机械工程导论(双语)课件2讲解学习.pptx

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1、mechanicalengineeringAnintroductionto1Lecturer:LiuJu-rongCHAPTER2Problem-SolvingSkillsOVERVIEW1UNITSYSTEMSANDCONVERSIONS23DIMENSIONALCONSISTENCY2SIGNIFICANTDIGITS4ANERROROFUNITSONTHEWAYTOMAR5APPROXIMATIONINENGINEERING6PROBLEM-SOLVINGMETHODOLOGY71OVERVIEW----theimportantofun

2、it4Howimportantaunitis?Eachquantityinmechanicalengineeringhastwocomponents:anumericalvalueandaunit.Oneissimplymeaninglesswithouttheother,andpracticingengineerspayascloseandcarefulattentiontotheunitsinacalculationastheydotothenumbers.1OVERVIEW---Theabilitytobeavailableinthis

3、chapter5Afterstudy,whatshouldyoubeabletohave?Reportbothanumericalvalueanditsunitineachcalculationthatyouperform.ListthebaseunitsintheUnitedStatesCustomarySystemandtheSystemInternationald‘Units,andstatesomeofthederivedunitsusedinmechanicalengineering.Understandtheneedforprop

4、erbookkeepingofunitswhenmakingengineeringcalculationsandtheimplicationsofnotdoingso.ConvertnumericalquantitiesfromtheUnitedStatesCustomarySystemtotheSystemInternationald‘Units,andviceversa.Checkyourequationsandcalculationstoverifythattheyaredimensionallyconsistent.Understan

5、dhowtoperformorder-of-magnitudeapproximations.2UNITSYSTEMSANDCONVERSIONS-UnitSystemwhatisUSCSandSI?6Engineersspecifyphysicalquantitiesintwodifferent,butconventional,systemsofunits:theUnitedStatesCustomarySystem(USCS)andtheInternationalSystemofUnits.Practicingmechanicalengin

6、eersmustbeconversantwithbothunitsystems.2UNITSYSTEMSANDCONVERSIONS-anexampleKeepingTrackofUnitsonFright1437InJulyof1983,AirCanadaFlight143wasenroutefromMontrealtoEdmonton.TheBoeing767hadthreefueltanks,oneineachwingandoneinthefuselage,whichsuppliedtheplane'stwojetengines.vol

7、ume(L),weight(lb),mass(kg)Totalfuel22,300kilograms(kg)Howmuchfuelshouldbeadded?Fuelintanks7682liters(L)Boeing767pounds(lb);kilograms1.77lb/L1.77kg/L9000liters16,000liters2UNITSYSTEMSANDCONVERSIONS-BaseandDerivedUnitswhatisbaseunits?Whatisderivedunits?8Abaseunitisafundamenta

8、lquantitythatcannotbefurtherbrokendownorexpressedintermsofanysimplerelements.Baseu