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1、2019/1/16,Kylinsoft,Statics-1-1,ENGINEERING MECHANICS (),STATICS & MECHANICS OF MATERIALS,Pirate Captain,2019/1/16,Kylinsoft,Statics-1-2,Introduction,2019/1/16,Kylinsoft,Statics-1-3,1 What is engineering mechanics?,Engineering mechanics is the branch of physics that considers the action of forces on
2、 bodies or fluids that are both at rest and in motion; Engineering mechanics is the branch of engineering that applies the principles of mechanics to mechanical design.,2019/1/16,Kylinsoft,Statics-1-4,2019/1/16,Kylinsoft,Statics-1-5,2 Branch of Engineering Mechanics,(一). 理论力学 Theoretical Mechanics 研
3、究对象：质点 Particle、 质点系 System of Particles、 刚体 Rigid Body (1).静力学 Statics (2).运动学 Kinematics (3).动力学 Dynamics,(二). 材料力学 Mechanics of Materials 研究对象：可变形固体 Deformable Body,2019/1/16,Kylinsoft,Statics-1-6,3 Inertial reference frames,An inertial reference frame is defined to be any rigid coordinate system
4、 in which Newtons laws of particle motion relative to that frame are valid with an acceptable degree of accuracy. In most design applications used on the surface of the earth, an inertial frame can be approximated with sufficient accuracy by attaching the coordinate system to the earth.,2019/1/16,Ky
5、linsoft,Statics-1-7,4 System of units,SI Units,2019/1/16,Kylinsoft,Statics-1-8,Chapter 1 Principles of Statics,2019/1/16,Kylinsoft,Statics-1-9,1.1 Introduction to Statics,研究物体在平衡状态下的科学。即研究物体在力的作用下处于平衡状态的规律及其应用。 对象： Particle、System of Particles、Rigid Body 任务: (1) FBD(The Free-body Diagram) 物体的受力分析。 (
6、2) Reducing(Resultants) of Force systems 力系的简化(即用一简单力系代替原有力系 而不改变其对物体的作用效果)。 (3) Equilibrium Equations 力系的平衡条件。,2019/1/16,Kylinsoft,Statics-1-10,1.2 Force,Definition: Force is the name assigned to the mutual interaction between two bodies that produces the deformation of the bodies and/or affects th
7、e motion of the bodies. Contact forces arise from the direct contact between bodies and are frequently referred to simply as “pushes“ or “pulls.“ Field forces do not result from the direct contact of two bodies but are applied remotely; examples of field forces are gravitational and electromagnetic
8、forces. The unit of force in SI units is the Newton (N).,2019/1/16,Kylinsoft,Statics-1-11,静载荷（static load）与动载荷（dynamic load）,体积力（体力）与表面力（面力）,面力,体力,集中力(Concentrated Load)与分布力(Distributed Load),2019/1/16,Kylinsoft,Statics-1-12,compressing load,tension load,2019/1/16,Kylinsoft,Statics-1-13,1.3 Types of
9、 Vectors,(1) Fixed vector: a vector that has a unique point of application. (2) Sliding vector: a vector that has a unique line of action. (3) Free vector: a vector whose point of application and line of action are not unique. (Thus. a free vector is described completely by its magnitude and directi
10、on.),2019/1/16,Kylinsoft,Statics-1-14,材料力学中, 力是Fixed Vector,理论力学中, 力是Sliding Vector,2019/1/16,Kylinsoft,Statics-1-15,1.4 Principles(Axioms) of Statics,Newtons Third Law: The forces of action and reaction between bodies in contact have the same magnitude, same line of action, and opposite sense.,2019
11、/1/16,Kylinsoft,Statics-1-16,Two-force Principle(二力平衡公理): Two forces can be in equilibrium only if the case where they are equal in magnitude, opposite in direction, and collinear in action. 此公理揭示了最简单的力系平衡条件。,F1 = -F2,2019/1/16,Kylinsoft,Statics-1-17,加减平衡力系公理 : The action of a given system of forces
12、 will in no way be changed if the add to, or subtract from, these forces any other system of forces is equilibrium. 此公理是研究力系等效的重要依据。,2019/1/16,Kylinsoft,Statics-1-18,(4) Principle of Transmissibility : A force may be moved anywhere along its line of action without changing its external effect on a r
13、igid body. 当只考虑刚体受力时,作用力矢可看作Sliding Vector.,2019/1/16,Kylinsoft,Statics-1-19,(5) 刚化公理: 变形体在某一力系作用下处于平衡时，如将其刚化为刚体，其平衡状态保持不变。 刚体平衡条件是变形体平衡的必要条件而非充分条件。如右下图所示，在绳索上的作用力满足二力平衡条件绳索不一定平衡。,2019/1/16,Kylinsoft,Statics-1-20,(6) The Parallelogram Law for the Addition of Forces : Two forces acting on a particle
14、may be replaced by a single force, called their resultant, obtained by drawing the diagonal of the parallelogram which has sides equal to the given forces. 此公理给出了力系简化的基本方法. 合力的大小和方向也可通过图(b)和(c)所示的力三角形法得到。 平行四边形法则是力的合成法则, 也是力的分解法则. 例如, 拉力作用在螺钉A上(图1-5), 此力与水平方向的夹角为，按此法则可将其沿水平及铅垂方向分解为两个分力F1和F2 。,2019/1
15、/16,Kylinsoft,Statics-1-21,FR = F1 + F2,2019/1/16,Kylinsoft,Statics-1-22,帆船逆风行驶,2019/1/16,Kylinsoft,Statics-1-23,1.5 Free-body Diagram of a Body,FBD The Free-body diagram (FBD) of a body is a sketch of the body showing all forces that act on it. The term free implies that all supports have been remo
16、ved and replaced by the forces (reactions) that they exert on the body. Reactive forces(reactions): Forces that is exerted on a body by the supports to which it is attached. *Support和Constraint Applied forces: Forces acting on a body that is not provided by supports.,2019/1/16,Kylinsoft,Statics-1-24,The general procedure, A sketch of the body is drawn assuming that all supports (surfaces of contact, supporting ca
