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mechanics reduce to a rather simplified form since the geometry of the
body will not be involved in the analysis of the problem.
A rigid body can be considered as a combination of a large
number of particles in which all the particles remain at a fixed
distance from one to another, both before and after applying a load.
This model is important because the material properties of any body
that is assumed to be rigid will not have to be considered when
studying the effects of forces acting on the body. In most cases the
actual deformations occurring in structures, machines, mechanisms,
and the like are relatively small, and the rigid-body assumption is
suitable for analysis.

II STATICS

3 Force

Force is the action of one body on another. The unit of force,
called a newton (N). Experimental evidence has shown that a force is
a vector quantity since it has a specified magnitude, direction, and it
adds according to the parallelogram law. Two common problems in
statics involve either finding the resultant force, knowing its
components, or resolving a known force into two components. We
describe how each of these problems is solved using the parallelogram
law.
A vector is any physical quantity that requires both a magnitude
and a direction for its complete description. Examples of vectors
encountered in statics are force, position, and moment. A vector is
shown graphically by an arrow. The length of the arrow represents the
magnitude of the vector, and the angle between the vector and a fixed
axis defines the direction of its line of action. The head or tip of the
arrow indicates the sense of direction of the vector.
In print, vector quantities are represented by bold face letters
such as F, and its magnitude of the vector is italicized, F. For
handwritten work, it is often convenient to denote a vector quantity by

simply drawing an arrow on top of it, F .
Addition of a System of Coplanar Forces. When a force is
resolved into two components along the x and y axes, the components

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