Energy-transfers

Name:Think1-21.Rubyourhandsfast2.TurnonthelightWhyyourhandsbecomewarm?Whathappened?Think3Whytheballjumpslowerandloweruntilitstops?EnergytransfersandtransformationsEnergytransfer能量转移Energytransformation能量转换ChemicalEnergy化学能Kinetic(movement)energy动能Heatenergy热能①Heatenergyistransferredfromhotwaterintoair.②somechemicalenergystoredinfoodistransformedtokineticenergy;someistransformedintoheattokeepthebodywarm.Think1-2Kineticenergy动能Heatenergy热能Heatenergy热能Kineticenergy动能Electricalenergy电能Energyistheabilityofaphysicalsystemtodowork.Theunittomeasureenergyandworkisjoule(J),namedafterJamesPrescottJoule,anEnglishphysicist.1kJ=1000JWhatisenergy?Howenergyusehasincreased?WaterPotentialEnergySunlightSolarEngergyWindmillWindEnergyCoalChemicalEnergyTherearedifferentformsofenergyinthenature.Peoplecanmakefulluseofenergytomakelifeeasier.Pleaseturntopage225,chapter16.Buildingslitbycandles,oillamps&gaslightsCoal&woodusedasfuelforfiresPeopleandgoodstransportedbycarriagesandcartspulledbyhorsesTrainspulledbysteamlocomotivesSomepeoplewalkedAsquareinManchester,England,120yearsago(Figure16.1)TimesSquareinNewYorktoday(Figure16.2)BuildingslitbyelectricityA/Cpoweredbyelectricitytocoolinsummer;heaterstowarminwinterPeopleandgoodstransportedbycars,vans,trucks&busespoweredbypetrolordieselenginesTrainspulledbyalocomotivewithanelectricmotorSomepeopletakeaircraftusingkeroseneHowtoshowenergytransformations1.Energytransferdiagrams能量转移图EnergyconverterortransducerEnergyinputandoutputstrainenergy应变能catapult弹弓kineticenergy动能Example:ReleasingacatapultHowtoshowenergytransformations2.Sankeydiagrams桑基图Thewidthofarrowindicatestheamountofenergyitrepresents.Example:Energyinacarenginekineticenergy80kJChemicalenergyinpetrol200kJwasteenergy120kJWaterPlantsandenergy1桑基图Figure16.6Photosynthesis光合作用Energystoredinseedsisusedastherootgrowsandseeksoutwater;thentheshootusesthestoredenergytogrowupthroughthesoil,reachesthesurfaceandsendsoutleaves.Plantsandenergy2Plantsandenergy3Photosynthesis(光合作用）:theprocessofmakingfoodusinglightenergyPlantsandenergy4PlantherbivorousanimalcarnivorousanimalsChemicalenergytransfersEnergyandourselves1Allfoodscontainenergy.Unit:joule(J)1kJ=1000JEnergyandourselves2Respiration(呼吸作用）:theprocessofchemicalenergyinfoodreleased•Chemicalenergyoxygenwatercarbondioxidesweaturine•Movementenergy•HeatenergyGeneratingenergyMichaelFaraday(1971-1867)EnglishphysicistHediscoveredthatanelectriccurrentcouldbemadetoflowinawireifthewirewasmadetomovethroughamagneticfield（磁场）.Howisthediscoveryusedinourlife?1.Thebicycledynamo自行车发电机Bicycledynamo2.Thepowerstationgenerator电站发电机Pleaseturntopage230(Figure16.10)Think3Whytheballjumpslowerandloweruntilitstops?Energyisnotdestroyed,itjustchangesform.LawofConservationofEnergy能量守恒定律Energycannotbemadeordestroyed,itcanonlybechangedfromoneformtoanother.but…?ButsomeinventorshavetriedtodefytheLawofConservationofEnergy!Perpetualmotionmachine(overbalancedwheel)永动机（失衡的轮子）Canitrunlikethisperpetually?Ofcoursenot!Why?SummaryWhenanenergytransformationtakesplace,someenergyisalwayslostasheat(thermal)energy.EnergytransferscanbeshownbyenergytransferdiagramsandSankeydiagrams.Energyandworkaremeasuredintheunitcalledjoule(J)Photosynthesisandrespiration.Electricitygeneration:bicycledynamoandpowerstationgenerator.TheLawofConversationEnergy