理论力学中英文第一章

06.08.202006.08.2020NanchangHangkongUniversity1A静力学引言IntroductiontoStatics06.08.202006.08.2020NanchangHangkongUniversity2A静力学Statics：静力学是研究物体的受力分析、力系的等效替换（或简化）、Staticsisdefinedasasubjectwhichstudytheforceanalysis,reductionofforcesystem建立各种力系的平衡条件的科学．andestablishtheequilibriumequationsofvariousforcesystem.06.08.202006.08.2020NanchangHangkongUniversity3A1、物体的受力分析：ForceAnalysis分析物体（包括物体系）受哪些力，每个力的作用位置和方向，并画出物体的受力图．Analyzetheforcesactingonthebody,andidentifythemagnitude,directionandactivepointoftheforcesdrawaFree-bodydiagram.2、力系的等效替换（或简化）：Reductionofforcesystem用一个简单力系等效代替一个复杂力系。Acomplexforcesystemisreplacedbyasimpleone.06.08.202006.08.2020NanchangHangkongUniversity4A3、建立各种力系的平衡条件：Establishtheequilibriumequationsofvariousforcesystem建立各种力系的平衡条件，并应用这些条件解决静力学实际问题．Practicalproblemsissolvedbyusingtheestablishedequilibriumequations.几个基本概念：FundamentalConcepts刚体：Rigidbody在力的作用下，其内部任意两点间的距离始终保持不变的物体.Arigidbodyisacombinationofalargenumberofparticlesoccupyingfixedpositionswithrespecttoeachother.06.08.202006.08.2020NanchangHangkongUniversity5A力Force物体间相互的机械作用，作用效果使物体的机械运动状态发生改变。Aforcerepresentsthemechanicalactionofonebodyonanother.Themechanicalmotionstateofthebodycanbechangedbyit.力的内效应和力的外效应：Theeffectofactionoftheforceconsistsofinternaleffectandexternaleffect.力的三要素：大小、方向、作用点。力是矢量．Threefactorsofforcesaredefinedasmagnitude,directionandpointofapplication.Forcesarevectors.06.08.202006.08.2020NanchangHangkongUniversity6A力系Forcesystem一群力可分为：平面汇交（共点）力系；平面平行力系；平面力偶系；平面任意力系；空间汇交（共点）力系；空间平行力系；空间力偶系；空间任意力系。Forcesystemisdefinedasagroupofforceswhichactonthesamebody.ClassificationofforcesystemCoplanarforcesystemcanbeclassifiedascoplanarconcurrentforcesystem,coplanarparallelforcesystem,coplanarforce-couplesystemandgeneralcoplanarforcesystem.Forcesinspacecanbeclassifiedasspatialconcurrentforcesystem,spatialparallelforcesystem,spatialforce-couplesystem,generalspatialforcesystem.06.08.202006.08.2020NanchangHangkongUniversity7A平衡Equilibrium物体相对惯性参考系（如地面）静止或作匀速直线运动。Thebodyisinequilibriumifitremainsatrestormoveswithaconstantspeedinastraightlinerelativetotheinertialreferenceframe.06.08.202006.08.2020NanchangHangkongUniversity8A第一章静力学公理和物体的受力分析Chapter1AxiomsofStaticsandFree-bodyDiagram§1-1静力学公理Section1.1AxiomsofStatics06.08.202006.08.2020NanchangHangkongUniversity9A公理1力的平行四边形法则Axiom1Theparallelogramlaw作用在物体上同一点的两个力，可以合成为一个合力Twoforcesactingonthesamepointofabodycanbereplacedbyaresultantforce合力的作用点也在该点，合力的大小和方向，由这两个力为边构成的平行四边形的对角线确定，如图所示。.Theresultantforcecanbeobtainedbyconstructingaparallelogram,usingthetwoforcesastwoadjacentsidesoftheparallelogram.Thediagonalthatpassesthroughthepointofapplicationoftwoforcesrepresentsthemagnitudeanddirectionoftheresultantforce.06.08.202006.08.2020NanchangHangkongUniversity10A合力(合力的大小与方向)(矢量的和)Resultantforce(themagnitudeanddirectionoftheresultantforce)(thevectorsum)21FFFR21FFFR亦可用力三角形求得合力矢Resultantforcealsocanbedeterminedbyforcetrianglerule.06.08.202006.08.2020NanchangHangkongUniversity11A公理2二力平衡条件Axiom2Equilibriumconditionsoftwoforces作用在刚体上的两个力，使刚体保持平衡的必要和充分条件是：这两个力的大小相等，方向相反，且作用在同一直线上。Thesufficientandnecessaryequilibriumconditionsoftwoforcesactingonarigidbodyarethatthetwoforceshavethesamemagnitudeandthesamelineofactionbutoppositesense.21FF06.08.202006.08.2020NanchangHangkongUniversity12A公理3加减平衡力系原理Axiom3Theprincipleofadditionandsubtractionofequilibriumforcesystem在已知力系上加上或减去任意的平衡力系，并不改变原力系对刚体的作用。Therigidbodywillremainunchangedifaequilibriumforcesystemisaddedorsubtractedfromtheoriginalforcesystemactingontherigidbody.06.08.202006.08.2020NanchangHangkongUniversity13A推理1力的可传性Deduction1Theprincipleoftransmissibility作用于刚体上某点的力，可以沿着它的作用线移到刚体内任意一点，并不改变该力对刚体的作用。Theconditionsofequilibriumorofmotionofarigidbodywillremainunchangedifaforceactingatagivenpointoftherigidbodyisreplacedbyaforceofthesamemagnitudeandsamedirection,butactingatadifferentpoint,providedthatthetwoforceshavethesamelineofaction.06.08.202006.08.2020NanchangHangkongUniversity14A作用在刚体上的力是滑动矢量，Theforceisaslidingvectorifitactsonarigidbody.力的三要素为大小、方向和作用线．Thethreefactorsofaforceactingonarigidbodyaremagnitude,directionandthelineofitsaction.推理2三力平衡汇交定理Deduction2Principleofequilibriumofathree-forcebody06.08.202006.08.2020NanchangHangkongUniversity15A平衡时必与共线则三力必汇交O点，且共面．3F12F作用于刚体上三个相互平衡的力，若其中两个力的作用线汇交于一点，则此三力必在同一平面内，且第三个力的作用线通过汇交点。Arigidbodyissubjectedtoforcesactingatonlythreepoints.Itwillbeshownthatifthebodyisinequilibriumandtwoofthemareconcurrent,thelinesofactionofthethreeforcesmustbeconcurrent.06.08.202006.08.2020NanchangHangkongUniversity16A公理4作用和反作用定律Axiom4Lawofactionandreaction作用力和反作用力总是同时存在，同时消失，等值、反向、共线，作用在相互作用的两个物体上．Theforcesofactionandreactionmusthavethesamemagnitudeandthesamelineofactionbutoppositesense.Theforcesofactionandreactionactonvariousrigidbody.在画物体受力图时要注意此公理的应用．06.08.202006.08.2020NanchangHangkongUniversity17A公理5刚化原理Axiom5Rigidifiedprinciple变形体在某一力系作用下处于平衡，如将此变形体刚化为刚体，其平衡状态保持不变Adeformablebodyisinequilibriumactedbyaforcesystem.Theequilibriumstateofthedeformablebodywillremainunchangedifitisrigidifiedtoarigidbody.柔性体（受拉力平衡）刚化为刚体（仍平衡）D