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Free Body Diagram

Key Concept: A free-body diagram is a drawing of a body, a part of a body, or a series

of connected bodies (isolated from its surroundings), on which all the external forces and moments acting on the body, any part of the body, or the series of bodies are shown.

In addition to external forces and moments, all dimensions, angles, and the coordinate system must be shown to complete the FBD.

In a Nut Shell: The concept of the free body diagram (FBD) is extremely important in

the study of mechanics. Use it to identify forces and moments acting on structures in

the study of statics, dynamics, solid mechanics, and fluid mechanics.

Examples of forces acting on a body include weight (due to gravity), concentrated forces, electromagnetic forces, distributed forces (such as fluid pressure acting on a submerged plate), moments, distributed moments, etc.

Consider a ladder of weight, W, resting against a smooth vertical wall, and

supported by a “rough” floor (with friction).

Click here for guidelines in constructing FBD's.

Click here for an example of the FBD of this ladder.

Click here for a detailed application involving a front end loader on a tractor.

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