《理论力学》双语教学 第五章 空间力系(130P).pptVIP

1 解：①选研究对象 ②作受力图 ③选坐标列方程 最好使每一个方程有一个未知数，方便求解。 Solution: ①select the object under study ②draw the force diagram ③select a coordinate system and write out the equations. If there is only one unknown quantity in every equation, it is easy to get the solution. Method 2: Project the force system in space on the three axes, change the problem into that of a force system in a plane, and solve it. Please, practice it by yourselves after the class. 方法(二) :将空间力系投影到三个坐标平面内，转化为平面力系平衡问题来求解，请同学们课后自己练习求解。 1. Concepts and content: 一、概念及内容： 1)The force couple or the moment of a force about a point is a vector. 1、空间力偶及空间力对点之矩是矢量， 2)The moment of force about an axis, a force couple in plane and the moment of a force in plane about a point are algebraic quantities. 2、空间力对轴之矩和平面力偶、平面力对点之矩是代数量。 Exercises to chapter 5 the force system in space 第五章 《空间力系》习题课 3)The law of projection of the resultant force of a force system in space is 3、空间力系合力投影定理： 4)The law of the resultant moment of the force system in space is 4、空间力系的合力矩定理： 5)The relationship between the moment of the force about a point and the moment of a force about an axis which passes the point is 5、空间力对点之矩与对轴之矩的关系： 2. Basic Equations 1) The equilibrium equations of a force system in space are 二、基本方程 1、空间力系的平衡方程 A general force system in space 空间一般力系 Concur--rent force system in space 空间汇交力系 System of force couples in space 空间力偶系 四矩式、 五矩式和六矩式的附加条件均 为使方程式独立。 The additional conditions of the equations of four moments, the equations of five moments and the equations of six moments make the equations independent. 空间∥x轴力系 Force system in space on x axis only 空间∥xoy 面的力系 Force system in space on xoy plane only 2) Some problems about the force systems in space: ①x , y, z may not be the three axes of the moment. We can select six axes arbitrarily. ②The equations for the moments can be less than three (because MO is a vector). ③There are