Torque and Static Equilibrium Notes

Mechanical Equilibrium

• System/object is in equilibrium when net force (F_{net}) acting upon it = 0.0 N
  • Dynamic Equilibrium: System/object is in motion (velocity ≠ 0 m/s, acceleration = 0 m/s^2)
  • Static Equilibrium: System/object is not in motion (velocity = 0 m/s)

Net Force and Torque

• Net force = 0 N
  • Along x-axis = 0 N
  • Along y-axis = 0 N
  • (Along z-axis = 0 N)
• Net torque = 0 N.m
  • Sum of clockwise + anti-clockwise = 0 N.m
  • Note: Clockwise torque/moment is negative, while anti-clockwise is positive.
• Consider forces and torques along a plane (two dimensions).

Gravitational Force and Centre of Gravity

• Gravitational force: Force that objects with mass exert upon each other, always attractive.
• Gravitational force is distributed over the volume of a structure.
• Centre of gravity (cg): A single point at which the total force of gravity can be considered to act. It can be within or outside the body.
• Location of cg can be different from that of cm for the same body.