Short Introduction
Turning effect of force is one of the most important concepts in ICSE Class 10 Physics. Whenever a force causes an object to rotate, the turning effect produced is called Moment of Force or Torque.
This chapter includes:
- Moment of Force
- Torque
- Principle of Moments
- Equilibrium
- Centre of Gravity
- Stable and Unstable Equilibrium
- Important Numericals
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Updated Date: 17 May 2026
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1. What is Turning Effect of Force?
Sometimes force not only moves an object but also rotates it. This rotational effect is called Moment of Force or Torque.
Examples
- Opening a door
- Turning steering wheel
- Pedalling bicycle
- Tightening nut with spanner
2. Moment of Force (Torque)
The turning effect produced by a force about a fixed point is called Moment of Force.
| Symbol | Meaning |
|---|---|
| M | Moment of Force |
| F | Force Applied |
| d | Perpendicular Distance |
Units
| System | Unit |
|---|---|
| SI Unit | Newton metre (Nm) |
| CGS Unit | Dyne centimetre |
3. Principle of Moments
For a body in equilibrium:
Example Numerical
A 10 N force acts at 40 cm from pivot. Another force acts at 20 cm. Find the second force.
4. Equilibrium
A body is said to be in equilibrium when it does not move or rotate.
Types of Equilibrium
| Type | Description |
|---|---|
| Translational Equilibrium | Resultant force is zero |
| Rotational Equilibrium | Clockwise moment equals anticlockwise moment |
5. Centre of Gravity
The point through which the entire weight of a body acts is called Centre of Gravity.
| Body | Centre of Gravity |
|---|---|
| Uniform Rod | Middle |
| Ring | Centre |
| Sphere | Centre |
| Rectangle | Intersection of diagonals |
6. Stable, Unstable and Neutral Equilibrium
| Type | Example | Condition |
|---|---|---|
| Stable | Ball in bowl | C.G. rises on disturbance |
| Unstable | Ball on hill top | C.G. lowers on disturbance |
| Neutral | Ball on floor | C.G. remains same |
7. Daily Life Applications
- Door handles are fixed far from hinges.
- Long spanners produce greater torque.
- Steering wheels are large for easier turning.
- Seesaw balancing uses principle of moments.
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What is Moment of Force?
The turning effect produced by a force about a pivot is called Moment of Force.
What is the SI unit of Torque?
Newton metre (Nm).
What is Centre of Gravity?
It is the point through which the entire weight of the body acts.
Why are door handles fixed far from hinges?
Larger distance produces greater moment and makes opening easier.
What is Stable Equilibrium?
A body returns to original position after disturbance.