Lesson 5, Topic 4
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# Types of Equilibrium

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There are three types of equilibrium namely:

1. Stable
2. Unstable
3. Neutral

### (1) Stable Equilibrium:

A body is said to be in stable equilibrium if when slightly displaced or tilted and released, it returns to its original position. For example, a ball kept at the bottom of a hemisphere, if slightly displaced the ball will return to its original position.

For stable equilibrium, the conditions are:

(i) A body must have a low centre of gravity.
(ii) The vertical line through the centre of gravity must fall within the base even if slightly tilted.
(iii) The height of the centre of gravity must increase from the base as the body is slightly tilted.

### (2) Unstable Equilibrium:

A body is said to be in unstable equilibrium if when slightly displaced and released, it tends to move further away from its original position. Consider a ball kept at the top of a sphere. If we slide it, the ball tends to roll away from the topmost point.

Conditions for unstable equilibrium are:

(i) High Centre of gravity.
(ii) Narrow base.
(iii) Low P.E due to decrease in height of Centre of gravity when slightly tilted.

### (3) Neutral Equilibrium:

A body is said to experience neutral equilibrium if when slightly displaced or tilted, it tends to come to rest in its new position. For example, displace a ball kept on a horizontal surface slightly.

Evaluation Questions:

1. What is a couple?

2. State the conditions of equilibrium under the action of parallel coplanar forces.

3. Define
(i) Centre of gravity of a body
(ii) Centre of mass of a body

4. State the types of equilibrium you know.

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