1.physical-quantities-and-unit

PhysicalQuantities&UnitsSubjects1.Theexpressionofphysicalquantities2.7basephysicalquantitiesandtheirSIunit3.Prefixesandunitconversion4.Derivedquantities5.SignificantdigitsWhatarePhysicalQuantities?Howbigisit?Howheavyisit?Wheredoesitgrow?Whatistheaveragemassofanapple?(150g)Magnitude(numericalvalue)UnitProductofanumberandaunit×7basephysicalquantitiesMassLengthTimeElectriccurrentTemperatureAmountofsubstanceLuminousintensityStandardInternational(SI)Unitof7BaseQuantitiesWhyweneedtheSIunits?Thestorygoes…KingQueenWhyweneedtheSIunits?carpenterBureauInternationaldesPoidsetMesures(TheInternationalBureauofWeightsandMeasures)国际计量局LocatedinParisFranceThetaskoftheBIPMistoensureworld-wideuniformityofmeasurementsandtheirtraceabilitytotheInternationalSystemofUnits(SI).standardinternationalunit!Forexample:Diameterofgalaxy100,000,000,000,000,000,000mScientificNotation：1020m•Tentothepoweroftwenty•Tentothetwentiethpower•Thetwentiethpoweroften•10tothe20Diameterofatom：0.0000000001mScientificNotation10-10m•Tentothepowerofminus/negativeten•Tentotheminus/negativetenthpower•theminus/negativetenthpoweroften•Tentotheminus/negativeten(10tothe-10)Aprefixaddedtoaunitmeansthattheunitismultipliedbyanumericalvaluerepresentedbytheprefix.PrefixesWeuseprefixestochangethesizeofaunitPrefixesandTheirSymbolsValueNameSymbol103Kilok106MegaM109GigaG1012TeraTValueNameSymbol10-1Decid10-2Centic10-3Millim10-6Microμ10-9Nanon10-12picop10-15femtofBiggerSmallerUnitConversion1.Howmanygramsaretherein1kilogram?1kg=1000g=103g2.Howmanymicrosecondsaretherein1second?1s=106μs3.Writedownthefollowinginkm:2000m=200m=2×104m=2km0.2km20kmDiameterofatom：0.1nmRadiofrequency：107.9MHzHarddrivecapacity：640GB(Gigabyte)1TB=1024GB1GB=1024MB1MB=1024kB1kB=1024B1GB=1048576000B≈109BThemassofoneelephantis5ton1t=1000kg=106g=1Mg1h=60min1min=60s1s=1000ms1ms=1000μsUnitsofTimethedistancethatlighttravelsinavacuumin1yearThesecondisnowdefinedintermsofsomethingthatneverchanges:thefrequencyofanoscillationwhichcanoccurinthenucleusofacaesium(铯)atom.PhysicalQuantitiesBaseorfundamentalquantitiesDerivedquantities7basequantities：MassLengthTemperatureTimeElectriccurrentAmountofsubstance(物质的量)Luminousintensity（发光强度）Allotherquantitiescanbeobtainedfromthemultiplicationordivisionofbasequantities.MassandAmountofsubstanceMass:ameasureoftheamountofsubstanceinanobject.(physical)(it’shardtodefinedirectly)Twoeffect:gravity.Thegreaterthemassthebiggerthegravity.thegreaterthemass,hardertochangeit’smotionconditionAmountofsubstance:measuresthesizeofanensembleofelementaryentities.chemicalamount.DerivedQuantitiesv=takentimentdisplacemeUnit：m/s(ms-1)orkm/h(kmh-1)CombiningUnitVelocityUnits：m3(cubicmeter)cm3(cubiccentimeter)VolumeV=hightarea3lengthOtherunits：Lorl(liter)mLorml(milliliter)1L=1000mL=1000cm3Unit：g/cm3orkg/m3ρ=volumemass3lengthmassDensityg/cm3=1000kg/m3kgm/s2newton,Nkg/(ms2)pascal,Pakgm2/s2joule,JJupiteristhefifthplanetfromtheSunandthelargestplanetintheSolarSystem.It’smeanradiusisabout69900km.Itisagasgiant,It’saveragedensityis1.326g/cm3.Selfrotationperiodis9h55m30s.What‘sthevolume,mass,rotationperiodofJupiter?(SIunit)V=4/3*Pi*r3=1.4306×1024m3M=V=1.8970×1027kgT=35730s=3.573×104sWhataboutEarth？Radiusabout6371km，averagedensity5.514g/cm³，rotationperiod23h56m4s.EarthandJupiterinTheSolarSystem•Wecancheckwhetheronephysicsformulaiscorrectornotbycheckitsdimensions.example：•Wecanalsoguesstheunitofanewquantitybycheckingthedimensionsonbothsideoftheformula.•Exercise:theresistiveforceFactingonasphereofradiusrmovingatspeedvthroughaliquidisgivenbyF=cvr,wherecisaconstant,what’stheunitofc?2LTgApplicationsofUnitsg2LTghasaunitofm/s2Answer5.6.Unitsfromlargest9.a)1.564mb)1.75kgc)d)e)f)关于作业1.Prefix部分，要熟悉每个prefix代表的tentopoweroftheX，而且要能迅速判断它的大小2.大家要会用unit来判断一个公式是否错误并能求解处未知物理量的单位3.学会进行单位换算4.Scientificnotation部分，要能把给的物理量用scientificnotation/standardform的形式表示。Whenmeasuring,onedigitisalwaysestimateddependingoncalibration.Example14.3cmNon-zerodigitsarealwayssignificant.22cm(2s.d.)and22.3cm(3s.d.)Withzeroes,1.Zeroesplacedbeforeotherdigitsarenotsignificant(0.0462s.d.)2.Zeroesplacedbetweenotherdigitsarealwayssignificant(4009m4s.d.)3.Zeroesplacedafterotherdigitsbutbehindadecimalpointaresignificant(7.90s3s.d.)4.Zeroesattheendofanumberaresignificantonlyiftheyarebehindadecimalpointasin(3).Otherwise,itisimpossibletotelliftheyaresignificant.8200matleast2s.d.butnotsure，soweusescientificnotationtoplacesignificantzeroesbehindadecimalpoint:8.200×1034s.d.8.20×1033s.d.有效数字：从第一个非0的数字开始数，数到最后一位!SignificantDigits•Youcanonlyaddorsubtracttotheleastprecisemeasurement.34.89m+6.2m41.09m41.1misthefinalanswer.Wegetridofthe9becauseitisaddedtoanunknown.Exercise:1.6km+1.62m+1200cm10.8g-8.264gAdding