TAILIEUCHUNG - Ebook Engineering mechanics statics: Part 2
(BQ) Part 2 book "Engineering mechanics statics" has contents: Method of joints, method of sections, frames and machines, centers of mass and centroids, special topics, frictional phenomena, applications of friction, potential energyand stability,. and other contents. | Chapter DISTRIBUTED FORCES CHAPTER OUTLINE 5/1 Introduction SECTION A. Centers of Mass and Centroids 5/2 Center of Mass 5/3 Centroids of Lines, Areas. and Volumes 5/4 Composite Bodies and Figures; Approximations 5/5 Theorems of Pappus SECTION 8. Special Topics 5/6 Beams-External Effects 5/7 Beams-Internal Effects 5/8 Flexible Cables 5/9 Fluid Statics Chapter Review 5/1 INTRODUCTION In the pr evious chapte rs we treated a ll forces as concentr ated along t heir lin es of action and at thei r points of applicat ion. This treatment provided a r eason able model for tho se for ces. Act ually, " concentrated" forces do not exist in the exact se nse , since eve ry exte r na l for ce applied mechanically to a body is distributed over a finite contact area , however sma ll. The force exerted by th e pavem ent on an automobile tire, for instance, is ap plied t o the tire over it s entire area of contact, Fig. 5/ 10, which may be appre ciable if th e tire is soft . When analyzing t he for ces act ing on t he car as a whole, if the dim ension b of the contact area is negligible compared with the other pert inent dim en sion s, such as the distan ce between wheels, then we may replace the actual distr ibuted contact for ces by t heir resu ltant R treated as a concentrated for ce. Even th e for ce of contact between a hardened steel ba ll a nd it s race in a loaded ball bea rin g, Fig. 5/ 16, is applied over a finit e tho ugh ext remely small contact area. The forces applied to a two-force memb er of a truss, Fig. Marwan and Waseem AI-Iraqi 225 226 Chapter 5 Di st ributed For ces O R o (a) Enla rged view orconta ct I I R R Ib' C I I I liNII c ~ I I C lei Figure 5 '1 Marwan and Waseem AI-Iraqi 5/ 1c, are applied over a n actual area of contact of the pin against the hole and internally acro ss the cut section as shown. In these and othe r similar examples we may treat the forces as concentrated when analyzing their external effects
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