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Statics For Dummies by James H. Allen, III, PE, PhD

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Chapter 14. The F.B.D.: Knowing What to Draw and How to Draw It

A free-body diagram (F.B.D.) is the physical representation of an object (or part of an object) with all actions acting on it. In statics, this setup usually includes forces such as concentrated and distributed loads, support reactions, internal forces, and self weight; check out Chapter 13 for more on these force categories. These four categories of forces help depict all forces on a given object (although in non-statics problems, you may include other vector actions such as velocities, accelerations, distances, and many others). Consider an 8,000-pound elephant and an 8,000-pound commercial vehicle. Both have the same self weight (force due to gravitational effects on their masses), but the location of that weight tremendously affects the objects they're resting on in drastically different ways.

In this chapter, I show you some of the situations you need to be mindful of when tackling any statics analysis problem with an F.B.D. I start with a basic list of items you want to be sure to include on your free-body diagram. I also show you how you can extract additional free-body diagrams from within a given F.B.D.

Getting Your F.B.D. Started

The old saying that a picture is worth a thousand words may seem clichéd at first, but this simple statement accurately emphasizes the importance of a well-constructed ...

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