Free-Body Diagrams!

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					                     Free-Body Diagrams!
The ability to focus attention on important things is a defining
   characteristic of intelligence.
      --Robert J. Shiller, Irrational Exuberance


System: a body or group of bodies which can be isolated from all
   other bodies.

Free-body diagram: a sketch which isolates a system from its
   surroundings and shows all forces applied to it.

Boundary: an imaginary line encompassing the isolated system.

A joint is an interface between the system and the environment.
                     Free-Body Diagrams!

How to construct a FBD step-by-step (do these steps every time).

1. Decide which body or system of bodies to isolate.

2. Choose the boundary.

3. Apply all forces which act on the body.

4. Indicate coordinate axes.
                      Free-Body Diagrams!

Rule of Joint Resistance

    If a joint isolated from the system could resist a translational
displacement along or rotational displacement about a certain axis,
then a corresponding force or moment must be represented on the
free-body diagram.

Everyday examples.
Free-Body Diagrams!
Free-Body Diagrams!
Free-Body Diagrams!
Free-Body Diagrams!
Free-Body Diagrams!
Free-Body Diagrams!