Equilibrium

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

Equilibrium

– 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