The topic of statics deal with objects or structures which are in equilibrium, that is
structures that are at rest or in uniform, (non-accelerated) motion. We will be normally
looking at structures which are at rest. For these structures we will be interested in
determining the forces (loads and support reactions) acting on the structure and forces
acting within members of the structure (internal forces). To determine forces on and in
structures we will proceed carefully, using a well defined methodology. This is important
as most problems in statics and strength of materials are not the kind of problem in which
we can easily see the answer, but rather we must relay on our problem solving techniques.
For static equilibrium problems, we will be able to apply the Conditions
of Equilibrium to help us solve for the force in
and on the structures. There are two general equilibrium conditions: Translational Equilibrium, and Rotational
Equilibrium.
The Translational Equilibrium condition states that for an object or a structure
to be in translational equilibrium (which means that the structure as a whole will not
experience linear acceleration) the vector sum of all the external forces acting on the
structure must be zero. Mathematically this may be expressed as:
or, in 3-dimensions:
, 
, 
That is, forces in the x-direction must sum to zero, for translational equilibrium in the
x-direction, and, the forces in the y-direction must sum to zero, for translational
equilibrium in the y-direction, and, the forces in the z-direction must sum to zero, for
translational equilibrium in the z-direction.
To see the application of the first condition of equilibrium and also the application
of a standard problem solving technique, let's look carefully at introductory examples. Select: Example 1- Concurrent
Forces.
Select: Example 2- Concurrent Forces
Select:
Topic 1: Statics I - Principles Table of Contents
Statics & Srength of
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