Engineering Basic Mechanics I Statics 工程基础力学Ⅰ 静力学 课件 Chapter 1 Fundamentals of Statics and Force Analysis of Objects

StaticsStaticsofrigidChapter1FundamentalsofStaticsandForceAnalysisofObjectsHowdoforceanalysisinabody1.PrinciplesofStatics:

●Theparallelogramlawofforce.

●Sufficientconditionfortwoforcesequilibriumonarigidbody.●PrincipleofPlusorMinusanEquilibriumForceSystem.

ForcetransmissibilitytheoremThree-forceequilibriumconfluencetheorem

●PrincipleofActionandReaction

●PrincipleofSolidification2.Somereactiveforces:Somereactiveforces:

(1)Flexiblecable(arope,string,chain,strapordrivingbeltwithconstantlengthandnegligibleweight)

Onlytensioncanbeappliedonaflexiblecable,sothereactiveforcesactalongtheflexiblecable

atthe

contactpointanddirectingawayfromthebody.

(2)SmoothcontactsurfaceThereactiveforceactsnormaltothesurfaceatthepointofcontactandtowardtothebody.

Arollersupportisequivalenttoafrictionlesssurface.Thereactiveforceisnormaltothesupportingsurface.

(3)Rollersupport(4)Pinsupport

Twoormorebodiesareconstrainedbyinsertingaslightlysmallerpinintotheholes.

Commonlytwoperpendicularcomponentsareusedtorepresentthereactiveforces.

(5)FixedhingesupportFixedhingesupportissimilartopinsupport.

(6)Fixed-endsupportAfixed-endsupportpreventsallmotionsofthebody,soitintroducestwocomponentsofaforceandamoment.

(7)Two-forcemembers

Whenabody(oramember)inequilibriumissubjectedtonocouplemomentsandforcesareappliedatonlytwo

points

onthebody(ormember),thebody(ormember)iscalledatwo-forcebody(ortwo-forcemember).Theproceduretodoforceanalysesinbody:(1)Freethebodyfromitssurroundingsanddrawasketchofit;(2)Drawandlabelallappliedforcesonthesketch;(3)Drawandlabelthereactionsduetoeachsupport.Ifthesenseofareactionisunknown,itshouldbeassumed.

TheweightsofbarsABandACarenegligible.ForceFisappliedatthebarAB.RopeDEisweightless.DrawtheforcesforAB,BCandentiresystem.FABCDEHExample1(1)DrawthefrocesforAB

Solution:FABCDEHABHDFAyFFAxFBACEFCFABCDEH(2)DrawtheforcesforACABCDEHFFBFCFABCDEH(3)DrawtheforcesfortheentiresystemSelectthepartofstudy(oralltherigidbodysystem).StepsofdrawingforcesinabodySeparatethepart(all)fromthebodysystem.D