工程力学双语课件ch04-Resultant-of-non-concurrent-Forces-in-a-Plane

1、Chapter 4 Resultant of non-concurrent Forces in a Plane,Wang Ming-lu,Specialized Vocabulary,Rigid body：刚体 Transmissibility：可传递性 Moment：力弯, 挠, 磁矩, 转矩 Parallel force：平行力系 Couple：力偶，电偶， 热偶 Arm of the couple：力偶臂 Distributed loading：分布载荷 Uniform load：均布载荷 Triangular load：三角载荷 Geometric center：几何中心,Chapte

2、r Objectives.,1. Compute the moment about any selected point, using either the definition of moment or Varignons theorem. 2. Find the magnitude and location of the resultant for a system of parallel or nonparallel forces. 3. Describe the combination of forces that form a couple and define the moment

3、 of a couple. 4. Resolve a given force into an equivalent force-couple combination. 5. Determine the magnitude and location of the resultant for both uniform and triangular distributed loads.,4.1 Introduction.,About a rigid body.,Rigid body：shape and size will never change ( idealized model ),1. Rig

4、id body is a special system of particles, the distance between any two particles will not change .,directions：,2. All rules of system of particles can be applied to rigid body with a simpler form.,4.2 Transmissibility,A force may be transmitted or moved to any other point on its line of action witho

5、ut changing the effect of the force on the rigid body.,1、The body must be rigid body, and not be deformable body.,2、The rigid body must be one only, and not be two or more.,Q：whats the limitations of the principle of transmissibility ？,4.2 Transmissibility,4.3 Moment of a force.,4.3.1 definition of

6、moment of a force.,direction of moment .,4.3 Moment of a force., is scalar quantity。,(2) When F=0 or d=0, =0。,(3) =2AOB=Fd 。,4.3.2 Noting of moment of a force.,4.4 Theorem of moment.,4.4.1. Varignons theorem The moment of a force about a point is equal to the sum of the moment of the components of t

7、hat force about the same point.,4.4.2 Example. Example 4.1 (P101). Example 4.2 (P102). Example 4.3 (P104).,4.4 Theorem of moment.,4.4.3 Problems. Do the problems 4.1-3.7 by yourself, and then I will tell you the answers of them.,4.4 Theorem of moment.,4.5 Resultant of parallel forces.,4.5.2 Example.

8、 Example 4.4 (P108). 4.5.3 Problems. Do the problems 4.8-4.11 by yourself, and then I will tell you the answers of them.,4.5 Resultant of parallel forces.,4.6 Resultant of nonparallel forces.,Resultant of nonparallel forces have the same way as Resultant of parallel forces by resolving each force in

9、to rectangular components.,4.6.2 Example. Example 4.5 (P110). 4.6.3 Problems. Do the problems 4.12-4.19 by yourself, and then I will tell you the answers of them.,4.6 Resultant of nonparallel forces.,4.7 Moment of couple,Definition of moment of couple.,4.7 Moment of couple,4.7 Moment of couple,4.7 M

10、oment of couple,两个推论：,two corollaries:,4.7 Moment of couple,The composition and the equilibrium of a coplanar system of force couples平面力偶系的合成与平衡,4.7 Moment of couple,d,d,Therefore the total moment of the resultant force couples is,4.7 Moment of couple,4.7 Moment of couple,4.7 Moment of couple,Exampl

11、e A workpiece lies on a drill press, four equidimensional holes are drilled in the work piece, the force couple of every drill is . Determine the total moment of the resultant of the force couples and the horizontal reaction forces at point A and B.,例 在一钻床上水平放置工件,在工件上同时钻四个等直径的孔,每个钻头的力偶矩为 求工件的总切削力偶矩和A 、B 端水平反力?,4.7 Moment of couple,4.7 Moment of couple,4.8 Resolution of a force into a force and couple.,可以把作用在刚体上点A的