《理论力学》双语教学第一章静力学基本公理和物体的受力分析.ppt

1,,Part 1 Statics,2,,第一篇 《静力学》,,3,,4,It mainly studies simplifications and equilibrium conditions of force systems and applications of the corresponding results. 静力学主要研究：力系的简化和力系的平衡条件及其应用5,,Chapter 1 Fundamental principles of statics and force analysis,,6,,第一章 静力学基本公理和物体的受力分析,,7,§1–1 Fundamental concepts in static§1–1 静力学的基本概念§1–2 Principles of static§1–2 静力学公理,,,,8,§1–3 Constraints and their reaction forces §1–3 约束与约束反力 §1–4 Force analysis and force diagrams §1–4 物体的受力分析与受力图,,,,9,,Chapter 1: Fundamental principles of static and force analysis,,,第一章 静力学基本公理和物体的受力分析,10,,,,2)Effects of forces: ①motion (external effect)②deformation (internal effect). 2. 力的效应： ①运动效应(外效应) ②变形效应(内效应)。

11,,,,,12,,,,,13,,,,,,,14,,,,公理1 二力平衡公理,,,,1st Principle: two force equilibrium,A rigid body subjected to the action of two forces can be in equilibrium, the necessary and sufficient conditions are: 作用于刚体上的两个力，使刚体平衡的必要与充分条件是：the two forces are equal in magnitude, | F1 | = | F2 | 这两个力大小相等 | F1 | = | F2 | the two forces are opposite in direction, F1 = –F2 方向相反 F1 = –F2 the two forces are collinear, 作用线共线， the two forces act on the same body.作用于同一个物体上15,,,,Explanation: 说明：①As far as rigid bodies are concerned, the conditions above are necessary and sufficient. ①对刚体来说，上面的条件是充要的 ②As far as deformable bodies are concerned, the conditions above are only necessary. ②对变形体来说，上面的条件只是必要条件(或多体中),16,,,,17,,,,,18,,,,,,,19,,,,,20,,,,,21,,,,[证] ∵ 为平衡力系，∴ 也为平衡力系。

又∵ 二力平衡必等值、反向、共线，∴ 三力 必汇交，且共面22,,,,,23,,,,,24,,,,公理5告诉我们：处于平衡状态的变形体，可用刚体静力学的平衡理论25,,,,,26,,,Reaction force of a constraint: The force by which a constraint acts on a body, therebyrestricting its displacements, is called the force ofreaction of the constraint. 约束反力：约束给被约束物体的力叫约束反力Constraint: Anything that restricts the displacement of a givenbody in space. (here, constraint is a noun, not a verb). 约束：对非自由体的某些位移预先施加的限制条件称为约束这里，约束是名词，而不是动词的约束27,,,①their magnitude is usually unknown; ①大小常常是未知的； ②their direction is always opposite to the direction in which the given constraint prevents the displacement of the body; ②方向总是与约束限制的物体的位移方向相反；,,,28,,,③the point of application is the contact point between the body and the constraint. ③作用点在物体与约束相接触的那一点。

G,29,,,,30,,,,31,,,,,32,,,,,33,,,,,Pin,34,,,,,35,,,,A,36,,,,,Pin,37,,,,38,,,,39,,,,40,,,,41,,,,42,,,,43,,,,44,,,,45,,,,46,,,,47,,,,,,48,,,,,1. Force analysis To solve a problem of static. First select the body to be studied. 一、受力分析解决力学问题时，首先要选定需要进行研究的物体，即选择研究对象；,49,,Secondly, in accordance with the given conditions and constraints, analyze the forces which act on the bodies using the basic concepts and principles. This process is called force analysis. 然后根据已知条件，约束类型并结合基本概念和公理分析它的受力情况，这个过程称为物体的受力分析。

50,,The forces acting on a body can be classified as: 作用在物体上的力有：1: active forces, such as the gravitational force, the force of wind power, the pressure of gases, etc. 一类是:主动力,如重力,风力,气体压力等2: passive forces, such as reaction force of constraints 二类是：被动力，即约束反力51,,The main steps to draw the force diagrams: 画物体受力图主要步骤为：①select the object under study;①选研究对象；②divide the object into several parts and study the partsone by one;②取分离体； ③draw the active forces;③画上主动力；④draw the reaction force of the constraints. ④画出约束反力。

52,,,,53,,,,,54,,,,,Rod,55,,,,56,,,,57,,,,58,,,,59,,,,,,60,,,,,,61,,,,,,62,,,,,,63,,,,,,64,,,,,,65,,,,66,,,,67,,,,68,,,,please give attention to the direction of the forces. If the direction of the action force has been determined, the direction of the reaction force is opposite to the action force. Don’t draw the direction of forces wrong. 要注意，作用力的方向一旦确定，反作用力的方向一定要与之相反，不要把箭头方向画错69,,,,70,,,,71,,,,The end,,Statics,72,静力学,,,,本章结束,,。