Unit 5 Energy - valentinesclass.weebly.com · • Thermal Energy – the total kinetic and...
Transcript of Unit 5 Energy - valentinesclass.weebly.com · • Thermal Energy – the total kinetic and...
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Unit5EnergyPHYSICALSCIENCEMRS. VALENTINE
5.1ThermalEnergyandHeatTransfer
• Objective:
• Iwillbeabletorecognizethesixformsofenergy.Iwillbeabletodistinguishbetweenheatandtemperature.Iwillunderstandthetypesofheattransfer.
• Vocabulary:
Energy Work Conduction Radiation AbsoluteZero
Convection NuclearEnergy ThermalEnergy Heat Temperature
ChemicalEnergy ElectricalEnergy ElectromagneticEnergy ThermalConductor ThermalInsulator
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5.1ThermalEnergyandHeatTransfer
• Energy• Theabilitytodowork.• Workisatransferofenergy.
• SIUnit:Joules(J)• 1J=1Nm=1kgm2/s2
5.1ThermalEnergyandHeatTransfer
• Therearesixmajorformsofenergy• MechanicalEnergy-associatedwiththemotionandpositionofeverydayobjects.• ChemicalEnergy–theenergystoredinchemicalbonds.• ElectricalEnergy–theenergyassociatedwithelectriccharges.• ElectromagneticEnergy–aformofenergythattravelsthroughspaceintheformofwaves.• NuclearEnergy–theenergystoredinatomicnuclei• ThermalEnergy–thetotalkineticandpotentialenergyofallthemicroscopicparticlesinanobject
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5.1ThermalEnergyandHeatTransfer
• ThermalEnergyandMatter• Thermalenergydependsonthemass,temperature,andphase(solid,liquid,orgas)ofanobject.
• DifferencebetweenHeatandTemperature• Heat• Thetransferofthermalenergyfromoneobjectbecauseofatemperaturedifference.• Heatflowsspontaneouslyfromhotobjectstocoldobjects.
5.1ThermalEnergyandHeatTransfer
• Temperature• Ameasureofhowhotorcoldanobjectiscomparedtoareferencepoint.• Absolutezeroisonesuchreferencepoint,equaling0Kelvin(-273°C)• Relatedtotheaveragekineticenergyoftheparticlesinanobjectduetotheirrandommotionsthroughspace.• Asanobjectheatsup,theparticlesmovefaster,onaverage.• Particlecollisionsfromtheincreasedmovementtransferthermalenergyfromhottocoldobjects.
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5.1ThermalEnergyandHeatTransfer
• ThermalExpansion• Theincreaseinvolumeofamaterialduetoatemperatureincrease.• Occursbecauseparticlesofmattertendtomovefartherapartastemperatureincreases.• Usedinglassthermometers.
5.1ThermalEnergyandHeatTransfer
• HeatTransfer• Heatistransferredfromonesubstancetoanotherviaoneofthreemethods.• Conduction• Thetransferofthermalenergywithnooveralltransferofmatter.• Occurswhenmaterialsaretouching.• Conductioningasesisslowerthaninliquidsandsolidsbecausetheparticlesinagascollidelessoften.
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5.1ThermalEnergyandHeatTransfer
• Conductorsandinsulators• ThermalConductors• Amaterialthatconductsthermalenergywell.• Ex:Metal,Tile• ThermalInsulators• Amaterialthatconductsthermalenergypoorly• Ex:Air,Rubber
5.1ThermalEnergyandHeatTransfer
• Convection• Thetransferofthermalenergywhenparticlesofafluidmovefromoneplacetoanother.• Aconvectioncurrentoccurswhenafluidcirculatesinaloopasitalternatelyheatsupandcoolsdown.• Ex:aircirculatinginanoven• Convectioncurrentsareimportantinmanynaturalcycles,suchasoceancurrents,weathersystems,andmovementsofhotrockinEarth’sinterior.
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5.1ThermalEnergyandHeatTransfer
• Radiation• Thetransferofenergybywavesmovingthroughspace.• Ex:heatlamps• Allobjectsradiateenergy.Asanobject’stemperatureincreases,therateatwhichitradiatesenergyincreases.
5.2LawofConservationofEnergy
• Objective:
• Iwillbeabletoidentifyandcalculatekineticandpotentialenergies.Iwillunderstandhowenergyisconservedandconvertedinvarioussituations.
• Vocabulary:
KineticEnergy PotentialEnergy ElasticPotentialEnergy EnergyConversion
LawofConservationofEnergy GravitationalPotentialEnergy
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5.2LawofConservationofEnergy
• KineticandPotentialEnergy• KineticEnergy• Theenergyofmotion.• Thekineticenergyofanymovingobjectdependsuponitsmassandspeed.• Equation&SIUnits• Equation:KE=(1/2)mv2
• SIUnit:Joules
5.2LawofConservationofEnergy
• Practice• A70.0-kilogrammaniswalkingataspeedof2.0m/s.whatishiskineticenergy?
• A1400-kilogramcarismovingataspeedof25m/s.Howmuchkineticenergydoesthecarhave?
• A50.0-kilogramcheetahhasakineticenergyof18000J.Howfastisthecheetahrunning?
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5.2LawofConservationofEnergy
• PotentialEnergy• Energythatisstoredasaresultofpositionorshape.• Types• GravitationalPotential• Potentialenergythatdependsuponanobject’sheight.• Increaseswithheight.• Anobject’sgravitationalpotentialenergydependsonitsmass,itsheight,andtheaccelerationduetogravity.• Anotherwaytosaythisistomultiplytheobject’sweightbyitsheight.• Equation:PE=mgh• Ex:amansittingonacliffedge
5.2LawofConservationofEnergy
• ElasticPotential• Potentialenergyofanobject’sthatisstretchedorcompressed.• Somethingissaidtobeelasticifitspringsbacktoitsoriginalshapeafteritisstretchedorcompressed.• Ex:astretchedhairbandoracompressedspring
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5.2LawofConservationofEnergy
• LawofConservationofEnergy• Energycanbeconvertedfromoneformtoanother.• Theprocessofchangingenergyfromoneformtoanotherisenergyconversion• Thelawofconservationofenergystatesthatenergycannotbecreatedordestroyed.• Inaclosedsystem(nothingcanenterorleave),theamountofenergyatthestartoaprocessisthesameamountofenergyattheend.
5.2LawofConservationofEnergy
• EnergyConversions• Thegravitationalpotentialenergyofanobjectisconvertedtothekineticenergyofmotionastheobjectfalls.
• Examples• RollerCoaster• Arollercoastergoesthroughaseriesofexchangesbetweenpotentialandkineticenergy.
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5.2LawofConservationofEnergy
5.2LawofConservationofEnergy
• Pendulums• Apendulumconsistsofaweightswingingbackandforthfromaropeorstring.• Kineticenergyandpotentialenergyundergoconstantconversionsinapendulumasitswings.• Atthehighestpoint,thependulummomentarilyismotionless,andhaszerokineticenergyandmaximumpotentialenergy.• Asthependulumswingsdownward,potentialenergyisconvertedbacktokineticenergy.• Atthebottomoftheswing,thependulumhaszeropotentialenergyandmaximumkineticenergy.• Unlessadditionalforceisaddedtothependulumcontinuously,thependulumwilleventuallystopbecauseoffrictionforces.
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5.2LawofConservationofEnergy
5.2LawofConservationofEnergy
• PoleVault• Whenthepole-vaulterspringsdowntherunway,hegainsasmuchkineticenergyashecan.Uponplantinghispole,someofthatkineticenergyisconvertedtoelasticpotentialenergyasthepolebends.• Thepolespringsbackintoshape,propellingthepole-vaulterupward,convertinghiskineticenergyintogravitationalpotentialenergy.• Oncethehighestpointhasbeenreached,hisgravitationalpotentialenergybeginstoconvertbacktokineticenergy.Thepole-vaulterpicksupspeedashefalls.
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5.2LawofConservationofEnergy
5.2LawofConservationofEnergy
• Equation:(KE+PE)beginning=(KE+PE)end• Practice• A10-kgrockisdroppedandhitsthegroundbelowataspeedof60m/s.Calculatethegravitationalpotentialenergyoftherockbeforeitwasdropped.Youcanignoretheeffectsoffriction.
• Adiverwithamassof70.0kgstandsmotionlessatthetopofa3.0-m-highdivingplatform.Calculatethepotentialenergyrelativetothewatersurfacewhilestandingontheplatform,andhisspeedwhenheentersthepool.
• Apendulumwitha1.0kgweightissetinmotionfromaposition0.04mabovethelowestpointonthepathofitsweight.Whatisthekineticenergyofthependulumatthelowestpoint?Assumethereisnofriction.
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5.3WorkandPower
• Objective:
• Iwillbeabletocalculateworkandpower.
• Vocabulary:
Work Power Horsepower Watt Joule
5.3WorkandPower
• Work• Inscience,workistheproductofforceanddistance.• Workisdonewhenaforceactsonanobjectinthedirectiontheobjectmoves.• Ex:applyingforceupwardtoliftaboxofftheground.
• Foraforcetodoworkonanobject,someoftheforcemustactinthesamedirectionastheobjectmoves.Ifthereisnomovement,noworkisdone.
• Aforcedoesnothavetoactentirelyinthedirectionofmovementtodowork,solongasaportionoftheforceisinthedirectionofthemovement.
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5.3WorkandPower
• Anypartofaforcethatdoesnotactinthedirectionofmotiondoesnoworkonanobject.
• Equation:work=F*d• SIUnit:Joules(J)
5.3WorkandPower
• Practice• Howmuchworkisdonetolifta1600Nbarbell2.0m?
• Amoverpushesa150Nboxupa6mincline.Howmuchworkdidthemoverdoonthebox?
• Ateacherleansonawallwithaforceof50N.Howmuchworkdidtheteacherdo?Explain.
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5.3WorkandPower
• Power• Poweristherateofdoingwork.• Doingworkatafasterraterequiresmorepower.Toincreasepower,youcanincreasetheamountofworkdoneinagiventime,oryoucandoagivenamountofworkinlesstime.
• Movingsnowtoclearadrivewayrequireswork.Whichonehasmorepower,shovelingbyhandorusingasnowblower?Why?
5.3WorkandPower
• Equation:power=work/time• SIUnit:Watt(W)• 1W=1J/s• Approximatelyequaltoliftingyourtextbookaheightofonemeterinhalfasecond.• Horsepower(hp)isanotherunitusedforpower.1hp=746watts.
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5.3WorkandPower
• Practice• Yourfamilyismovingtoanewapartment.Whileliftingabox1.5mstraightuptoputitonatruck,youexertanupwardforceof200Nfor1.0s.Howmuchpowerisrequiredtodothis.
• Youliftabookfromthefloortoabookshelf1.0mabovetheground.Howmuchpowerisusediftheupwardforceis15.0Nandyoudotheworkin2.0s?
• Youapplyahorizontalforceof10.0Ntopullawheeledsuitcaseataconstantspeedof0.5m/sacrossflatground.Howmuchpowerisused?
5.4WorkandMachines
• Objective:
• Iwillunderstandhowtorelateworkandmachines.Iwillbeabletodeterminehowamachinemakesworkeasieranditsefficiency.
• Vocabulary:
Machine InputDistance OutputForce InputForce WorkInput
OutputDistance WorkOutput MechanicalAdvantage Efficiency
IdealMechanicalAdvantage ActualMechanicalAdvantage
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5.4WorkandMachines
• MachinesDoWork• Amachineisadevicethatchangesaforce.• Machinesmakeworkeasiertodo.Theychangethesizeofaforceneeded,thedirectionofaforce,orthedistanceoverwhichaforceacts.• IncreasingForce• Whenusingamachine,asmallforceexertedoveralargerdistancebecomesalargerforceexertedoverasmallerdistance.• Ex:Turningasteeringwheelwithasmallerforceappliesalargerforcetothesmallersteeringcolumn.
5.4WorkandMachines
• IncreasingDistance• Amachinethatdecreasesthedistancethroughwhichyouexertaforceincreasestheamountofforcerequired.• Ex:Whenyouswingabaseballbat,yourhandsdonottravelasfarastheotherendofthebat.Youapplyalargerforcetothebatoverasmallerdistancewhilethebatappliesasmallerforcetotheballoveralargerdistance.
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5.4WorkandMachines
• ChangingDirection• Changingthedirectionofaforcecanmakeworkeasierwithoutchangingdistanceormagnitudeoftheforce.• Ex:Hoistingasail,youpulldownonaropetopullthesailup.
5.4WorkandMachines
• InputandOutputWork• Becauseoffriction,theworkdonebyamachineisalwayslessthantheworkdoneonthemachine.
• WorkInputtoaMachine • Theforceyouexertonamachineiscalledtheinputforce.• Thedistancetheinputforceactsthroughisknownastheinputdistance.• Theworkdonebytheinputforceactingthroughtheinputdistanceiscalledtheworkinput.• workinput=Finput*dinput
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5.4WorkandMachines
• WorkOutputofaMachine• Theforcethatisexertedbyamachineiscalledtheoutputforce.• Thedistancetheoutputforceisexertedthroughistheoutputdistance.• Theoutputworkofamachineistheoutputforcemultipliedbytheoutputdistance.• workoutput=Foutput*doutput
• Withoutachangetotheinputwork,theoutputworkwillremainthesame.
5.4WorkandMachines
• MechanicalAdvantage• Themechanicaladvantageofamachineisthenumberoftimesthanthemachineincreasesaninputforce.
• Forexample,ifanutcrackerexertsaforceseventimesgreaterthantheinput,thenitsmechanicaladvantageis7.
• Mechanicaladvantagedoesnothaveaunit.• ActualMechanicalAdvantage (AMA)• AMAequalstheratiooftheoutputforcetotheinputforce.• Equation:
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5.4WorkandMachines
• IdealMechanicalAdvantage(IMA)• IMAisthemaximummechanicaladvantagepossibleifthemachinewerefrictionless.• Becausefrictionisalwayspresent,theactualmechanicaladvantageofamachineisalwayslessthantheideamechanicaladvantage.• Equation:
5.4WorkandMachines
• Practice• Astudentworkinginagrocerystoreafterschoolpushesseveralgrocerycartstogetheralongaramp.Therampis3meterslongandrises0.5meters.Whatistheidealmechanicaladvantageoftheramp?• Aconstructionworkermovesacrowbarthroughadistanceof0.50mtoliftaload0.05moffoftheground.WhatistheIMAofthecrowbar?• TheIMAofasimplemachineis2.5.Iftheoutputdistanceofthemachineis1.0m,whatistheinputdistance?
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5.4WorkandMachines
• Efficiency• Thepercentageoftheworkinputthatbecomesworkoutputistheefficiencyofamachine.
• Becausethereisalwayssomefriction,theefficiencyofanymachineisalwayslessthan100%.
• Equation:
5.4WorkandMachines
• Practice• Youhavejustdesignedamachinethatuses1000Jofworkfromamotorforevery800Jofusefulworkthemachinesupplies.Whatistheefficiencyofyourmachine?
• Ifamachinehasanefficiencyof40%,andyoudo1000Jofworkonthemachine,whatwillbetheworkoutputofthemachine?
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5.5SimpleMachines
• Objective:
• Iwillbeabletoidentifyandcalculatethemechanicaladvantageforeachofthesixtypesofsimplemachines.Iwillunderstandwhatacompoundmachineis.
• Vocabulary:
Lever Fulcrum InputArm OutputArm WheelandAxle
InclinedPlane Wedge Screw Pulley CompoundMachine
5.5SimpleMachines
• Thesixtypesofsimplemachinesarethelevel,thewheelandaxle,theinclinedplane,thewedge,thescrew,andthepulley.
• SixTypes• Levers• Aleverisarigidbarthatisfreetomovearoundafixedpoint.• Thefixedpointthebarrotatesaroundiscalledthefulcrum.• Theinputarmofaleveristhedistancebetweentheinputforceandthefulcrum.• Theoutputarmisthedistancebetweentheoutputforceandthefulcrum.• Equation:
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5.5SimpleMachines
• ThreeClasses• 1stClass• Thefulcrumisinbetweentheinputandoutputforces.• Changesthedirectionoftheforceapplied.• IMAcanbe1,>1,or<1(dependingonlocationoffulcrum)• Examples:seesaw,scissors,tongs
5.5SimpleMachines
• 2ndClass• Theinputandoutputforcesareonthesamesideofthefulcrum;theoutputforceisclosertothefulcrum.• Outputforce>inputforce;outputarm>inputarm• IMA>1• Examples:wheelbarrow,bottleopener
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5.5SimpleMachines
• 3rdClass• Theinputandoutputforcesareonthesamesideofthefulcrum;theinputforceisclosertothefulcrum.• Outputforce<inputforce;outputarm<inputarm• IMA<1• Examples:baseballbat,rake,broom,hockeystick
5.5SimpleMachines
• Wheel&Axle• Awheelandaxleisasimplemachinethatconsistsoftwodisksorcylinders,eachonewithadifferentradius.• Dependingonthepurposeofthemachine,theinputforcecanbeexertedonthewheel(IMA>1)ortheaxle(IMA<1).• Examples:screwdriver,steeringwheel• Equation:
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5.5SimpleMachines
• InclinedPlanes• Aninclinedplaneisaslantedsurfacealongwhichaforcemovesanobjecttoadifferentelevation.• Examples:Wheelchairramp,boardingrampontoaship• Equation:
5.5SimpleMachines
• Wedge• AwedgeisaV-shapedobjectwhosesidesaretwoinclinedplanesslopedtowardeachother.• IMA>1• Athinwedgeofagivenlengthhasagreateridealmechanicaladvantagethanathickwedgeofthesamelength.• Examples:zipperteeth,knife,axehead
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5.5SimpleMachines
• Screw• Ascrewisaninclinedplanewrappedaroundacylinder.• Screwswiththreadsthatareclosertogetherhaveagreateridealmechanicaladvantage.• Thethreadonascrewisusuallymeasuredinthreadsperinchorthreadspercentimeter.• Examples:woodscrews,jarlids,nuts
5.5SimpleMachines
• Pulleys• Apulleyisasimplemachinethatconsistsofaropethatfitsintoagrooveinawheel.• Canchangemagnitude,distance,ordirectionofinputforce.• ThreeTypes
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5.5SimpleMachines
• FixedPulley• Awheelattachedinafixlocation.• Oftenabletorotateinplace.• Changesthedirectionoftheappliedforce,butnotthemagnitudeordistance.• IMA=1• Examples:flagpole,pulleyusedtopullupblinds
5.5SimpleMachines
• MovablePulley• Awheelattachedtotheobjectbeingmoved(theropeisattachedtoafixlocation).• Ifyouarepullingup,IMA=2• Examples:pulleysusedtohoistsails,skyscraperwindowwashersstandonplatformssuspendedbymovablepulleys.
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5.5SimpleMachines
• PulleySystem• Combinationsoffixedandmovablepulleys• CanachievehighIMA
• Equation:IMA=#ropesectionssupportingtheloadbeinglifted
5.5SimpleMachines
• CompoundMachines• Combinationoftwoormoresimplemachinesthatoperatetogether.
• Examples:systemofgears,acar,washingmachine