物理学专业英语.ppt

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1、BasicConceptofPhysicsUnitsanddimensionsPhysicalquantitySayaplankis2meterslong.Thismeasurementiscalledaphysicalquantity.Inthiscase,itisalength.Itismadeupoftwoparts:2mMagnitude(number)unitNote:‘2m’reallymeans‘2×meter’,jusas,inalgebra,2ymeans‘2×y’SIbaseunitsScientificmeasurementsaremadeusingSIunits(sta

2、ndingforSystèmeInternationald'unités).Thesystemstartswithaseriesofbaseunits,themainonesbeingshowninthetablebelow.Otherunitsarederivedfromthese.PhysicalQuantityUnitNameSymbollengthMetermmasskilogramkgtimesecondscurrentampereAtemperaturekelvinKamount*molemol*:Inscience,‘amount’isameasurementbasedonthe

3、numberofparticles(atoms,ionsormolecules)present.Onemoleis6.02×1023particles,anumberwhichgivesasimplelinkwiththetotalmass.Forexample,1mole(6.02×1023)ofcarbon-12hasamassof12grams.6.02×1023iscalledtheAvogadroconstant.SIderivedunitsThereisnoSIbaseunitfrospeed.However,speedisdefinedbyanequation.Ifanobjec

4、ttravels12min3s:Theunitsmandshavebeenincludedintheworkingaboveandtreatedlikeanyothernumbersoralgebraicquantities.Theunitms-1isanexampleofderivedSIunit.Itcomesfromadefiningequation.Thereareotherexamplesbelow.Somederivedunitsarebasedonotherderivedunits.Andsomederivedunitshavespecialnames.Forexample,1j

5、oulepersecond(Js-1)iscalled1watt(W).PhysicalquantityDefiningequation(simplified)derivedunitSpecialsymbol(andname)speeddistance/timems-1-accelerationspeed/timems-2-forcemass×accelerationkgms-2N(newton)workforce×distanceNmJ(joule)powerwork/timeJs-1W(watt)pressureforce/areaNm-2Pa(pascal)densitymass/vol

6、umekgm-3-chargecurrent×timeAsC(coulomb)voltageenergy/chargeJC-1V(volt)resistancevoltage/currentVA-1Ω(ohm)Prefixes:PrefixescanbeaddedtoSIbaseandderivedunitstomakelargerorsmallerunits.PrefixSymbolValuePrefixSymbolValuepicop10-12kilok103nanon10-9megaM106microμ10-6gigaG109millim10-3teraT1012Forexample:1

7、mm=10-3m1km=103mNote:1gram(10-3kg)iswritten‘1g’andnot‘1mkg’.Dimensions:Herearethreemeasurement:Length=10marea=6m2volume=4m3Thesethreequantitieshavedimensionsoflength,lengthsquared,andlengthcubed.Using