Equilibrium Of A Rigid Body Moments And Center Of Gravity
Equilibrium of a rigid body, moments, and center of gravity
Equilibrium Conditions
 For an object to be in equilibrium, the net force and net torque acting on it must be equal to zero.
Center of Gravity (CG)
 The center of gravity (CG) of an object is the point where the entire weight of the object is considered to be concentrated.
For a symmetric object, the CG is at its geometric center.
 The CG of a system of particles is the point where the total torque due to the weights of the particles is zero.
Methods for finding the CG

For symmetric objects: the CG can be determined by inspection.

For objects with simple shapes: the CG can be calculated using formulas.

For irregular objects: the CG can be determined by the principle of moments.
Stability

A body is in stable equilibrium if, when slightly disturbed from its equilibrium position, it tends to return to that position.

A body is in unstable equilibrium if, when slightly disturbed from its equilibrium position, it tends to move away from that position.

The stability of a body depends on the position of its CG.
An object is most stable when its CG is lowest.