Unit 5 Energy - valentinesclass.weebly.com · • Thermal Energy – the total kinetic and...

11/29/17

1

Unit5EnergyPHYSICALSCIENCEMRS. VALENTINE

5.1ThermalEnergyandHeatTransfer

•  Objective:

•  Iwillbeabletorecognizethesixformsofenergy.Iwillbeabletodistinguishbetweenheatandtemperature.Iwillunderstandthetypesofheattransfer.

•  Vocabulary:

Energy Work Conduction Radiation AbsoluteZero

Convection NuclearEnergy ThermalEnergy Heat Temperature

ChemicalEnergy ElectricalEnergy ElectromagneticEnergy ThermalConductor ThermalInsulator

11/29/17

2

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

11/29/17

3

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.

11/29/17

4

5.1ThermalEnergyandHeatTransfer

• ThermalExpansion• Theincreaseinvolumeofamaterialduetoatemperatureincrease.• Occursbecauseparticlesofmattertendtomovefartherapartastemperatureincreases.• Usedinglassthermometers.

5.1ThermalEnergyandHeatTransfer

• HeatTransfer• Heatistransferredfromonesubstancetoanotherviaoneofthreemethods.• Conduction• Thetransferofthermalenergywithnooveralltransferofmatter.• Occurswhenmaterialsaretouching.• Conductioningasesisslowerthaninliquidsandsolidsbecausetheparticlesinagascollidelessoften.

11/29/17

5

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.

11/29/17

6

5.1ThermalEnergyandHeatTransfer

• Radiation• Thetransferofenergybywavesmovingthroughspace.• Ex:heatlamps• Allobjectsradiateenergy.Asanobject’stemperatureincreases,therateatwhichitradiatesenergyincreases.

5.2LawofConservationofEnergy

•  Objective:

•  Iwillbeabletoidentifyandcalculatekineticandpotentialenergies.Iwillunderstandhowenergyisconservedandconvertedinvarioussituations.

•  Vocabulary:

KineticEnergy PotentialEnergy ElasticPotentialEnergy EnergyConversion

LawofConservationofEnergy GravitationalPotentialEnergy

11/29/17

7

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?

11/29/17

8

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

11/29/17

9

5.2LawofConservationofEnergy

• LawofConservationofEnergy• Energycanbeconvertedfromoneformtoanother.• Theprocessofchangingenergyfromoneformtoanotherisenergyconversion• Thelawofconservationofenergystatesthatenergycannotbecreatedordestroyed.•  Inaclosedsystem(nothingcanenterorleave),theamountofenergyatthestartoaprocessisthesameamountofenergyattheend.

5.2LawofConservationofEnergy

• EnergyConversions• Thegravitationalpotentialenergyofanobjectisconvertedtothekineticenergyofmotionastheobjectfalls.

• Examples• RollerCoaster• Arollercoastergoesthroughaseriesofexchangesbetweenpotentialandkineticenergy.

11/29/17

10

5.2LawofConservationofEnergy

5.2LawofConservationofEnergy

• Pendulums• Apendulumconsistsofaweightswingingbackandforthfromaropeorstring.• Kineticenergyandpotentialenergyundergoconstantconversionsinapendulumasitswings.• Atthehighestpoint,thependulummomentarilyismotionless,andhaszerokineticenergyandmaximumpotentialenergy.• Asthependulumswingsdownward,potentialenergyisconvertedbacktokineticenergy.• Atthebottomoftheswing,thependulumhaszeropotentialenergyandmaximumkineticenergy.• Unlessadditionalforceisaddedtothependulumcontinuously,thependulumwilleventuallystopbecauseoffrictionforces.

11/29/17

11

5.2LawofConservationofEnergy

5.2LawofConservationofEnergy

• PoleVault• Whenthepole-vaulterspringsdowntherunway,hegainsasmuchkineticenergyashecan.Uponplantinghispole,someofthatkineticenergyisconvertedtoelasticpotentialenergyasthepolebends.• Thepolespringsbackintoshape,propellingthepole-vaulterupward,convertinghiskineticenergyintogravitationalpotentialenergy.• Oncethehighestpointhasbeenreached,hisgravitationalpotentialenergybeginstoconvertbacktokineticenergy.Thepole-vaulterpicksupspeedashefalls.

11/29/17

12

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.

11/29/17

13

5.3WorkandPower

•  Objective:

•  Iwillbeabletocalculateworkandpower.

•  Vocabulary:

Work Power Horsepower Watt Joule

5.3WorkandPower

• Work•  Inscience,workistheproductofforceanddistance.• Workisdonewhenaforceactsonanobjectinthedirectiontheobjectmoves.• Ex:applyingforceupwardtoliftaboxofftheground.

• Foraforcetodoworkonanobject,someoftheforcemustactinthesamedirectionastheobjectmoves.Ifthereisnomovement,noworkisdone.

• Aforcedoesnothavetoactentirelyinthedirectionofmovementtodowork,solongasaportionoftheforceisinthedirectionofthemovement.

11/29/17

14

5.3WorkandPower

• Anypartofaforcethatdoesnotactinthedirectionofmotiondoesnoworkonanobject.

• Equation:work=F*d• SIUnit:Joules(J)

5.3WorkandPower

• Practice• Howmuchworkisdonetolifta1600Nbarbell2.0m?

•  Amoverpushesa150Nboxupa6mincline.Howmuchworkdidthemoverdoonthebox?

• Ateacherleansonawallwithaforceof50N.Howmuchworkdidtheteacherdo?Explain.

11/29/17

15

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.

11/29/17

16

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

11/29/17

17

5.4WorkandMachines

• MachinesDoWork• Amachineisadevicethatchangesaforce.• Machinesmakeworkeasiertodo.Theychangethesizeofaforceneeded,thedirectionofaforce,orthedistanceoverwhichaforceacts.•  IncreasingForce• Whenusingamachine,asmallforceexertedoveralargerdistancebecomesalargerforceexertedoverasmallerdistance.• Ex:Turningasteeringwheelwithasmallerforceappliesalargerforcetothesmallersteeringcolumn.

5.4WorkandMachines

•  IncreasingDistance• Amachinethatdecreasesthedistancethroughwhichyouexertaforceincreasestheamountofforcerequired.• Ex:Whenyouswingabaseballbat,yourhandsdonottravelasfarastheotherendofthebat.Youapplyalargerforcetothebatoverasmallerdistancewhilethebatappliesasmallerforcetotheballoveralargerdistance.

11/29/17

18

5.4WorkandMachines

• ChangingDirection• Changingthedirectionofaforcecanmakeworkeasierwithoutchangingdistanceormagnitudeoftheforce.• Ex:Hoistingasail,youpulldownonaropetopullthesailup.

5.4WorkandMachines

•  InputandOutputWork• Becauseoffriction,theworkdonebyamachineisalwayslessthantheworkdoneonthemachine.

• WorkInputtoaMachine • Theforceyouexertonamachineiscalledtheinputforce.• Thedistancetheinputforceactsthroughisknownastheinputdistance.• Theworkdonebytheinputforceactingthroughtheinputdistanceiscalledtheworkinput.• workinput=Finput*dinput

11/29/17

19

5.4WorkandMachines

• WorkOutputofaMachine• Theforcethatisexertedbyamachineiscalledtheoutputforce.• Thedistancetheoutputforceisexertedthroughistheoutputdistance.• Theoutputworkofamachineistheoutputforcemultipliedbytheoutputdistance.• workoutput=Foutput*doutput

• Withoutachangetotheinputwork,theoutputworkwillremainthesame.

5.4WorkandMachines

• MechanicalAdvantage• Themechanicaladvantageofamachineisthenumberoftimesthanthemachineincreasesaninputforce.

• Forexample,ifanutcrackerexertsaforceseventimesgreaterthantheinput,thenitsmechanicaladvantageis7.

• Mechanicaladvantagedoesnothaveaunit.• ActualMechanicalAdvantage (AMA)• AMAequalstheratiooftheoutputforcetotheinputforce.• Equation:

11/29/17

20

5.4WorkandMachines

•  IdealMechanicalAdvantage(IMA)•  IMAisthemaximummechanicaladvantagepossibleifthemachinewerefrictionless.• Becausefrictionisalwayspresent,theactualmechanicaladvantageofamachineisalwayslessthantheideamechanicaladvantage.• Equation:

5.4WorkandMachines

• Practice• Astudentworkinginagrocerystoreafterschoolpushesseveralgrocerycartstogetheralongaramp.Therampis3meterslongandrises0.5meters.Whatistheidealmechanicaladvantageoftheramp?• Aconstructionworkermovesacrowbarthroughadistanceof0.50mtoliftaload0.05moffoftheground.WhatistheIMAofthecrowbar?• TheIMAofasimplemachineis2.5.Iftheoutputdistanceofthemachineis1.0m,whatistheinputdistance?

11/29/17

21

5.4WorkandMachines

• Efficiency• Thepercentageoftheworkinputthatbecomesworkoutputistheefficiencyofamachine.

• Becausethereisalwayssomefriction,theefficiencyofanymachineisalwayslessthan100%.

• Equation:

5.4WorkandMachines

• Practice• Youhavejustdesignedamachinethatuses1000Jofworkfromamotorforevery800Jofusefulworkthemachinesupplies.Whatistheefficiencyofyourmachine?

•  Ifamachinehasanefficiencyof40%,andyoudo1000Jofworkonthemachine,whatwillbetheworkoutputofthemachine?

11/29/17

22

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:

11/29/17

23

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

11/29/17

24

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:

11/29/17

25

5.5SimpleMachines

•  InclinedPlanes• Aninclinedplaneisaslantedsurfacealongwhichaforcemovesanobjecttoadifferentelevation.• Examples:Wheelchairramp,boardingrampontoaship• Equation:

5.5SimpleMachines

• Wedge• AwedgeisaV-shapedobjectwhosesidesaretwoinclinedplanesslopedtowardeachother.•  IMA>1• Athinwedgeofagivenlengthhasagreateridealmechanicaladvantagethanathickwedgeofthesamelength.• Examples:zipperteeth,knife,axehead

11/29/17

26

5.5SimpleMachines

• Screw• Ascrewisaninclinedplanewrappedaroundacylinder.• Screwswiththreadsthatareclosertogetherhaveagreateridealmechanicaladvantage.• Thethreadonascrewisusuallymeasuredinthreadsperinchorthreadspercentimeter.• Examples:woodscrews,jarlids,nuts

5.5SimpleMachines

• Pulleys• Apulleyisasimplemachinethatconsistsofaropethatfitsintoagrooveinawheel.• Canchangemagnitude,distance,ordirectionofinputforce.• ThreeTypes

11/29/17

27

5.5SimpleMachines

• FixedPulley• Awheelattachedinafixlocation.• Oftenabletorotateinplace.• Changesthedirectionoftheappliedforce,butnotthemagnitudeordistance.• IMA=1• Examples:flagpole,pulleyusedtopullupblinds

5.5SimpleMachines

• MovablePulley• Awheelattachedtotheobjectbeingmoved(theropeisattachedtoafixlocation).• Ifyouarepullingup,IMA=2• Examples:pulleysusedtohoistsails,skyscraperwindowwashersstandonplatformssuspendedbymovablepulleys.

11/29/17

28

5.5SimpleMachines

• PulleySystem• Combinationsoffixedandmovablepulleys• CanachievehighIMA

• Equation:IMA=#ropesectionssupportingtheloadbeinglifted

5.5SimpleMachines

• CompoundMachines• Combinationoftwoormoresimplemachinesthatoperatetogether.

• Examples:systemofgears,acar,washingmachine