Chapters5&6Combined

5Sec5onsTotal

Energy&EnergyResources

WhatisEnergy

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•  Energy‐istheabilitytocausechange.– Kine5c– Poten5al

•  Kine)cenergy‐energyofmo5on–  Increasesasanobjectmovesfaster

–  Increasesasthemassofanobjectincreases.• Whereelsehaveyouheardthis?

•  Poten5alenergy‐energystoredinanobjectduetoitsposi5on.

Energycomesindifferentforms:

•  Thermalenergy‐increasesastemperatureincreases.

•  Chemicalenergy‐energystoredinchemicalbonds.

•  Radiantenergy‐lightenergy•  Electricalenergy‐fromelectricity•  Nuclearenergy‐comesfromthenucleusofanatom.

Poten5alenergyVS.Kine5cenergy•  MeasuredinJoules.•  Lawofconserva)onofenergy‐energycannotbe

createdordestroyed.

Poten5alenergy=50JKine5cenergy=0J

1.

2. Poten5alenergy=25JKine5cenergy=25J

Poten5alenergy=0JKine5cenergy=50J

3.

ThermalEnergy

•  Manydifferentformsofenergycanbeconvertedintothermalenergy:–  Diges5ngfood(chemicalenergy)‐‐>youstarttogethot&sweat(thermalenergy)

–  Electricityflowingthroughawire(electrical)getshot(thermal).

–  EVERYTHINGHASTHERMALENERGY!–  Actsasamediumforotherenergytransfers

•  Heatiron(thermal)getsredhot&glows(radiant)

Chemicalenergyexamples:

•  Eatfood(bodyconvertsenergyfromfoodintoenergysoyoucanfunc5on)

•  Putgasintoacar(convertsitintokine5cenergysoitcanrun)

Electricalenergy

•  Causebyfastmovingpar5cles.•  Thesepar5cleshavechargesthata`ractandrepeleachother.

•  Thereinterac5oncauseswhatwecallelectricity.

•  Mostmodernhomesrelyonelectricitytofunc5on.

•  Teslavs.Edison

Lightorradiantenergy

•  Lightenergy‐anythingthatproduceslight.•  Fastmoving(186,000m/s)that’s416,082milesperhour.

•  Ourmainsourceofradiantenergyis~93millionmilesaway…ittakes8min20sectoreachus.

Nuclearenergy

•  Radioac5vedecay‐causesbyunstableelectrons&protonssplikngfromatoms

•  Fusion‐2nucleifusetogethertoformaheavieratom

•  Fission‐breaking2nucleiintolighternuclei•  Starsarefueledbyfusion,powerplantsarefueledbyradioac5vedecay,nuclearweaponsusefission.

•  Lead???

EnergyTransforma5ons

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Energyconstantly:

•  Changesfromoneformtoanother•  Ormovesfromplacetoplace

•  Remember:energycannotbecreatedordestroyed‐thatisthelawofconserva5onofenergy

•  Energycanbetransformedfromkine5ctopoten5alenergyandbacktokine5c.

P=0JK=10J

P=10JK=0J

P=5JK=5J

P=5JK=5J

P=0JK=10J

Machines

•  Transformenergyfromoneformtoanother:– Chemicalenergycanbetransferredtokine5c,radiant,thermal,orelectrical

– Electricalenergycanbetransformedtokine5cchemicalelectricalorthermal

– Unlikeotherformsofenergy,THERMALenergyisnoteasytostore.

•  Duringallenergytransforma5onssomeenergyislostduetoTHERMALENERGY.

•  Ifyouareonamovingswingyouwilleventuallystopbecauseofairresistance,whichisfric5on,andyourkine5cenergyistransformedintothermalenergy.

ElectricityProduc5on:

•  Inmostformsofelectricalenergygenera5oninpowerplantsthelast2stepsarethesame:– TheKine5cenergyofsteamturnsaTURBINE.– Thekine5cenergyoftheturbinepowerstheGENERATOR.

Ifyoudidn’tknowalready?

•  Turbine‐setofsteam‐poweredfanbladesthatspinsageneratoratapowerplant.

•  Generator‐devicethattransformskine5cenergyintoelectricalenergy.

PowerPlants

Sourcesofenergy

Sec5on3

•  EnergycomesfromeithertheSUNorfromRADIOACTIVEATOMSwithintheEarth.

FOSSILFUELS

•  Includeoil,naturalgas,&coal– FossilfuelscontainchemicalenergyfromtheSun’sradianenergyviaphotosynthesis.

– Nonrenewableresourcessuchasfossilfuelsareusedupfasterthancanbereplaced.•  ourcoaltodaystartedoffasaplant(~300millionyearsago)

NuclearEnergy

•  ComesfromthenucleiofURANIUMATOMS

h`p://www.pplweb.com/NR/rdonlyres/7C32A442‐3C42‐4978‐9BE4‐7128585258E0/0/nuclear.swf

Hydroelectricity•  Comesfromthepoten5alenergyofwater.•  Isarenewableresource– Meaningitisreplenishedcon5nuously

Alterna5veResources

•  Maybesaferforpeople&theenvironment.•  Willhelpconservefossilfuels

•  Conservingenergywillhelppreventenergyshortages&allowfossilfuelstolastlonger.

SomeAlterna5veResources

•  SolarenergycanbecapturedinthermalcollectorsorPHOTOVOLTAICcollectors.

•  Geothermalenergy‐thermalenergycontainedinhotmagma.

•  Windmillscangenerateelectricitywithoutpollu5ngtheenvironment

Chapter6

ThermalEnergy

Sec5on1

Temperature&ThermalEnergy

Temperature

•  A.Temperatureisthemeasureoftheaveragevalueofthekine5cenergyofthemoleculesinasubstance

•  Thehigherthetemperature,thefasterthemoleculesaremoving.

•  1.Objectstendtoexpandwithincreasedtemperaturebecausetheirmoleculesspeedupandmovefartherapart

•  Objectscontractwhentheyarecooled.–  a.theamountofexpansionorcontrac5ondependsonthematerialandtheamountofchangeintemperature

–  b.Liquidsusuallyexpandmorethansolids.

examples

•  Solids:–  Inthesummer5mepowerlineswillsag,whereasinthewintertheywillbepulledmore5ghtly.

•  Liquids:–  Youprobablybeentoldnevertoputaglassbo`leofsodainthefreezer.Why?Itcanexplodeandyouwillhaveglassalloveryoufreezer.

•  Gases:–  Placeaballooninaverywarmroomanditwillexpand,thenplaceitinaverycoldroomanditwillshrink.

•  2.TemperatureiscommonlymeasuredusingaThermometer.

Thermometer

•  A thermometer is a device that measures the temperature of things.

•  The name is made up of two smaller words: –  "Thermo" means heat –  "meter" means to measure.

•  One of the earliest inventors of a thermometer was probably Galileo.

•  Galileo is said to have used a device called a "thermoscope" around 1600 - that's about 400 years ago!!

Howdoesathermometerwork?•  When you look at a regular outside bulb thermometer,

you'll see a thin red or silver line that grows longer when it is hotter. The line goes down in cold weather.

•  This liquid is sometimes colored alcohol but can also be a metallic liquid called mercury. Both mercury and alcohol grow bigger when heated and smaller when cooled.

•  Inside the glass tube of a thermometer, the liquid has no place to go but up when the temperature is hot and down when the temperature is cold.

•  Numbers are placed alongside the glass tube that mark the temperature when the line is at that point.

Anothertypeofthermometer

•  "spring" thermometer. •  A coiled piece of metal that is sensitive

to heat is used. •  One end of the spring is attached to

the pointer. •  As the air heats, the metal expands

and the pointer moves higher. •  As the air cools, the metal contracts

and the pointer moves lower. •  Typically, these type of thermometers

are less accurate than bulb or digital thermometers.

•  3.Thermometersneednumbersonascaletogiveitatemperaturereading.– a.Fahrenheitscale:• Waterfreezesat32°F

• Waterboilsat212°F

– b.Celsiusscale:• Waterfreezesat0°C• Waterboilsat100°C

– c.Theformulatoconverttemperaturefrom°Fto°Cis:

°C=(5/9)(°F‐32)

Ifitis78°Fintheclassroomhowmany°Cisit?°C=(5/9)(°F‐32)°C=(5/9)(78°‐32)°C=(.55555556)(46)°C=25.6°C

– d.Theformulatoconverttemperaturefrom°Cto°Fis:

°F=(9/5)(°C)+32Iftheclassroomwas21°Cwhatwoulditbein°F?

°F=(9/5)(°C)+32°F=(9/5)(21°)+32°F=(1.8)(21°)+32°F=(37.8°)+32°F=69.8°F°F=70°F

– e.TheKelvinscalegivesthetemperatureof0Ktothelowesttemperatureanobjectcanhave

– knownasABSOLUTEZERO

–  f.FormulafortheKelvinscale

KelvintoCelsius

°C=K‐273_____________________________ CelsiustoKelvin

K=°C+273

•  B.Anobject’sThermalenergyisthesumofthekine5c&poten5alenergyofallthemoleculesintheobject.– 1.Poten5alenergyisenergythatcanbeconvertedintokine5cenergy.•  Poten5alenergychangesasmoleculesmoveclosertogetherorfartherapart.

– 2.Temperatureandthermalenergyaredifferentconcepts•  Thermalenergyisrelatedtothequan5tyofmolecules.

Whyistemperatureandthermalenergydifferent?

•  Letssayyouhad2glassesofwateratexactlythesametemperature.

•  Youpouredthemintoapot.•  Willthetemperatureofthewaterchange?NO•  Willthethermalenergychange?YESwhy?BECAUSETHEREAREMOREMOLECULES.

•  Howcanweknowthisforsure?–  ITTAKESLONGERFORMOLECULESTOHEATUPORCOOLDOWNWHENTHEREAREMOREOFTHEMASOPPOSEDTOLESS.

–  ITTAKESLONGERFORASWIMMINGPOOLOFWATERTOWARMUPINTHEHOTSUNCOMPAREDTOJUSTAGLASSOFWATER.

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Heat

Heat•  A.Heatisthethermalenergythatistransferredfromoneobjecttoanotherwhentheobjectsareatdifferenttemperatures.–  1.Thermalenergyalwaysmovesfromwarmertocoolerobjects.

Howdoweknowthis?Easyexperiment:takesomethingwarmlikehotsoupandputanicecubeinit.Whathappenstotheicecube?

Kitchen5p:Youwanttodefrostafrozensteakwithoutitamicrowavecookingtheedgesevenwhenyouhaveitondefrost:placethefrozenmeatonacastironpan.Castironisheavy,thereforeithaslotsofmolecules.Theheatfromthemoleculeswilltransferintothemeatanddefrostyousteakinaboutanhours5meorless.

•  2.Thetransferofheatbydirectcontactbetweenthepar5clesofasubstanceiscalledCONDUCTION.

•  Conduc5onoccursmosteasilyinsolids,wheremoleculesareclosetogether.

Ifyouplacedapotofwaterandametalspoononahotburner.Thespoonwillgetho`ermuchquicker.Commonsensesaysdon’tpickupthespoonunlessyouareusingahotpad.Sodon’ttrythisathome…ifyouhavenocommonsense!

•  3.HeattransferbyRADIATIONoccurswhenelectromagne5cwavescarryenergythroughspaceorma`er.

Whydoestheroadgethotinthesummer?BECAUSETHESUN’SRAYSTRAVELABOUT92MILLIONMILESTHROUGHSPACEDOSO.

Peoplegototanningbedsandbecometan.Why?BECAUSETHERADIATIONCOOKSTHEIRSKIN.

•  4.CONVECTIONdescribesthetransferofthermalenergybythemovementofmoleculesfromonepart(warmer)ofthematerialtoanother(cooler)part.

– a.Convec5onoccursnaturallyashotgasorliquidmovesfromoneplacetoanother

– Windiscausedbyconvec5onintheair

– Risingwarmerairformsaconvec5oncyclewithfallingcoolingair.

•  WherewecanseeConvec5ontakingplace.•  Wind:airheatsuplandinoneareamorethananother.Likeyousawontheotherpage.

•  Inthemantle,IntheSun,EveninaBowlofsoup.

•  B.CONDUCTORSarematerialsthattransferheatreadily.– Metalssuchascopperandgoldarethebestheatconductors

•  C.INSULATORSarematerialsthatdoesnottransferheatreadily.– Liquidsandgasesareusuallybe`erinsulatorsthansolids.

•  D.Objectsabsorbheatatdifferentratesdependingonwhatmaterialstheyaremadeof.–  1.SPECIFICHEAT‐amountofheatneededtoraisethetemperatureof1kgofasubstanceby1°C

– 2.Moreheatisneededtochangethetemperatureofamaterialwithahighspecificheat(suchaswater)thanonewithalowspecificheatsuchassand.

Land&SeabreezesDay5mewhenthesunisshiningthegroundheatupmuchfasterthanthewaterdoes.

80°F70°F

60°F70°F

Night5methelandcoolsmuchquickerthanthewaterdoes

•  E.ThermalPollu)oncausedbyaddingwarmerwatertoabodyofwater.– 1.Thermalpollu5oncankillfishandotheraqua5corganismsduetoareduc5oninoxygeninwarmerwater.

– 2.Thermalpollu5oncanbereducedbycoolingwaterfromfactories,powerplants,andrunoffbeforeitisreleasedintoabodyofwater.