Important Questions Class 8 Science Chapter 12

Important Questions Class 8 Science Chapter 12 – Friction

Science is a fascinating subject, but at the same time, it has some concepts which are difficult to comprehend. Thus, students will have to make extra efforts to understand the concepts of Physics, Chemistry and Biology. Chapter 12 of Class 8 Science is about Friction. The chapter covers topics of friction and various factors affecting it. 

Below are the key concepts covered in this chapter:

• Force of Friction
• Factors affecting Friction: Spring Balance
• Friction: A Necessary Evil
• Increasing and Reducing Friction
• Wheels Reduce Friction: Rolling friction, Sliding friction, Static friction
• Fluid Friction 

Extramarks has been providing great online study resources for students from grade 1 – 12. Along with NCERT solutions and chapter-specific study notes, we have created Important Questions Class 8 Science Chapter 12 booklet that will help students to revise all the topics from the chapter while solving these questions. The questions are taken by our Science subject experts from various sources including NCERT textbooks, NCERT Exemplar books, past years’ question papers, CBSE sample papers, etc. 

At Extramarks, we highlight crucial concepts and questions from each chapter which help students with their studies right before their examinations. By solving the Important Questions Class 8 Science Chapter 12, the students will be more familiar with the questions asked in the final exams and develop confidence in answering the questions correctly. Science is a subject which requires deep conceptual understanding, so cramming the answers will not fulfil the purpose, especially in the higher classes. 

So, while solving important questions, students must understand every concept to answer any question easily. This encourages the students to master the topic and increases their confidence in achieving high grades.   

Students should also try to understand the answer writing skill. For example, they can practise diagrams while answering the questions. Students may register themselves now on the Extramarks website and access our complete set of Important Questions Class 8 Science Chapter 12. 

To speed up their learning and improve their academic performance, students can also refer to other study material on our Extramarks websites, including NCERT solutions, NCERT books, CBSE revision notes, past years’ question papers, etc. to begin their preparation without any further delay. 

Get Access to CBSE Class 8 Science Important Questions 2022-23 with Chapter-Wise Solutions

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Important Questions Class 8 Science Chapter 12 – With Solutions

Following are some of the questions and their solutions from our Important Questions Class 8 Science Chapter 12.

Question 1. Write some examples where sliding friction is replaced by rolling friction.

Answer 1. Sliding friction is usually replaced with rolling friction in circular objects since it helps body movement.  Some examples are given below: 

1. In car tyres- Rolling friction helps the car’s movement, and static friction is only used when we apply breaks.
2. Use of ball bearings in bicycles.

Question 2. How can we minimise fluid friction?

Answer 2. Fluid friction can be reduced by allowing bodies to move in suitable fluid shapes, known as streamlining.

Question 3. Why is it difficult to move on a wet surface?

Answer 3. Walking on a wet surface is difficult because the water layer makes the surface smooth. The water coating decreases the friction, making it difficult for the foot to maintain a firm grasp on the floor, causing it to slip.

Question 4. What happens if we push a book gently on the table? Why?

Answer 4. When we push a book gently, it moves for a distance and then suddenly stops due to the friction caused by the surface of the table and the book. 

Question 5. Write a short note on a spring balance.

Answer 5. Spring balance is a device that is used to measure the force applied to a particular object. It is made by a coiled spring that expands when pressure is applied to it.

A pointer on the graded scale moves to gauge the spring’s expansion. The reading on the scale determines the magnitude of the force. The scale has a unit of Newton metre.

Question 6. Suppose you spill a bucket of soapy water on a marble floor by mistake. Would it make it easier or harder to walk on the floor? Why?

Answer 6. It is possible to walk on the floor because of the friction between our feet and the ground. For walking, we push the ground backwards with our feet. The frictional force pushes it in the forward direction and helps us to walk. The friction force decreases between the ground and the feet when soapy water spills on the floor. Hence, it becomes hard to walk on the soapy floor.

Question 7. Explain why sportsmen use shoes with spikes.

Answer 7. Sportsmen use shoes with spikes because of the better grip given by spikes while running. This is because the force of friction between the shoes and the ground increases with the help of spikes.

Question 8. Why bodies moving in fluids must have unique shapes.

Answer 8. When a body moves in a fluid, it feels an opposing force which tries to oppose its motion through the fluid. This opposing force is known as the drag force. This frictional force depends on the body’s shape. The force of friction acting on the objects can be minimised by giving the things a special shape. Hence, it becomes easier for a body to move through the fluid.

Question 9. Whenever the surfaces in contact tend to move or move with respect to each other, the force of friction comes into play-

(a) if the objects are solid.

(b) if one object is liquid.

(c) if one object is gaseous.

(d) irrespective of whether the objects are solid, liquid or gas.

Answer 9 The answer is an option (d) irrespective of whether the objects are solid, liquid or gas.

Explanation:

Force of friction acts on solids, liquids and gases and opposes each other’s motion.

Question 10. A large commercial complex has four ways to reach the main road. One of the paths has loose soil, the second is laid with polished marble, the third is laid with bricks, and the fourth has a gravel surface. It is raining heavily, and Paheli wishes to reach the main road. The path on which she is least likely to slip is

(a) loose soil.

(b) polished marble.

(c) bricks.

(d) gravel.

Answer 10. The answer is option (d) gravel.

Explanation:

The only path that will have a sufficient frictional force to walk easily, hence the answer, is (d) gravel.

Question 11. A marble is allowed to roll down an inclined plane from a fixed height. At the foot of the inclined plane, it moves on a horizontal surface.

 (a) covered with silk cloth

 (b) covered with a layer of sand and

 (c) covered with a glass sheet. On which surface will the marble move the shortest distance?

 Give the reason for your answer.

Answer 11. The answer is an option (b) covered with a layer of sand 

A marble moves up to the shortest distance on the surface covered with sand as it gives maximum friction against its motion.

Question 12. Father and son pushed their car to bring it to the side of the road as it had stalled in the middle of the road. They felt that although they initially had to push with all their might to move the car, the push required to keep the car rolling was smaller once it started rolling. Explain.

Answer 12. This is because initially, they had to apply force to set the card in motion, but once the car started rolling, they had to use force only to balance the rolling friction of the car, the applied force is significantly less.

Question 13. We have two identical metal sheets. One of them is rubbed with sandpaper and the other with ordinary paper. The one sanded with sandpaper shines more than the other. Give a reason.

Answer 13. The friction between the plane paper and the metal sheet is less than between the sandpaper and the metal. This friction acts over the top layer of the metal sheet, which will remove the top layer to make the metal shine.

Question 14. Why, during travelling on a rickshaw, might you have experienced that if the seat cover is very smooth, you tend to slip when brakes are applied suddenly? 

Answer 14. If the seat cover is very smooth, the friction between the seat and our body is significantly less. Because of this reason, we tend to slip when brakes are applied in a rickshaw.

Question 15. What are the factors affecting friction?

Answer 15. Friction depends partially on the smoothness of the contacting surfaces;  if two surfaces are rough, greater force is needed to move them past one another than if they are smooth. However, friction decreases with smoothness only to some extent; friction increases between two extremely smooth surfaces because of increased attractive electrostatic forces between their molecules. Friction does not depend on the surface area in contact between the moving bodies or on the relative speed of the bodies. However, it depends on the magnitude of the forces holding the bodies together.

Question 16. Why is sliding friction slightly smaller than static friction?

Answer 16. Sliding friction is smaller than static friction because two sliding objects find less time to get interlocked against each other’s irregularities of surfaces; as a result, they experience less friction.

Question 17. What would have happened if there had been no friction between chalk and board?

Answer 17. If there was no friction between chalk and board, it would be impossible to write on the board without the friction because there would be no chalk deposits on the board.

Question 18. What is the function of lubricants?

Answer 18. A lubricant is a substance that reduces friction between moving surfaces. It performs the following functions:

1. i) Reduce friction
2. ii) Transfer heat

iii) Carry away contaminants & debris

1. iv) Transmit power
2. v) Protect against wear
3. vi) Prevent corrosion

vii) Seal for gases

viii) Stop the risk of smoke and fire.

Question 19. Why can friction never be eliminated?

Answer 19. Friction can never be eliminated because no surface is perfectly smooth; there are always some irregularities.

Question 20. What is rolling friction?

Answer 20. Rolling friction is a force that resists the rolling of a wheel or other circular object along a surface caused by deformations in the object or surface. Generally, the rolling friction is smaller than the sliding friction. Example: The road movement is one of the most common examples of rolling resistance.

Question 21. Differentiate between sliding and rolling friction.

Answer 21. Friction is called sliding friction when two objects move relative to each other and rub together (like a sledge on the ground). Still, Rolling friction is the force that resists the rolling of a wheel or other circular object along a surface caused by deformations in the object and or surface.

Question 22. Why must objects moving in fluid have special shapes?

Answer 22. The fluids, like various liquids or air, i.e. gaseous medium, also exert frictional force known as  drag. To minimise the effect of this drag, streamlining the movement of the object in the fluid is necessary, which can be achieved by changing the shape of the body. Objects moving in fluids must have a specific shape called streamlined shapes or aerodynamic shapes. A streamlined Shape or Aerodynamic Shape is a shape that overcomes fluid friction. 

Question 23. Why is it hard to walk on a floor wet with soapy water?

Answer 23. It is hard to walk on a floor wet with soapy water because a layer of soap makes the floor smooth and slippery. The layer of soapy water reduces the friction, and the foot cannot grip the floor properly, and it starts to slip on the floor.

Question 24. Explain the function of the spring balance.

Answer 24. Spring balance is made up of a coiled spring that gets stretched when a force is applied. The stretching of the spring is measured by a pointer moving on a graduated scale; the reading on the scale provides us with the magnitude of the force.

Question 25. Explain the advantages and disadvantages of friction.

Answer 25. Advantages of friction-

(i) We cannot write anything with a pen or pencil if there is no friction.

(ii) We can’t write on the blackboard with chalk if there is no friction.

(iii) If an object started moving, it would never stop if there was no friction.

(iv) We cannot walk on a road without friction.

(v) We cannot fix a nail on the wall or tie a knot without friction.

Disadvantages of friction-

(i) It wears out the materials, no matter if they are screws, ball bearings or soles of shoes.

(ii) It produces heat which damages the moving parts of a machine..

(iii) Friction also produces heat when a machine is operated. causing waste of energy in machines.

(iv) The tyres of cars, buses and trucks, etc., also wear out due to friction.

(v) Friction reduces the speed, which requires more force.

In this way, we see that friction can be both destructive and advantageous, so it is a necessary evil.

Benefits of Solving Important Questions Class 8 Science Chapter 12:

Students can face difficulty understanding the new concepts in Science. One way to tackle this is to practise important questions in the chapter. Chapter 12 class 8 Science important questions cover all the essential topics, and these questions are created from an exam perspective and are most likely to be picked by CBSE  in the exam. Solving science class 8 chapter 12 important questions gives students a competitive edge. 

Extramarks leaves no stone unturned to give the best learning material to students while combining fun and learning activities through its own study materials to enhance their learning experience. Here are the benefits of studying important questions in class 8 Science chapter 12: 

• Students will revise everything and cover the entire syllabus, and these questions are created by the subject experts exclusively for the entrance exams. There is a higher chance that some of these questions might be asked in the exam. It gives students an overall idea of how the questions might appear in their exams and helps them to be prepared and confident. 
• All the solutions are checked and verified by subject matter experts in our team. The solutions are prepared in a step-by-step easy to understand language for students to easily comprehend the answers. It brings clarity to concepts which in turn becomes useful when it comes to answering tricky questions. 
• The list of important questions in Class 8 Science Chapter 12 consists of objective types, short answers, and long answers. It has questions ranging from easier to difficult levels for students to practice and gain confidence in the preparation.Students need not refer to other books as Extramarks has all the solutions to their problems as it would be a total wastage of time and may lead to unnecessary stress and anxiety.

We recommend students take guided practice and help to be aware of their mistakes and maximise their potential by learning how to frame the right answer and develop the confidence to achieve excellent scores.

Extramarks believes in incorporating happy and joyful learning experiences through its own repository of resources.Extramarks is a leading online learning platform that offers comprehensive learning solutions to students in classes 1-12. We also offer additional study and course materials. To access the most important resources, students can also click the links below:

• NCERT books
• CBSE Revision Notes
• CBSE syllabus
• CBSE sample papers
• CBSE past years’ question papers
• Important formulas 
• CBSE extra questions