Physics: Chapter 5 - Turning Effect of Forces

5.1 Moments
The moment of a force is the product of the force and the perpendicular distance from the pivot to the line of action of the force.

Moment of a force = Fxd
Force(perpendicular distance from pivot) = Moments

Moment = turning effect of force

5.2 Principle of Moments
When a body is in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot.

An object is said to satisfy the Principle of Moments when the force acting in clockwise motion is the same as force acting in anticlockwise motion on the same pivot.

Conditions for equilibrium:

1. All forces acting on it are balanced (Resultant force is 0)
2. The resultant moment about the pivot is 0 (Principle of Moments must apply)
   

5.3 Centre of Gravity

The centre of gravity of an object is defined as the point through which its whole weight appears to act for any orientation of the object.

The centre of gravity of a body is a single point through which its entire weight acts.

5.4 Stability
Stability refers to the ability of an object to return to its original position after it has been tilted slightly.

Three cases of equilibrium:

1. Stable equilibrium
2. Unstable equilibrium
3. Neutral equilibrium

To increase stability of an object:

1. The centre of gravity should be as low as possible
2. The area of a base should be as wide as possible