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1、3Energy:behavior,phenomenaandenvironmentsAlthoughweoftenimaginematerialsasthingsthatcanbeweighed,measuredanddescribed,andthusastangibleartifacts,ourprimaryinterestasdesignersisinhowmaterialsbehave.Asteelcolumnbecomesusefulwhenitsupportsaload.Apaneofglassismeaningfulwhenittransmitslight.Whenwechoo
2、seamaterial,weinherentlychooseitforitsinteractionwithsometypeofenergystimulus,andthisistrueevenforthosematerialsthatwesimplywishtoview,suchasthoseinasculpture.Asaresult,nodiscussionofmaterialscanbecompletewithoutanunderstandingofenergy.3.1FundamentalsofenergyWhatisenergy?Thisisadifficultquestion,
3、asenergyisnotamaterialthingatall,eventhoughitisthefundamentaldeterminantofallprocessesthattakeplaceamongandbetweenallentities.Wheneveranentity–fromanatomtoanecosystem–undergoesanykindofchange,energymusttransferfromoneplacetoanotherand/orchangeform.Forexample,heatmustbetransferred–addedorremoved–f
4、orthetemperatureofanobjecttochange,andtheformofenergymustchangefromkinetictoelectricalwhenaturbinerotatesashaftinagenerator.Conceptually,allformsofenergycanbedividedintotwogenericclasses:*Potentialenergy:storedenergythatcanflow.Theenergythatisstoredbyvirtueofposition,bending,stretching,compressio
5、n,chemicalcombination.Examplesincludewaterbehindadam,boulderontopofahill,acoiledspring,gasoline.*Kineticenergy:energythatisflowing.Theenergyofmotionthatmovesfromhighpotentialentitiestolowpotentialentities.Examplesincludewaterfallingoveradam,aboulderrollingdownahill,thecombustionofgasolineinanengi
6、ne.Withinthesetwoclasses,energytakesmanydifferentforms,andeachformischaracterizedbyafundamentalvariablethatbecomesusefulasenergyonlywhendifferencecomesintoplay.Withoutadifferencebetweenonestateandanother,energycannotflow.Asaresult,energycanonlybequantifiedandmeasuredasitmovesorbyitspotentialtomov
7、e.46Energy:behavior,phenomenaandenvironmentsSmartMaterialsandNewTechnologiesHEATdrivenbytemperaturedifferenceWORKdrivenbypressuredifferencePOTENTIAL:drivenbyheightdifferenceELECTRICAL:drivenbychargedifferenceKINETIC:dr
