SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/eng-free-body-diagram

What does a free-body diagram show?

One isolated body and every force acting ON it, not the forces it exerts on others.

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  1. All forces in the whole system at once
  2. The forces the body pushes onto its supports
  3. One isolated body and the forces acting on it ✔

Why: You cut the body free, replace each support or contact with the force it applies, and draw those. Forces the body exerts on other things belong on those other bodies' diagrams.

Huh, didn't know that: Engineers start almost every statics problem with a free-body diagram before writing any equation.

The dad joke
I drew a free-body diagram of myself on Monday. Every arrow pointed back to bed.
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References

Answer: One isolated body and the forces acting on it. You cut the body free, replace each support or contact with the force it applies, and draw those. Forces the body exerts on other things belong on those other bodies' diagrams.

  1. Engineering Statics (Baker and Haynes): 1.1 Newton's Laws of Motion engineeringstatics.org/newtons-laws.html
    isolate a body or system of interest and identify the forces acting on it, while ignoring any forces exerted by it
    Checked 2026-10-10.

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EngineeringOne newton of force equals which combination of SI base units?EngineeringFor an object at rest, Newton's second law F = ma becomes what?EngineeringA force's line of action passes right through the pivot. What moment does it make about that pivot?

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