In the preceding chapter it was assumed that each of the bodies considered
could be treated as a single particle. Such a view, however, is
not always possible, and a body, in general, should be treated as a combination
of a large number of particles. The size of the body will have
to be taken into consideration, as well as the fact that forces will act on
different particles and thus will have different points of application.
Most of the bodies considered in elementary mechanics are
assumed to be rigid, a rigid body being defined as one which does
not deform. Actual structures and machines, however, are never
absolutely rigid and deform under the loads to which they are subjected.
But these deformations are usually small and do not appreciably
affect the conditions of equilibrium or motion of the structure
under consideration. They are important, though, as far as the resistance
of the structure to failure is concerned and are considered in
the study of mechanics of materials.
In this chapter you will study the effect of forces exerted on a
rigid body, and you will learn how to replace a given system of forces
by a simpler equivalent system. This analysis will rest on the fundamental
assumption that the effect of a given force on a rigid body
remains unchanged if that force is moved along its line of action ( principle
of transmissibility ). It follows that forces acting on a rigid body
can be represented by sliding vectors, as indicated earlier in Sec. 2.3.
Two important concepts associated with the effect of a force
on a rigid body are the moment of a force about a point (Sec. 3.6)
and the moment of a force about an axis (Sec. 3.11). Since the determination
of these quantities involves the computation of vector products
and scalar products of two vectors, the fundamentals of vector
algebra will be introduced in this chapter and applied to the solution
of problems involving forces acting on rigid bodies.
Another concept introduced in this chapter is that of a couple,
i.e., the combination of two forces which have the same magnitude,
parallel lines of action, and opposite sense (Sec. 3.12). As you will
see, any system of forces acting on a rigid body can be replaced by
an equivalent system consisting of one force acting at a given point
and one couple. This basic system is called a force-couple
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
الرجوع الى لوحة التحكم
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