《静力学基本公理和物体的受力分析1》由会员分享，可在线阅读，更多相关《静力学基本公理和物体的受力分析1（42页珍藏版）》请在金锄头文库上搜索。
1、1,Chapter 1 Exordium,工 程 力 学,engineering mechanics,第二章 静力学基本公理和物体的受力分析,2,静力学的基本概念和受力分析 the basic concepts of static and the analysis of all forces which act on the body,21 静力学的基本概念 the concepts of principle of statics,22 静力学公理 the laws of static,23 约束与约束反力 constraint and constraint force,24 物体的受力分析与
2、受力图 the free body diagrams of a single body and system of bodies,3,In this chapter we will introduce the basic Concepts of static and the statements of general static principles. To introduce the Concepts of the constraint forces and discuss how to draw the freebody diagram for a body.,本章目标,Chapter
3、objectives,静力学模型 Static models:,（1） 物体的合理抽象与简化 the reasonable reduction and abstract of the body,（2） 受力的合理抽象与简化 the reasonable reduction and abstract of loadings,（3）接触与连接方式的合理抽象与简化 the reasonable reduction and abstract of contact and joined manners,4,5,力是物体间相互的机械作用，它具有两种效应；一是使物体的运动状态发生 改变，二是使物体产生变形。
4、前者称为力的外效应。后者称为力的内效应。,力的概念 the concept of force,The force is mechanical actions between one and another body ,it has two effects, one is motion effect ,that it will tend to change the bodys state of motion, the other is deformation effect, that it will tend to change the bodys shape and size.,力的三要素 ：
5、 three elements of force,力是一个矢量，具有大小方向和作用点三个要素，常用一个带箭头的有方向线段表示力矢量。,Force is a vector, that is represented graphically by an arrow, which is used to define its magnitude, direction, and sense.,The magnitude of the vector is the length of the arrow, the direction is defined by the angle between refere
6、nce axis and the arrows line of action, and the sense is indicated by the arrowhead.,力的单位 ：units of force,N or KN,6,力系的概念 The concepts of force systems,作用于物体上的一群力,The sum of all loadings acted on the body,平衡力系 equilibrium force systems,物体在力系作用下处于平衡，我们称这个力系为平衡力系。,A body subjected a force system is eq
7、uilibrium ,then the force system is called equilibrium force systems,平面力系 force system in a plane.,All forces subjected to the body are the same plane,空间力系 dimensional force system,All forces subjected to the body are different planes,7,平面汇交力系,the current force system in a plane.,所有力的作用线汇交于一点的平面力系,A
8、ll the forces in a plane act at a point.,平面平行力系,The parallel force system in a plane,所有力的作用线都互相平行,All forces are parallel in a plane .,平面任意力系 Arbitrary force system in a plane,所有力的作用线任意分布在一个平面内,All the forces distributed arbitrary in a plane.,8,It is ideal model of body it can be considered as a com
9、bination of a large number of particles in which all the particles remain at a fined distance from one another both before and after applying a load,刚体 Rigid-body,就是在力的作用下，大小和形状都不变的物体。 there is no deformation whenever a body subjected to any forces .,刚体是物体的理想化模型,平衡equilibrium,是指物体相对于惯性参考系保持静止或作匀速直线运
10、动的状态。,A body is in equilibrium provided it is at rest if originally at rest or has a constant velocity if originally in motion.,质点 particle,是指具有一定质量而形状与大小可以忽略不计的物体。 A particle has a mass ,but a size that can be neglected.,9,静力学公理the laws of static,A body is equilibrium due to subjected two forces, t
11、he necessary and sufficient conditions is that the two forces has the same magnitude , opposite and collinear.,应用 applying,Construct equilibrium conditions,建立平衡条件的,10,说明：对刚体来说，上面的条件是充要的 Illustrate :the condition mentioned is sufficient and necessary for bodies.,对变形体(或多体中)来说，上面的条件只是必要条件 The condition
12、 mentioned is necessary for deformation Body,but not sufficient .,11,二力杆：members subjected to two forces.,二力杆,只在两个力作用下平衡的刚体叫二力杆。 Only subjected to two forces, they have the same magnitude, opposite direction and collinear.,12,在已知力系上加上或减去任意一个平衡力系，并不 改变原力系对刚体的作用。,公理2 加减平衡力系原理 Addition and reduction eq
13、uilibrium force systems law,We can add or reduce equilibrium force systems at a body. The effect of the force system must Be the same as before.,应用 applying,简化力系,Deduct the force systems,13,推论1：力的可传性。 Principle of transmissibility of a force.,因此，对刚体来说，力作用三要素为：大小，方向，作用线,作用于刚体上的力可沿其作用线移到同一刚体内的任一点， 而不改
14、变该力对刚体的效应。,the force can transmit along with its action line, the effect of the force must be the same as before transmitting.,It states, the elements of a force are magnitude, direction and line of action. the vector of a force is a sliding vector.,A,B,F,F,A,B,B,A,F1,F2,F2=F=-F1,F2,令F=F1=F2,14,公理3
15、力的平行四边形法则 parallelogram law,作用于物体上同一点的两个力可合成一个合力，此合力也作用于该点，合力 的大小和方向由以原两力矢为邻边所构成的平行四边形的对角线来表示。,Make a sketch showing the vector addition using the parallelogram law. Two “component” forces add according to the parallelogram law. Yielding a resultant force that forms the diagonal of the parallelogram
16、,A,F1,F2,R,A,F1,F2,R,15,If a force is to be resolved components along two axes directed form the tail of the force,then start at the head of the force and construct lines parallel to the axes, thereby forming the parallelogram. The sides of the parallelogram represent the components. Label all the know and unknown force magnitudes and the angles on the sketch and identify the two unknowns.,Redraw a half portion of the parallelogra
