How does centre of gravity influence the equilibrium? Ok! This really makes hard to think, how does a single point determine the object's equilibrium? If an object is displaced from its equilibrium-position & if the equilibrium is stable, the object again comes back to the initial postition. My book says it is due to centre of gravity & couple constituted by the gravity & normal reaction force. But, how do this coupling and COG help in bringing back the equilibrium state? Can anyone help me visualize this??
 A: I am going to present an example which helped me understand this! 
Assume two surfaces as shown below:
Assume a droplet of water to be placed in a stable state on both of them. (i.e. at the bottom of the left one, and the top of the right one.
In the left one, if you push the water droplet by a small amount, the water droplet would tend to flow back into the point where you pushed it away from. Therefore it is in a Stable Equilibrium state. (i.e. the object comes back to its initial position.) this happens because the gravitational force always tries to bring a body to a lower potential energy position.
On the contrary, in the surface represented on the right, the slightest push would cause the droplet to go further down the surface, under gravitational acceleration. i.e. It is in an unstable equilibrium state.
Here, the gravitational force causes the droplet to return/move further away from its equilibrium state, and that is how it returns to its initial position in the left hand representation.
I hope this has been clear enough.
