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作者： (美)坦南鲍姆(Tanenbaum,Andrew S.)著;于志强,冯化中译
出版社：晓园出版社(北京:世界图书出版公司,1993.6重印)
简介：
片断：
PROLOGUE
AUnifiedViewof
PhysicalProcesses
Heraclides(550-480)
Everythingflows.WaterandairflowonthesurfaceoftheEarth,wheretheycre-
atethemultitudeofphenomenaweknowfromeverydaylife.Windscanimpart
theirmotiontothewateroftheoceans,andinafar-awayplace,thismotioncan
bepickedupagainthroughtheactionofthewaves.Theseprocessesaremain-
tainedbytheradiationpouringoutfromthesurfaceofthesun;lightflowsfrom
therethroughspace,andsomeofitisinterceptedandabsorbedbyourplanet.
Bothinnatureandinmachines,heatisproducedandtransportedfromplaceto
place.Inelectricalmachines,wemakeelectricityflowinanimitationofitsflow
intheatmosphere,andinreactors,chemicalsubstancesflowwhileatthesame
timeundergoingchange.Today,weevenseelifeasgovemedbyflowprocesses.
Weshalltakethisobservationasthestartingpointofourinvestigationofnatural
andmanmadephenomena.Itleadstooneofthemostgeneraldescriptionofna-
tureweknowtoday.Thereareafewphysicalquantitieswhichcanflowintoand
outofsystems,whichcanbeabsorbedandemitted,andwhichcanbeproduced
anddestroyed.Electricalchargeistransportedinelectricalprocesses,andmass
andsubstancellowingravitationalandchemicalphenomena,respectively.In
continuummechanics,motionisseenastheexchangeoflinearandangularmo-
mentum.Thermalphysicsisthescienceofthetransportandtheproductionof
heat.Oneofthegreatadvantagesofthisdescriptionofnatureisthatitrelatesthe
differentphenomena,whichleadstoaneconomicalandunifiedviewofphysical
processes.Ittumoutthatclassicalcontinuumphysicsisaprecisemethodofex-
pressingthispointofviewformacroscopicsystems(seeSectionP.5).
Inthischapter,weshallpresentsomeexamplesofintroductoryphysics,mostof
whichyoushouldbefamiliarwith.Weshalluseasthemaintooltheimagesand
thelanguagefoundincontinuumphysics.Inthisway,wehopetopreparethe
groundfortheapproachtothennodynamicswhichyouwillfindinthisbook.
Note,however,thatthischapterisacondensedoverview,notatext.Afterread-
ingSectionP.1youmaywanttoventuredirectlyintothemainbodyofthebook,
inwhichcaseyoumightwishtoreturntothischapterlateron.Eitherway,we
believeyouwillfinditadvantageoustodrawcomparisonsbetweendifferent
fieldsofphysicsasoftenaspossibleduringyourjoumeythroughthennodynam-
ics.
Whatisthisunifiedapproachtophysics?Inshort,itisbasedonananalogywith
continuumphysics.First,wehavetoagreeonwhichphysicalquantitiesweare
goingtouseasthefundamentalorprimitiveones;ontheirbasisotherquantities
aredefined,andlawsareexpressedwiththeirhelp.Second,therearethefunda-
mentallawsofbalanceofthequantitieswhichareexchangedinprocesses,such
asmomentum,charge,oramountofsubstance;wecallthesequantitiessubstan-
celike.Third,weneedparticularlawsgovemingthebehaviorof,ordistinguish-
ingbetween,differentbodies;theselawsarecalledconstitutiverelations.Last
butnotleast,weneedameansofrelatingdifferenttypesofphysicalphenomena.
Thetoolwhichpennitsustodothisisenergy.Weusetheenergyprinciple,i.e.,
thelawwhichexpressesourbeliefthatthereisaconservedquantitywhichap-
pearsinallphenomena,andwhichhasaparticularrelationshipwitheachofthe
typesofprocesses.
Tointroducetheelementsoftheoseslistedabove,weshallbeginwithacom-
parisonoftheflowofwaterandAelectricalcharge.
P.lTheFlowofaterandCharge
Weallarefamiliarththeflowofwaterinsimplesettings,suchasthefilling
orthedischargingcontainersthroughpipes(Figure1).Bylookingataspecial
examplewewillbeabletoidentiiytheelementsofaphysicaltheorywhichal-
lowustocalculatesuchthingsasthecnrrentofwaterthroughapipe,thepres-
sureatvariouspointsinthefluid,andthetimerequiredtodischargeacontainer.
Theanalysisalsowilltellusthatthesystemandtheprocessesitmayundergo
areverysimilartowhatweknowfromelectricity.Bycomparinghydraulicand
electricalsystemsweshallleamaboutthepowerofanalogiesbetweendifferent
fieldsofphysics.
P.l.lPhyslcalQuantltles
Ourfirstquestionmustbewhichphysicalquantitieswecanuseasbasisfora
quantitativedescriptionoftheflowofwaterintoandoutofcontainers.Weshall
havetodothesamefortheelectricalsystem.ThechoiceofFundamentalorprim-
itivequantitiesisnotunique.Wesimplyhavetobeginsomewhere,insomeway.
Wecertainlyneedameasureoftheamountofwaterinacontainer.Therearesev-
eralpossiblechoices.Thesimplestoftheseisthevolumeofthewater.Another
thatcomestomindquicklyisthemassofthewater.Finally,chemistsmightbe
inclinedtomeasuretheamountofwateronthebasisofitsamountofsubstance
(SectionP.2.7).
