tailieunhanh - Ebook Engineering mechanics (Volume 1: Statics - 7th edition): Part 2
(BQ) Part 2 book "Engineering mechanics (Volume 1: Statics)" has contents: Distributed forces (centers of mass and centroids, special topics), friction (frictional phenomena, applications of friction in machines), virtual work. | 5 Distributed Forces CHAPTER OUTLINE 5/1 Introduction Section B Special Topics Section A Centers of Mass and Centroids 5/6 Beams—External Effects 5/2 Center of Mass 5/7 Beams—Internal Effects 5/3 Centroids of Lines, Areas, and Volumes 5/8 Flexible Cables 5/4 Composite Bodies and Figures; Approximations 5/9 Fluid Statics 5/5 Theorems of Pappus 5/10 Chapter Review 5/1 Introduction In the previous chapters we treated all forces as concentrated along their lines of action and at their points of application. This treatment provided a reasonable model for those forces. Actually, “concentrated” forces do not exist in the exact sense, since every external force applied mechanically to a body is distributed over a finite contact area, however small. The force exerted by the pavement on an automobile tire, for instance, is applied to the tire over its entire area of contact, Fig. 5/1a, which may be appreciable if the tire is soft. When analyzing the forces acting on the car as a whole, if the dimension b of the contact area is negligible compared with the other pertinent dimensions, such as the distance between wheels, then we may replace the actual distributed contact forces by their resultant R treated as a concentrated force. Even the force of contact between a hardened steel ball and its race in a loaded ball bearing, Fig. 5/1b, is applied over a finite though extremely small contact area. The forces applied to a two-force member of a truss, Fig. 5/1c, are applied over an actual area of contact of the pin against the hole and internally across the cut section as shown. In these and other similar examples we may treat the forces as concentrated when analyzing their external effects on bodies as a whole. 233 234 Chapter 5 Distributed Forces b R (a) Enlarged view of contact R (b) R C C (b) C C (c) Figure 5/1 If, on the other hand, we want to find the distribution of internal forces in the material of the body near the contact location, where .
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