationalforceofattraction gravitationalfieldstrength,g,isthegravitationalforceactingperunitmass gravitationalfieldgetsstrongerastheobjectmovesclosertoearth onearth onMoon gravitationalfieldstrength,g:CON/kg 1.56N/kg -anobjectwithaMassof1kgwould ->anobjectwithamassoflkgwouldbe beattractedtowardsthecentreoftheearth attractedtowardsthecentreoftheEarthbya byaforceofION forceof1.66N TheforceofgravityontheMoonislessthanonEarth. AnyobjectwillweighlessonMoonthanonEarth.However,theobjectwouldhavethesamemassonMoon andEarth Whathappenswhentwoormoreobjectsinteract? forcesappliedonanobjectcancause:changesinthestateofrestormotionofanobject -musthaveapivot · changesduetotheturningeffectofaforceonanobject · changesinsize/shapeofanobject · changesinpressureonanobject transferofenergyduetoapplicationofforces changesinthestateofrestormotiononanobject whentwoormoreforcesareactingonanobject,theoverallforceactingontheobjectiscalledresultantforce ! 3-hSNy ↓ ·esuatu -surature·e - iftheresultantforceisON,theforcesareequal - iftheresultantforceis>ON,theforcesareunequalanditwillresultinaneffectontheobjects - aresultantforceisrepresentedbyadouble-headedarrow# ↓Whenthereisaresultantforce,energyistransferredbetweenobjects,whichmaycauseastationaryobjecttostarmoving · changethespeedofanobject(movefaster/slower · changethedirectioninwhichanobjectmoves · causeamovingobjecttostopmoving Changesduetotheturningeffectofaforceonanobject aforceappliedonanobjectcancauseaturningeffectaboutafixedpointcalledthepirot. Thisturningeffectiscalledthemomentofaforce. S.I. unitisNewton-metre(NmI.

Exampleofmomentsinourdailylife alargersteeringwheelenablesthedrivertoturnthe inordertoproducethesameturningeffect,moreforcetheseesawispivotedinthecentre.Inordertobalanceif steeringwheelmoreeasily;thisiswhylargebusesandheavyneedstobeappliedtomovetheoarsoveralongdistancecompletely,thesumofclockwisemomentmustbeequaltothesum sothatthecanoecanmovealungerdistancevehiclesnormallyhaslargersteelingwheels. ofanti-clockwisemoment calculatingmoments momentsofaforce=forcexperpendiculardistancefromthepivottothelineofactionoftheforce (NM)INM I momentofaforcehasadirection,eitherclockwiseoranti-clockwise whenanobjectisbalanced,thesumofclockwisemomentisequivalenttotheanti-clockwisemoment ·Changesinsize/shapeofanobject mouldingclayExamples:kneadingplasticine whenweapplyaforcetokneadplasticine,theshapeoftheplasticinechangesWhenwewouldalumpofwetclay,thesizeandshapeoftheclaychanges Changesinpressureofanobject pressureisaneffectofforceactingonanobjectandisdefinedastheamountofforceactingperunitarea Examples: weuseourfingerstoapplyforceontheheadofapin. Thespikesonthesolesoffootballshoeshaveasmallarea. Thecuttingedgesofknivesandscissorshaveverysmall Alargepressureiscreatedatthesharppoint.ThisallowsThelargepressureproducedbythespikesincreasestheshoesareas.Asmallforceproducesalargepressureonthecuttingedges. gripontheground.thepintopiercethroughpaperandwoodenboards. Thisallowstheedgestocutthroughobjectseasily- Stilettoheelsoftenleaveunsightlymarksincarpets.Thisis Whenwehammeranail,wemayaccidentallyhammerourfinger. Whenacartyrerollsoverthesharppointedendofanaily becausetheweightofthewearerexertsalargepressureona Thiscausesalargeforcetoactonasmallareaofourfinger. thenailexetsalargepressureonthetyreasthetipofthe smallareaofground. Thelargepressureonourfingerburststhebloodvesselsandproducesnailhasaverysmallarea.Thismaypuncturethetire. abruise. Calculatingpressure (pafora Pressureinliquids Thegreaterthedepth,thehigherthepressure.Thisisbecauseatagreaterdepth,thereisagreateramountofwateraboveaspecificpointascomparedtoapointthatisatashallowerdepth. Thegreateramountofwaterresultsinalargerweightofwaterabovethatpoint,henceforceexertedisgreater.

Examples: Buildingwatersupply Submarine -waterisdeliveredtoandstoredintanksatthetopofmosthighrisebuildingssubmarinesdiveverydeepunderwaterwherethereishighpressure - thiscauseswaterinpipesbelowthetankstobeatahigherpressureandensuresthatwaterastrongsubmarinebodyisneededtowithstandthehighpressure flowstotheunitsdown - submarineshaveadepthlimittoensurethatitkeepstoasafedepthwherethepressureisnothigh enoughtodamagethesubmarineorcauseanimplosion Atmosphericpressure - theearthissurroundedbyalayerofair(molecules)calledtheatmosphere - althoughwecannotseeorfeeltheairmolecules,theytakeupspaceandhaveweight - thus,theatmosphereexetsapressureontheEarth'ssurfaceandonus -thepressureexertedbytheairintheearth'satmosphereiscalledatmosphericpressure - atmosphericpressureisapproximately100,000Paatsealevel,anddecreasewithincreasingheightfromsealevel ExampleI-drinkingstraw Example2-suctioncup atmospheric wall- ↓suctioncup i ·-whenwesuckthroughastraw,wearereducingthepressureinthestraw = whenwepressasuctioncupagainstaflatsurface,airispushedoutfromunder -thiscausesapressuredifferencetobesetupbetweenthestrawandtheatmospherethecup - astheatmosphericpressureisgreater,itpushesonthesurfaceoftheliquid,forcing- thisreducestheairpressurebetweenthecupandthewall theliquidtoriseupthestrawintoourmouth -theatmosphericpressurearoundthesuctioncupishigherthaninsidethecup andhenceholdsitinplace Transferofenergycluetoapplicationofforces -energyistransferredwhenaforceappliedcausesanobjecttomoreinthesamedirectionastheforce - whenenergyistransferred,workisdonethroughapplicationoftheforce. - S1unitofenergyandworkdone:Joule(J) -conditionsforworkdone:1)aforceisappliedontheobject 2)objectmoves 3)objectmovesinthesamedirectionasforceapplied - workdonebyaconstantforceonanobjectistheproductoftheforceandthedistancemovedbytheobjectinthedirectionoftheforce (N)(m)- formula