IDEALIZATIONS OF MECHANICS
In many situations, we have to substitute the actual situation with hypothetical model which analyses the real life problems. In that case, of course, we are sure that the results of our substitutions have some reasonable correlation with reality. All analytical, physical sciences are imagined to models where their computations involve a considerable amount of imagination, ingenuity, and insight into real life situations. The following is the most fundamental idealizations of mechanics.
An object that has no size but has a mass concentrated at a point, is called a particle. In mathematical sense a particle is a body whose dimensions approach zero so that it may be analyzed as a point mass.
1.2.2 Rigid Body
A body is said to be rigid when the relative movements between its parts are negligible. Actually, every body must deform to a certain degree under the action of forces, but in many cases the deformation is negligible and may not be considered in the analysis. This rigid body concept leads to simplified computations. Refer Fig. 1.2 (a).