Prepared By: Shakil Raiman. The turning effect of a force about a certain point is called moment (or torque) The moment can be calculate using the.

O Level Physics Chapter :05: Turning Effect of Forces

Prepared By: Shakil Raiman

5.1: Moment

The turning effect of a force about a certain point is called moment (or torque)

The moment can be calculate using the following equation.

Moment = Force × Perpendicular distance of force from "pivot“

Moment of a force = F × d

Unit: Nm

5.2: Types of Moment

There are two types of moments1. Clockwise moments2. Anticlockwise moments

5.3: Everyday Examples of Moment

5.3: Everyday Example: Consider a person trying to open a

door, by applying a force, of magnitude, F, as shown below.

The two obvious changes the person could make in order to open the door more easily arei)he/she could increase the distance "r“ii)he/she could push at 90° to the door

5.4: Principle of Moment:

In equilibrium/balanced situation,Sum of Clockwise Moments = Sum of Anticlockwise Moments

F1d1=F2d2+F3d3

5.4: Use of Principle of Moment:

5.5: Centre of Gravity:

The centre of gravity of a body is defined as the point through which its whole weight appears to act.

Centre of gravity and centre of mass is same if the object is in uniform gravitational field.

The centre of gravity of Regular Shaped Object is at the Geometrical Centre of the object.

5.5-1: Centre of Gravity of Regular Shape:

Centre of gravity of a regular shape is at its geometric centre.

For regular lamina, it is a point where it’s lines of symmetry meets.

5.5-2: Centre of Gravity of Irregular Shape :

First make three holes at three different corners of the lamina.

Hang the lamina using one hole and put a plumb line. Mark the vertical line on the lamina.

Repeat for the same for other two holes.

The three lines will meet at a point. This point is the centre of gravity of the lamina.

5.6: Stability:

Stability is the ability of an object to regain its original position after it has been displaced slightly.

There are three kinds of equilibrium: 1. Stable Equilibrium2. Unstable Equilibrium3. Neutral Equilibrium

Check the examples on the board.

5.6: Effect of Centre of Gravity on Stability:

The position of centre of gravity affects the stability of a body. In our daily life, we always need to increase the stability of different objects.

To increase the stability of an object:1. The centre of gravity should be as low

as possible.2. The base area should be as large as

possible.

Thank You All

Wish you all very good luck and excellent result.