The concept of the free-body diagram is summarized below.

Free-Body Diagram Summary

Four steps must be performed to construct a free-body diagram:

Determine the body or combination of bodies to be isolated.

Isolate the body or combination of bodies with a diagram that represents the complete external boundaries.

Represent all forces that act on the isolated body in their proper positions within the diagram.

Indicate the choice of coordinate axes directly on the diagram.

A free-body diagram isolates a body and illustrates all the forces that act on the body so that a complete and accurate account of all of those forces may be considered.