CBSE Class 8 Science Exemplar Chapter 12: Friction NCERT Solutions

Reviewed by · Updated on

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 Exemplar Chapter 12 provide clear explanations and step-by-step solutions to various questions. Students will explore how friction acts on solids, liquids, and gases, and understand its direction relative to motion. The solutions also cover practical applications, such as how lubricants like oil reduce friction and how different surfaces affect the distance traveled by an object. By working through these problems, students will gain a deeper understanding of the principles of friction and its impact on everyday phenomena, aiding in their exam preparation and scientific comprehension.

Home

Quick info

BoardCBSE
ClassClass 8
SubjectScience Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 12

Chapter summary

Chapter 12 of the CBSE Class 8 Science Exemplar focuses on Friction. The NCERT Solutions cover multiple-choice questions and other problems that explain the nature of friction, its direction of action, and its dependence on the state of matter (solid, liquid, gas). It also touches upon practical aspects like using lubricants to reduce friction and how surface properties influence the extent of friction, helping students grasp the core concepts through solved examples.

Learning outcomes

  • Understand that friction acts between surfaces in contact, opposing relative motion.
  • Identify the direction of the force of friction relative to the direction of motion.
  • Recognize that friction applies to solids, liquids, and gases.
  • Explain the role of lubricants in reducing friction.
  • Compare the effect of different surfaces on the magnitude of friction.

Topics covered

Paper topics

  • Friction
  • Force of Friction
  • Direction of Friction
  • Friction in Solids
  • Friction in Liquids
  • Friction in Gases
  • Lubricants
  • Effect of Surface on Friction
  • Sharpening Blades
  • Reducing Friction

Important topics

  • Nature and Direction of Friction
  • Friction in Different States of Matter
  • Role of Lubricants
  • Impact of Surface Roughness on Friction

PDF preview

Read page by page below. PDF is streamed from the official NCERT website — no download button on this page.

Loading document …
Page of
Loading page …

Questions and Solutions

Multiple Choice Questions

Question 1

Whenever the surfaces in contact tend to move or move with respect to each other, the force of friction:
Solution: The correct answer is (d) irrespective of whether the objects are solid, liquid or gaseous. Friction is a force that opposes relative motion between any two surfaces in contact. This opposition to motion occurs whether the surfaces are solid, liquid, or gaseous. Therefore, friction is not limited to solids and applies across different states of matter.

Question 2

In Fig.12.1, a boy is shown pushing the box from right to left. The force of friction will act on the box:
Solution: The correct answer is (b) from left to right (→ ). The force of friction always acts in the direction opposite to the direction of motion or the tendency of motion. Since the boy is pushing the box from right to left, the box is either moving or tending to move in that direction. Consequently, the force of friction will oppose this motion by acting from left to right.

Question 3

To sharpen the blade of a knife by rubbing it against a surface, which of the following will be most suitable? (a) stone (b) plastic block (c) wooden block (d) glass block
Solution: The most suitable option is (a) stone. Sharpening a blade involves removing small amounts of material from the edge to make it finer. This is achieved through friction. A rougher surface, like that of a stone, exerts a greater frictional force compared to smoother surfaces like plastic, wood, or glass. This higher friction effectively grinds down the blade's edge, making it sharper.

Question 4

A toy car released with the same initial speed will travel farthest on: (a) muddy surface (b) polished marble surface (c) cemented surface (d) brick surface
Solution: The correct answer is (b) polished marble surface. The distance a toy car travels depends on the friction it encounters. A muddy, cemented, or brick surface is generally rougher and will exert a greater frictional force, slowing the car down more quickly. A polished marble surface is much smoother and offers significantly less resistance (lower friction), allowing the car to maintain its motion for a longer distance before coming to a stop.

Question 5

If we apply oil on door hinges, the friction will: (a) increase (b) decrease (c) disappear altogether (d) will remain unchanged
Solution: The correct answer is (b) decrease. Oil acts as a lubricant when applied to surfaces like door hinges. Lubricants work by reducing the friction between the moving parts. They create a thin layer between the surfaces, preventing direct contact and making it easier for them to slide past each other, thus decreasing the overall friction and allowing the hinges to move more smoothly.

Common mistakes

  • Confusing the direction of friction with the direction of applied force.
  • Assuming friction only occurs between solid surfaces.
  • Not understanding that lubricants reduce friction by creating a smoother interface.

Revision tips

  • Review the direction of friction in relation to motion for each question.
  • Pay close attention to the explanations for why certain surfaces cause more or less friction.
  • Understand the practical examples, like oiling hinges, to solidify the concept of lubricants.

Practice MCQs

Q1. When surfaces in contact tend to move or are in motion relative to each other, the force of friction:

Q2. A boy pushes a box from right to left. In which direction will the force of friction act on the box?

Q3. To sharpen a knife's blade by rubbing it against a surface, which material would be most suitable?

Q4. A toy car, released with the same initial speed, will travel the farthest on which type of surface?

Q5. What happens to the friction in door hinges when oil is applied?

Frequently asked questions

What is friction according to CBSE Class 8 Science Exemplar Chapter 12?

Friction is a force that comes into play when the surfaces in contact tend to move or move with respect to each other. It always opposes the motion.

Does friction apply only to solid objects?

No, friction applies irrespective of whether the objects are solid, liquid, or gaseous. It opposes relative motion between surfaces in contact.

In which direction does the force of friction act?

The force of friction always acts in the direction opposite to the direction of motion or the tendency of motion between the surfaces in contact.

How does applying oil to door hinges affect friction?

Applying oil to door hinges reduces friction. Oil acts as a lubricant, making it easier for the hinges to move.

Which type of surface will allow a toy car to travel the farthest?

A polished marble surface will allow a toy car to travel the farthest because it has the least frictional force compared to muddy, cemented, or brick surfaces.

Why is a stone suitable for sharpening a knife blade?

A stone is suitable because its rough surface exerts a greater frictional force, which helps to wear down the blade and make it sharper.

Important links

Content reviewed by the NCERT Help team. Editorial Team and update policy

NCERT Solutions PDF PDF on NCERT Help. URL unchanged for search indexing.