NCERT Class 8 Science Science: Chapter 9 — Friction
This chapter introduces the concept of friction, a force that opposes motion between surfaces in contact. It explains why moving objects slow down and eventually stop without an external force, using examples like a ball rolling on the ground or a bicycle with applied brakes. Activities demonstrate how friction opposes the applied force, acting in the opposite direction of motion. The chapter also explores factors affecting friction, such as the nature of surfaces, and introduces the spring balance as a device to measure force. It poses questions about why friction differs for various surfaces and how smoothness impacts it, setting the stage for further exploration of friction's properties and effects in Class 8 Science.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 8 |
| Subject | Science |
| Book | Science |
| Chapter | Chapter 9 — Friction |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 3 minutes |
| Word count | 451 |
Learning outcomes
- Define and explain the force of friction.
- Understand that friction opposes the motion of objects.
- Identify situations where friction is present.
- Recognize that friction depends on the nature of surfaces.
- Learn about the spring balance as a tool to measure force.
Vocabulary
| Word | Meaning |
|---|---|
| Friction | A force that opposes motion between surfaces in contact. |
| Applied force | The force that is put on an object to make it move. |
| Opposes | To act against or be in conflict with. |
| Spring balance | A device used for measuring the force acting on an object. |
| Graduated scale | A scale with markings to measure a quantity. |
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Practice questions
- What is the force of friction? Answer: The force of friction is a force that opposes the motion between surfaces in contact.
- Why does a moving ball on the ground stop after some time? Answer: A moving ball stops because of the force of friction acting between the ball and the ground, which opposes its motion.
- In which direction does the force of friction act? Answer: The force of friction acts in the direction opposite to the applied force or the motion of the object.
- What is a spring balance used for? Answer: A spring balance is used for measuring the force acting on an object.
Frequently asked questions
What is the force of friction?
Friction is a force that opposes the relative motion between two surfaces in contact.
Why do vehicles slow down when brakes are applied?
When brakes are applied, they create friction between the brake pads and the wheel, which opposes the motion and slows down the vehicle.
What happens if no external force is applied to a moving object?
If no external force is applied, friction will eventually oppose the motion, causing the object to slow down and stop.
How does friction act relative to the motion of an object?
The force of friction always acts in the direction opposite to the motion of the object.
What is a spring balance?
A spring balance is a device used to measure the magnitude of a force acting on an object.
Does friction depend on the surfaces involved?
Yes, friction depends on the nature of the surfaces in contact; rougher surfaces generally have more friction than smoother ones.
Related resources
Important topics
Topics covered
NCERT Class 8 Science — Science — Chapter 9 — Friction. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.