For an extended object to be in equilibrium, two conditions must be satisfied: Translational equilibrium Rotational equilibrium

Static vs Dynamic Equilibrium

Static equilibrium: No linear motion and no rotational motion

Dynamic equilibrium: Constant linear velocity and/or constant angular velocity.

Stable, Unstable, and Neutral equilibrium

Stable equilibrium: the object tends to return to its equilibrium position.

Unstable equilibrium: a small displacement will cause the object to move away from its original position.

Neutral equilibrium: when we displace this object, it will simply remain in the new position.

Scalar Form

2D We have 3 Independent Equations , , and

3D We have 6 Independent Equations , , , ,

Principle of Transmissibility

If there is static equilibrium, then for any arbitrary point A we choose its moment is also 0.

Centre of Mass