Keshu

1. Principle of Moments

The Principle of Moments is a rule in physics that explains when an object will balance or rotate.

Statement (simple):

Key ideas you must know first:

• Force → a push or pull

• Pivot (or fulcrum) → the point about which an object turns

• Moment → the turning effect of a force

Formula:

Moment=Force x Perpendicular distance from pivot

So:

• Bigger force → bigger turning effect

• Bigger distance from pivot → bigger turning effect

2. Balancing Using the Principle of Moments

An object is balanced when it does not rotate.

Condition for balance:

Total clockwise moments=Total anticlockwise moment

Since both are equal → the ruler is balanced

Important:

• If clockwise > anticlockwise → object turns clockwise

• If anticlockwise > clockwise → object turns anticlockwise

3. Moment of a Force

The moment of a force tells us how strongly a force can rotate an object.

Formula:

Moment=Force × Perpendicular distance

Units:

• Force → newtons (N)

• Distance → meters (m)

• Moment → newton-meters (Nm)

Example:

A door:

• Pivot = hinges

• Force = push on the door

Pushing near the hinge → small moment Pushing far from the hinge → large moment

That’s why door handles are far from hinges.

4. Using Moments

The principle of moments is used in many real-life situations:

Everyday examples:

1. Seesaws – children balance by changing position

2. Door handles – placed far from hinges

3. Spanners/Wrenches – longer handle gives more turning effect

4. Balance scales – used to measure mass

5. Cranes – prevent toppling by balancing loads

6. Human body – muscles create moments around joints

In problems:

Moments are used to:

• Find unknown forces

• Find unknown distances

• Check if an object is balanced