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Document Title
Fundamentals of Stress and Vibration Chapter Title
[A Practical guide for aspiring Designers / Analysts] 2. Engineering Mechanics
2.10 Free Body Diagram
The concept of FBD is fundamental to finding loads experienced by components in an assembly
and also their load path.
In this chapter, examples that are static and dynamic are considered. To illustrate the fundamentals,
let us begin with the concept of equilibrium.
Ø Equilibrium could be static or dynamic, wherein, the sum all forces and moments about
any point is zero.
Ø In static equilibrium, the component is at rest and may suffer elastic or plastic deformation.
Ø In dynamic equilibrium, the forces and moments are balanced in such a way that the body
has constant dynamic characteristics.
Ø In this chapter, all the bodies are considered to be absolutely rigid.
Ø The elastic deformations is sometimes represented by a linear or a torsional spring.
Example 1: find the instantaneous tension in the rope and acceleration of the bob.
[Fig 2.82: Simple pendulum]
Solution: let us write the free body diagram for the bob, as shown in [Fig 2.83]
[Fig 2.83: FBD of bob accelerating towards the mean position]
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