机械工程导论(双语)课件 参赛课件.pptx

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1、mechanicalengineeringAnintroductionto1Lecturer:LiuJu-rong参赛选手：****CHAPTER2Problem-SolvingSkillsOVERVIEW1UNITSYSTEMSANDCONVERSIONS23DIMENSIONALCONSISTENCY2SIGNIFICANTDIGITS4ANERROROFUNITSONTHEWAYTOMAR5APPROXIMATIONINENGINEERING6PROBLEM-SOLVINGMETHODOLOGY7Vocabula

2、ry3Torque扭矩thermalconductivity热导率shearstress剪应力fluidviscosity流体的粘度elasticmodulus弹性模量kineticenergy动能Reynoldsnumber雷诺数1OVERVIEW----theimportantofunit4Howimportantaunitis?Eachquantityinmechanicalengineeringhastwocomponents:anumericalvalueandaunit.Oneissimplymeaning

3、lesswithouttheother,andpracticingengineerspayascloseandcarefulattentiontotheunitsinacalculationastheydotothenumbers.1OVERVIEW---Theabilitytobeavailableinthischapter5Afterstudy,whatshouldyoubeabletohave?Reportbothanumericalvalueanditsunitineachcalculationthatyoup

4、erform.ListthebaseunitsintheUnitedStatesCustomarySystemandtheSystemInternationald‘Units,andstatesomeofthederivedunitsusedinmechanicalengineering.Understandtheneedforproperbookkeepingofunitswhenmakingengineeringcalculationsandtheimplicationsofnotdoingso.Convertnu

5、mericalquantitiesfromtheUnitedStatesCustomarySystemtotheSystemInternationald‘Units,andviceversa.Checkyourequationsandcalculationstoverifythattheyaredimensionallyconsistent.Understandhowtoperformorder-of-magnitudeapproximations.2UNITSYSTEMSANDCONVERSIONS-UnitSyst

6、emwhatisUSCSandSI?6Engineersspecifyphysicalquantitiesintwodifferent,butconventional,systemsofunits:theUnitedStatesCustomarySystem(USCS)andtheInternationalSystemofUnits.Practicingmechanicalengineersmustbeconversantwithbothunitsystems.2UNITSYSTEMSANDCONVERSIONS-an

7、exampleKeepingTrackofUnitsonFright1437InJulyof1983,AirCanadaFlight143wasenroutefromMontrealtoEdmonton.TheBoeing767hadthreefueltanks,oneineachwingandoneinthefuselage,whichsuppliedtheplane'stwojetengines.volume(L),weight(lb),mass(kg)Totalfuel22,300kilograms(kg)How

8、muchfuelshouldbeadded?Fuelintanks7682liters(L)Boeing767pounds(lb);kilograms1.77lb/L1.77kg/L9000liters16,000liters2UNITSYSTEMSANDCONVERSIONS-BaseandDerivedUnitswhatisb