To draw free body diagrams

  • Isolate body of interest
  • Identify all forces acting on that body only
  • Draw vector representing each force
  • RESOLVE into x and y components if necessary


– Resultant force on object must be zero

  •  Translational equilibrium
  •  Linear acceleration of object is zero
  •  Resultant force = 0

– Resultant torque on object about any axis must be zero

  •  Rotational equilibrium
  •  Sum of clockwise moments about any axis of rotation = sum of the anticlockwise moments about the same axis. Axis can be lying on any part of the object. (Principle of moments)
  •  Angular acceleration of object is zero
  •  Lines of action of all forces acting on the object intersect at a point


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