There are 3 types of equilibrium (for objects whose positions of C.G. are higher than pivot): stable equilibrium, unstable and neutral equilibrium.

Stable Equilibrium

When object is slightly displaced:

• The C.G. of the object is raised from G₁ to G₂.
• Its weight has a moment about the pivot that causes the object to rotate back (return) to its original position.
• The line of action of the weight acts within the base.

Unstable Equilibrium

When object is slightly displaced:

• The C.G. of the object is lowered from G₁ to G₂.
• Its weight has a moment about the pivot that causes the object to topple into a new position.
• The line of action of the weight acts outside the base.

Neutral Equilibrium

When object is slightly displaced:

• The C.G. of the object remains at the same horizontal level.
• Its weight has zero moment about the pivot and will not cause it to topple.

 

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