CBSE Class 8 Science Chapter 12 Friction NCERT Solutions

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NCERT Solutions PDF Class 8 PDF

This chapter delves into the fundamental concept of friction, a force that opposes motion between surfaces in contact. The NCERT Solutions for Class 8 Science, Chapter 12, provide clear explanations and step-by-step solutions to exercises covering various aspects of friction. Students will learn about the factors influencing friction, such as the nature of surfaces and the force pressing them together. The solutions also explore different types of friction, including static, sliding, and rolling friction, and their relative magnitudes. Additionally, the importance of friction in everyday life, from walking to using brakes, and methods to increase or decrease friction are discussed. These solutions are designed to help students grasp the core principles of friction and prepare effectively for their examinations by offering detailed problem-solving approaches.

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Quick info

BoardCBSE
ClassClass 8
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 12: Friction

Chapter summary

Chapter 12 on Friction in Class 8 Science NCERT Solutions explains the force that opposes motion between surfaces. It covers the definition of friction, factors affecting it like roughness, and the heat it generates. The solutions detail the differences between static, sliding, and rolling friction, and their order of magnitude. It also touches upon increasing and decreasing friction, and its practical applications, providing students with a solid understanding of this essential physical concept.

Learning outcomes

  • Understand that friction is a force opposing motion between surfaces.
  • Identify factors that affect the magnitude of friction.
  • Differentiate between static, sliding, and rolling friction.
  • Explain the role of friction in everyday activities.
  • Describe methods to increase or decrease friction.
  • Solve problems related to friction in various scenarios.

Topics covered

Paper topics

  • Friction
  • Force
  • Motion
  • Roughness of surfaces
  • Heat produced by friction
  • Static friction
  • Sliding friction
  • Rolling friction
  • Increasing friction
  • Decreasing friction
  • Lubricants
  • Applications of friction

Important topics

  • Definition and nature of friction
  • Comparison of static, sliding, and rolling friction
  • Factors affecting friction
  • Methods to increase and decrease friction
  • Real-world applications of friction

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Questions and Solutions

Question 1

Fill in the blanks: (a) Friction opposes the _____ between the surfaces in contact with each other. (b) Friction depends on the ______ of surfaces. (c) Friction produces _____. (d) Sprinkling of powder on the carrom board _____ friction. (e) Sliding friction is _____ than the static friction.
Solution: (a) Friction opposes the motion between the surfaces in contact with each other. This is because friction acts in the direction opposite to the applied force or the direction of motion. (b) Friction depends on the roughness of surfaces. The rougher the surfaces, the greater the friction between them. (c) Friction produces heat. When surfaces rub against each other, the kinetic energy is converted into heat energy due to the resistance. (d) Sprinkling of powder on the carrom board reduces friction. The powder acts as a lubricant, minimizing the contact between the board and the striker/coins, thus decreasing resistance. (e) Sliding friction is lesser than the static friction. It requires more force to start an object moving (overcoming static friction) than to keep it moving (overcoming sliding friction).

Question 2

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement. (a) Rolling, static, sliding (b) Rolling, sliding, static (c) Static, sliding, rolling (d) Sliding, static, rolling
Solution: The correct arrangement is (c) Static, sliding, rolling. This is because static friction is the force that must be overcome to start an object moving from rest. Once the object is moving, the friction acting on it is sliding friction, which is generally less than static friction. Rolling friction, which occurs when an object rolls over a surface, is typically the smallest of the three types of friction.

Question 3

Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be: (a) Wet marble floor, dry marble floor, newspaper and towel. (b) Newspaper, towel, dry marble floor, wet marble floor. (c) Towel, newspaper, dry marble floor, wet marble floor. (d) Wet marble floor, dry marble floor, towel, newspaper
Solution: The correct order of increasing friction is (d) Wet marble floor, dry marble floor, towel, newspaper. Friction is generally higher on rougher surfaces. A wet marble floor is the smoothest and offers the least friction. A dry marble floor is rougher than a wet one, so it has more friction. A towel and newspaper are rougher surfaces than marble, offering even more friction. Between a towel and newspaper, the newspaper surface is typically rougher, leading to higher friction.

Question 4

Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.
Solution: When a book kept on a tilted writing desk starts sliding down, the frictional force acts in the direction opposite to the motion of the book. Since the book is sliding downwards along the tilt, the frictional force will act upwards along the surface of the desk, opposing this downward motion.

Direction of Frictional Force: Upwards, along the surface of the tilted desk.

Direction of Motion: Downwards, along the surface of the tilted desk.

Diagram showing frictional force opposing motion on a tilted surface.

Question 5

You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?
Solution: It would be more difficult for you to walk on the floor after spilling soapy water on it.

Reason: Soapy water acts as a lubricant. It fills the tiny irregularities present on the surfaces of both the floor and your shoes. This filling reduces the interlocking between the surfaces, significantly decreasing the force of friction. Since friction provides the necessary grip to walk, a reduction in friction makes it harder to gain traction, increasing the chances of slipping and falling.

Question 6

Explain why sportsmen use shoes with spikes.
Solution: Sportsmen use shoes with spikes primarily to increase friction and gain a better grip on the playing surface.

Explanation: The spikes on the shoes dig into the ground (like grass or soil). This increased contact and penetration create a stronger frictional force between the shoes and the ground. A higher frictional force prevents the sportsman from slipping, especially during activities that involve sudden starts, stops, or changes in direction, such as running, jumping, or kicking. This improved grip allows them to perform with more confidence and agility.

Image of sports shoes with spikes.

Common mistakes

  • Confusing the order of static, sliding, and rolling friction.
  • Incorrectly identifying the direction of the frictional force.
  • Not understanding how surface properties affect friction.
  • Misinterpreting the effect of lubricants or powders on friction.

Revision tips

  • Focus on the definitions and differences between static, sliding, and rolling friction.
  • Pay close attention to the direction of friction relative to motion.
  • Understand how surface roughness and lubricants impact friction.
  • Relate the concepts of friction to real-life examples provided in the solutions.

Practice MCQs

Q1. Which type of friction is generally the greatest?

Q2. Friction is a force that:

Q3. Sprinkling powder on a carrom board primarily aims to:

Q4. Why do sportsmen wear shoes with spikes?

Q5. Which of the following arrangements correctly shows friction in decreasing order?

Frequently asked questions

What is friction?

Friction is a force that opposes the relative motion or tendency of motion between surfaces in contact with each other.

What are the different types of friction discussed in Class 8 Science Chapter 12?

The chapter discusses static friction (friction when objects are at rest), sliding friction (friction when objects are sliding over each other), and rolling friction (friction when one object rolls over another).

How does the roughness of surfaces affect friction?

Friction depends on the roughness of the surfaces in contact. Rougher surfaces generally result in greater friction compared to smoother surfaces.

Why is it harder to push a heavy box than a light box?

It is harder to push a heavy box because the force of friction is greater when the weight (and thus the normal force) pressing the surfaces together is greater.

How can friction be reduced?

Friction can be reduced by making the surfaces smoother, using lubricants like oil or grease, or by using ball bearings or rollers.

Why do we need friction?

Friction is essential for many activities, such as walking, gripping objects, and the functioning of brakes in vehicles. Without sufficient friction, we would slip and fall, and vehicles would not be able to stop.

Important links

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