The conditions of equilibrium help us in finding out the reactions or forces at a particular point when the body is in equilibrium. But from a practical point of view, a body is said to be in equilibrium when it comes back to its original position after it is slightly displaced from its position of rest.
Types of Equilibrium:
In general, the following are three types of equilibrium in mechanics:
1. Stable Equilibrium:
A body is said to be in stable equilibrium if it returns to its original position after it is slightly displaced from its position of rest. This happens when some additional force sets up due to displacement and brings the body back to its original position. A smooth cylinder lying on a curved surface is in stable equilibrium. If we slightly displace the cylinder from its position of rest, it will tend to return to its original position to bring its weight normal to the horizontal axis as shown below figure:
2. Unstable Equilibrium:
A body is said to be in unstable equilibrium if it does not return to its original position, and heels farther away. After being slightly displaced from its position of rest. This happens when the additional force moves the body away from its position of rest. A smooth cylinder lying on a convex surface is in unstable equilibrium. If we slightly displace the cylinder from its position of rest. The body will tend to move away from its original position as shown in the figure:
3. Neutral Equilibrium:
A body is said to be in neutral equilibrium if it occupies a new position after being slightly displaced from its position of rest. This happens when no additional force sets up due to the displacement. A smooth cylinder lying on a horizontal plane is in neutral equilibrium as shown below figure: