Science · Class 8
Friction
Friction advantages, disadvantages, and methods to increase or reduce it.
4 sections15–25 min read6 MCQs · 2 examples
Chapter Overview
Friction opposes relative motion between surfaces in contact. This chapter covers types of friction, factors affecting it, advantages/disadvantages, and methods to increase or reduce friction.
Types of Friction
- Static: before motion starts
- Sliding: object moves over surface
- Rolling: wheel on road — least among these
- Fluid friction (drag) in liquids and gases
Factors and Control
- Depends on nature of surfaces and how hard they press
- Increase: treads on tyres, grooves on soles
- Reduce: lubricants, ball bearings, polishing
- Streamlined shape reduces air/water resistance
Applications
- Walking possible due to friction
- Without friction, brakes fail
- Heat from friction — matchstick lighting
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Friction types
Which friction is less: sliding or rolling?
- 1Rolling friction much less
- 2Wheels reduce sliding friction
- 3Ball bearings convert sliding to rolling
Answer
Rolling friction is less
Reduce friction
How do lubricants help machines?
- 1Form thin layer between surfaces
- 2Prevent direct metal contact
- 3Reduce heat and wear
Answer
Separate surfaces to reduce friction
Key Points to Remember
- ✓ Friction produces heat — useful and harmful
- ✓ Static electricity sometimes from friction
- ✓ Drag increases with speed
Exam Tips
- • Give examples where friction is useful and harmful
- • Why are tyres treaded?
- • Distinguish static, sliding, rolling friction
Practice MCQs — Friction
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 6Score: 0/0
Friction acts: