What is a free body diagram?

A free body diagram is a graphical illustration used in physics and engineering to visualize applied forces, moments, and reactions acting on a body. It depicts a single body or connected bodies isolated from their surroundings to simplify the analysis of mechanical systems. Sometimes, forces within the diagram are arranged as a polygon of forces to calculate a resultant force graphically.

What we know

• A free body diagram is a graphical illustration used to visualize applied forces, moments, and resulting reactions on a free body in a given condition. [1, 2]
• The diagram depicts a body or connected bodies, which may consist of multiple internal members like a truss or a compact body like a beam. [2]
• Applied forces can sometimes be arranged as the edges of a polygon of forces in order to calculate the resultant force graphically. [2]

Where to go next

• compared withHow do kinematic diagrams differ from force diagrams?
• the bigger pictureHow are external forces handled in rigid body dynamics?
• how it workedHow do you construct a force polygon to find a resultant force?
• a case in pointWhat role do free body diagrams play in solving complex engineering problems?
• whenWhat are the historical origins of using force diagrams in classical mechanics?
• an unexpected connectionHow do particle physicists use diagrams similar to mechanical force sketches?Just as a free body diagram graphically represents physical forces acting on a macroscopic body, a Feynman diagram graphically represents the mathematical expressions and interactions of subatomic particles.

Sources

• [1]free body diagram (Wikidata Q968841) · CC0 1.0
• [2]Free body diagram · CC BY-SA 4.0
• [3]Kinematic diagram · CC BY-SA 4.0
• [4]Rigid body dynamics · CC BY-SA 4.0
• [5]Feynman diagram · CC BY-SA 4.0