Friction Class 8 Notes | Complete Explanation, MCQs, HOTS, NCERT Questions and Answers
Table of Contents
- Introduction to Friction (घर्षण का परिचय)
- What is Friction?
- Causes of Friction
- Types of Friction
- Advantages of Friction
- Disadvantages of Friction
- Methods to Reduce Friction
- Methods to Increase Friction
- Fluid Friction
- Key Points
- Important Abbreviations
- MCQs with Answers
- HOTS Questions
- Short and Long Answer Questions
- Word Problems
- NCERT Questions and Answers
- Frequently Asked Questions (FAQs)
- Conclusion
Friction Class 8 Notes
Introduction (परिचय)
In our daily life, we walk, write, ride bicycles, and hold objects easily. However, all these activities are possible because of friction. Friction is a force that opposes motion between two surfaces in contact. ( Friction Class 8 ) Previous topic : Cell and structure
दैनिक जीवन में हम चलते हैं, लिखते हैं, साइकिल चलाते हैं और वस्तुओं को पकड़ते हैं। ये सभी कार्य घर्षण के कारण संभव होते हैं। घर्षण एक बल है जो दो संपर्क में आई सतहों के बीच गति का विरोध करता है।
What is Friction? (घर्षण क्या है?)
Definition:
Friction is the force that opposes the motion of one surface over another.
Hindi Definition:
जब दो सतहें एक-दूसरे के संपर्क में होती हैं और एक सतह दूसरी के ऊपर चलने का प्रयास करती है, तब जो विरोधी बल उत्पन्न होता है उसे घर्षण कहते हैं।
Examples
- Walking on the road
- Writing with a pencil
- Applying brakes in vehicles
- Climbing a hill
दैनिक जीवन के उदाहरण
- सड़क पर चलना
- पेंसिल से लिखना
- वाहन में ब्रेक लगाना
- पहाड़ पर चढ़ना
Causes of Friction (घर्षण के कारण)
Friction occurs because surfaces are not perfectly smooth. Even polished surfaces contain tiny irregularities.
Moreover, these irregularities interlock with each other and create resistance to motion.
मुख्य कारण
- Surface roughness
- Interlocking of irregularities
- Contact force between surfaces
Types of Friction (घर्षण के प्रकार) ( Friction Class 8 )
1. Static Friction (स्थैतिक घर्षण)
Static friction acts when an object is at rest.
Example
Pushing a heavy cupboard that does not move immediately.
2. Sliding Friction (सर्पी घर्षण)
Sliding friction acts when one surface slides over another.
Example
Sliding a book on a table.
3. Rolling Friction (लुढ़कन घर्षण)
Rolling friction occurs when an object rolls on a surface.
Example
A wheel moving on a road.
Important Fact
Rolling friction is less than sliding friction.
4. Fluid Friction (द्रव घर्षण)
Fluid friction acts when an object moves through liquids or gases.
Example
- Air resistance on a moving car
- Water resistance on a boat
Advantages of Friction (घर्षण के लाभ)
Friction is very useful in our daily life.
Advantages
- We can walk without slipping.
- Vehicles can move safely.
- Brakes work because of friction.
- We can write on paper.
- Nails stay fixed in walls.
- We can hold objects firmly.
हिंदी में लाभ
- बिना फिसले चल सकते हैं।
- वाहन नियंत्रित रहते हैं।
- ब्रेक कार्य करते हैं।
- लिखना संभव होता है।
- वस्तुओं को पकड़ सकते हैं।
Disadvantages of Friction (घर्षण के हानि)
Although friction is useful, it also has some disadvantages.
Disadvantages
- Produces heat..
- Causes wear and tear.
- Reduces efficiency of machines.
- Wastes energy.
- Increases fuel consumption.
Methods to Reduce Friction (घर्षण कम करने के उपाय)
1. Lubrication
Oil and grease reduce friction.
2. Polishing
Smooth surfaces create less friction.
3. Ball Bearings
Ball bearings convert sliding friction into rolling friction.
4. Streamlined Shapes
Aeroplanes and cars are designed to reduce air resistance.
Methods to Increase Friction (घर्षण बढ़ाने के उपाय)
Examples
- Grooves in shoe soles
- Treads on vehicle tyres
- Sand on slippery roads
- Rough surfaces
Fluid Friction (द्रव घर्षण) ( Friction Class 8 )
The friction exerted by fluids such as water and air is called fluid friction.
Furthermore, fluid friction depends on:
- Speed of the object
- Shape of the object
- Nature of the fluid
Streamlined Shape
A streamlined shape helps reduce fluid friction.
Examples:
- Aeroplanes
- Birds
- Fish
- Racing cars
Key Points (महत्वपूर्ण बिंदु) ( Friction Class 8 )
- Friction is a contact force.
- It opposes motion.
- Rough surfaces produce more friction.
- Smooth surfaces produce less friction.
- Rolling friction is less than sliding friction.
- Lubricants reduce friction.
- Fluid friction is also called drag.
- Friction generates heat.
- Brakes work due to friction.
- Streamlined bodies reduce fluid friction.
Important Abbreviations ( Friction Class 8 )
| Abbreviation | Full Form |
|---|---|
| SI | System International |
| cm | Centimetre |
| mm | Millimetre |
| m | Metre |
| km | Kilometre |
| kg | Kilogram |
| N | Newton |
| km/h | Kilometre per Hour |
Multiple Choice Questions (MCQs)
1. Friction is a
A) Push
B) Pull
C) Force
D) Energy
Answer: C
2. Which friction is the least?
A) Static
B) Sliding
C) Rolling
D) Fluid
Answer: C
3. Oil is used to
A) Increase friction
B) Reduce friction
C) Stop motion
D) Increase weight
Answer: B
4. Friction produces
A) Light
B) Sound
C) Heat
D) Water
Answer: C
5. Tyres have grooves to
A) Increase friction
B) Decrease friction
C) Reduce weight
D) Increase speed
Answer: A
6. Air resistance is an example of
A) Static friction
B) Rolling friction
C) Fluid friction
D) Sliding friction
Answer: C
7. Which is smoother?
A) Sandpaper
B) Glass
C) Stone
D) Road
Answer: B
8. Ball bearings help to
A) Increase friction
B) Reduce friction
C) Increase mass
D) Increase force
Answer: B
9. Friction acts
A) Along motion
B) Opposite to motion
C) Upward
D) Downward
Answer: B
10. Writing is possible because of
A) Gravity
B) Friction
C) Magnetism
D) Electricity
Answer: B
HOTS Questions
1.
Why do racing cars have streamlined bodies?
Answer:
They have streamlined bodies to reduce air friction and increase speed.
2.
Why is it difficult to walk on an icy road?
Answer:
Ice provides very little friction, so feet slip easily.
3.
Why are ball bearings used in machines?
Answer:
They reduce friction and improve efficiency.
4.
Why do tyres wear out after long use?
Answer:
Continuous friction between tyres and roads causes wear and tear.
5.
Why do astronauts find movement difficult in space stations?
Answer:
There is very little friction, making movement difficult.
Short Answer Questions
Q1. What is friction?
Answer:
Friction is the force that opposes motion between two surfaces in contact.
Q2. Name any two types of friction.
Answer:
Static friction and sliding friction.
Q3. What is lubrication?
Answer:
The use of oil or grease to reduce friction is called lubrication.
Q4. What is rolling friction?
Answer:
The friction produced when an object rolls over a surface is called rolling friction.
Q5. What is fluid friction?
Answer:
The friction exerted by air or water on moving objects is called fluid friction.
Long Answer Questions
Q1. Explain advantages and disadvantages of friction.
Answer:
Friction helps us walk, write, hold objects, and stop vehicles. However, it also produces heat, wastes energy, and causes wear and tear of machine parts.
Q2. How can friction be reduced?
Answer:
Friction can be reduced by polishing surfaces, using lubricants, employing ball bearings, and designing streamlined shapes.
Word Problems
Problem 1
A bicycle moves smoothly after oiling its chain. Why?
Answer:
Oil reduces friction between chain links, making movement smoother.
Problem 2
A child slips on a wet floor. Explain.
Answer:
Water reduces friction between the floor and shoes, causing slipping.
Problem 3
Why are spikes provided in athletes’ shoes?
Answer:
Spikes increase friction and provide better grip on the ground.
NCERT Questions and Answers
Q1. Fill in the blanks.
- Friction opposes the ________ between surfaces.
Answer: Motion
- Friction depends on the ________ of surfaces.
Answer: Nature
- Rolling friction is ________ than sliding friction.
Answer: Less
Q2. Explain why objects moving in fluids experience friction.
Answer:
Objects moving through fluids such as air and water experience resistance. This resistance is called fluid friction or drag.
Q3. Why are lubricants used in machines?
Answer:
Lubricants reduce friction, prevent wear and tear, and improve machine efficiency.
Frequently Asked Questions (FAQs)
1. What is friction in simple words?
Friction is a force that resists motion between two touching surfaces.
2. Why is friction important?
Friction helps us walk, write, drive vehicles, and hold objects.
3. Can friction be completely removed?
No, friction cannot be completely removed, but it can be reduced.
4. Which friction is the smallest?
Rolling friction is generally the smallest among common types of friction.
5. What is drag?
Drag is another name for fluid friction.
6. Why are tyres rough?
Tyres are rough to increase friction and prevent slipping.
7. Why do machine parts become hot?
Machine parts become hot because friction generates heat.
Conclusion
Friction is an important force that affects almost every activity in daily life. On one hand, it helps us walk, write, and control vehicles. On the other hand, it causes heat, wear and tear, and energy loss. Therefore, understanding friction is essential for Class 8 Science examinations. Moreover, students should practice MCQs, HOTS, NCERT questions, and numerical problems regularly to score excellent marks in school and competitive exams.
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