工程力学双语课件ch02-Resultant-of-Concurrent-Forces-in-a-Plane

1、Chapter 2 Resultant of Concurrent Forces in a Plane,Wang Ming-lu,Resultant: 组合的，合成的 Concurrent:共点的，汇交的 Coplanar：共面的 Vector:矢量, 向量 Parallelogram:平行四边形 Triangular:三角形的 Trigonometric function：三角函数 Polygon：多边形,Specialized Vocabulary,Magnitude：量值，大小 Component：部件，分量 Rectangular：矩形的, 长方形的; 直角的 Horizontal：水

2、平的 Vertical：垂直的; 铅垂的,Specialized Vocabulary,Chapter Objectives.,1. Depict the graphical representation of a force vector. 2. Explain the Parallelogram method and triangular method for adding vectors to find their resultant. 3. Determine the components of a vector along any specified pair of axes. 4.

3、 Use graphical techniques and the trigonometry of oblique triangles to add two or more vectors.,Chapter Objectives.,5. Compute the rectangular components of a force. 6. Use the method of rectangular components to find the resultant of two or more vectors. 7. Apply the concept of a negative force to

4、the subtraction of vectors.,2.1 Introduction.,Force system： A group of forces which act on the same body,Force system,coplanar force system,Non-coplanar force system,concurrent force system,parallel force system,general case force system,concurrent force system,parallel force system,general case for

5、ce system,Force system：concurrent force system 汇交力系,A force system is said to be concurrent （汇交） if the action lines of all the forces intersect in a common point.,coplanar,Non-coplanar,2.1 Introduction.,2.1 Introduction.,Force system：Parallel force system 平行力系,A parallel force system is one in whic

6、h the action lines of the forces are parallel.,2.1 Introduction.,Force system：General case force system 一般力系,2.1 Introduction.,Equilibrium (平衡)： If a force system applied to a body produces no external effect on the body, the forces are said to be in equilibrium,2.1 Introduction.,Force system in equ

7、ilibrium (平衡力系)： If the effects of every force in a force system can be counteracted, so that the particle or the rigid body can be kept in the equilibrium status or without changing its motion status, the Force system is in equilibrium.,Equilibrant (平衡力)： Relative to the other forces in the same fo

8、rce system in Equilibrium, each force can be called equilibrant,2.1 Introduction.,Force system in equilibrium (平衡力系)：,2.1 Introduction.,Equivalent Force System (等效力系)：,Definition: Two force systems that produce the same external effects on a rigid body are said to be equivalent. Resultant Force （合力）

9、 If a force is equivalent to a force system, this force can be considered as the Resultant Force of this force system Component force（分力） Each force which is composing the resultant force can be considered as the Component Force,2.2 Graphical representation of force: vector.,1. About Scalar Quantiti

10、es and Vector Quantities. 2. About the Represent of Vector in Print and longhand.,2.3 Resultant of two concurrent forces.,2.3.1 Parallelogram method.,2.3 Resultant of two concurrent forces.,2.3.2 Triangular method.,2.3 Resultant of two concurrent forces.,Example 2.1 (P44).,Example 2.1 (P44).,2.3 Res

11、ultant of two concurrent forces.,2.3 Resultant of two concurrent forces.,Example 2.2 (P45).,2.3 Resultant of two concurrent forces.,Example 2.3 (P46).,2.3 Resultant of two concurrent forces.,Example 2.3 (P46).,2.3 Resultant of two concurrent forces.,Example 2.4 (P47).,2.3 Resultant of two concurrent

12、 forces.,2.3.4 Problems. Do the problems 2.1-2.10 by yourself, and then I will tell you the answers of them.,2.4 Resultant of three or more concurrent forces.,2.4 Resultant of three or more concurrent forces.,A,B,C,D,2.4 Resultant of three or more concurrent forces.,Example 2.5 (P50).,2.4 Resultant

13、of three or more concurrent forces.,Problems. Do the problems 2.11-2.14 by yourself, and then I will tell you the answers of them.,2.5 Components of a force vector.,2.5.1 About Components 2.5.2 About rectangular Components,Example 2.6 (P53).,2.5 Components of a force vector.,Example 2.7 (P54).,2.5 C

14、omponents of a force vector.,Problems. Do the problems 2.15-2.20 by yourself, and then I will tell you the answers of them.,2.5 Components of a force vector.,2.6 Resultant of concurrent forces by rectangular components.,2.6.1 Method of rectangular components.,The magnitude of the resultant force pro

15、jection to an axis equals the algebraic sum of all the component forces projection to the same axis,2.6.1 Method of rectangular components.,2.6 Resultant of concurrent forces by rectangular components.,2.6 Resultant of concurrent forces by rectangular components.,Example 2.8 (P58).,2.6 Resultant of concurrent forces by rectangular components.,Example 2.9 (P59).,2.6 Resultant of concurrent forces by rectangular components.,Example 2.10 (P61).,2.7 Difference of two forces: Vector differences.,1. About negative force. 2. About vector differences.,2.7.2 Example. Example 2.11 (P62).,2.7 Diff