NCERT Exemplar for Class 8 Science Solutions Chapter 12 Friction

Multiple Choice Questions

1. Whenever the surfaces in contact tend to move or move with respect to each other,

the force of friction comes into play

(a) only if the objects are solid.

(b) only if one of the two objects is liquid.

(c) only if one of the two objects is gaseous.

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

Ans: (d) irrespective of whether the objects are solid, liquid or gaseous. For friction, the state of matter does not change.

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

(a) from right to left ($ \leftarrow $) 

(b) from left to right ($ \to $) 

(c) vertically downwards ($ \downarrow $)

(d) vertically upwards ($ \uparrow $)

Ans: (b) from left to right (\[ \to \]). The friction will act as an opposite force so it will work in the opposite direction. ($ \to $)

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

Ans: (a) stone. Stone will exert more friction and reaction, which will help to sharpen the blade of the knife.

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

Ans: (b) polished marble surface. The car will travel the greatest distance on the surface with the least amount of resistance. As a result, the marbled surface will be ideal for car movement.

5. If we apply oil on door hinges, the friction will

(a) increase 

(b) decrease

(c) disappear altogether 

(d) will remain unchanged

Ans: (b) decrease. Friction between two surfaces is always decreased by lubrication. As a result, putting oil on the surface will reduce friction.

6. Which of the following statements is incorrect?

(a) Friction acts on a ball rolling along the ground.

(b) Friction acts on a boat moving on water.

(c) Friction acts on a bicycle moving on a smooth road.

(d) Friction does not act on a ball moving through air.

Ans: (d) Friction does not act on a ball moving through air. Friction among air particles acts on a ball moving through air. This is called air resistance.

7. A boy rolls a rubber ball on a wooden surface. The ball travels a short distance before coming to rest. To make the same ball travel longer distance before coming to rest, he may

(a) spread a carpet on the wooden surface.

(b) cover the ball with a piece of cloth.

(c) sprinkle talcum powder on the wooden surface.

(d) sprinkle sand on the wooden surface.

Ans: (c) sprinkle talcum powder on the wooden surface. The power reduces the friction between the surfaces. So, the ball will go at a longer distance due to less friction.

8. In a large commercial complex there are 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.

Ans: (d) Gravel. The gravel surface will be suitable for her walk. Gravel has sufficient friction.

Very Short Answer Questions

9. Two blocks of iron of different masses are kept on a cemented floor as shown in Fig.12.2. Which one of them would require a larger force to move it from the rest position?

Ans: The 2 kg iron block will create more friction. As we all know, friction increases as weight increases. Hence, the 2kg block will require larger force to move it.

10. Will the force of friction come into play when a raindrop rolls down a glass window pane?

Ans: Yes. The frictional force holding the raindrop on the window surface is insufficient due to the smooth surface of the window, and the raindrop rolls down.

11. Two boys are riding their bicycles on the same concrete road. One has new tyres on his bicycle while the other has tyres that are old and used. Which of them is more likely to skid while moving through a patch of the road which has lubricating oil spilled over it?

Ans: The bicycle with old tyres is more likely to skid because it’ll have less grooves which is essential to improve the bicycle’s grip and  to create necessary friction to stop it from slipping.

12. Fig.12.3 shows two boys applying force on a box. If the magnitude of the force applied by each is equal, will the box experience any force of friction?

Ans: The force generated by both boys will cancel each other out, resulting in a force of zero. As a consequence, the friction force will be zero.

13. Imagine that an object is falling through a long straight glass tube held vertical; air has been removed completely from the tube. The object does not touch the walls of the tube. Will the object experience any force of friction?

Ans: No. The falling object will not feel any friction.

C. Short Answer Questions

14. You might have noticed that when used for a long time, slippers with rubber soles become slippery. Explain the reason.

Ans: After a long time of wearing slippers, the sole becomes smooth, reducing the necessary force of friction between the slipper and the floor, causing the slipper to become slippery.

15. Is there a force of friction between the wheels of a moving train and iron rails? If yes, name the type of friction. If an air cushion can be introduced between the wheel and the rail, what effect will it have on the friction?

Ans: Yes, the rolling force between the wheels and the iron nails is effective. The friction between these will decrease if a cushion is introduced between them.

16. Cartilage is present in the joints of our body, which helps in their smooth movement. With advancing age, this cartilage wears off. How would this affect the movement of joints?

Ans: The friction in cartilage will increase, making it hard to move, which will result in joint pain.

17. While playing tug of war (Fig.12.4), Preeti felt that the rope was slipping through her hands. Suggest a way out for her to prevent this.

Ans: To increase the friction, she could rub soil on the rope. 

18. The handle of a cricket bat or a badminton racquet is usually rough. Explain the reason. 

Ans: The roughness of the cricket bat and badminton racquet handle makes it easier to grip due to increased friction. 

19. Explain why the surface of mortar and pestle (silbatta) used for grinding is etched again after prolonged use? 

Ans: Silbatta becomes smooth after a long period of use. Etching becomes necessary to make it more effective since etching increases friction.

20. 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 reason for your answer. 

Ans:  On a sand-covered floor, the marble will move the slowest. Sand will cause additional friction between the marble and the floor, making it difficult to move for longer periods of time.

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

Ans: This is because they had to push the car to put it in motion; once the car started moving, they only had to balance its rolling. Giving motion to a static object demands more friction as compared to balancing it.

22. When the cutting edge of a knife is put against a fast rotating stone to sharpen it, sparks are seen to fly. Explain the reason. 

Ans: Heat is produced when a knife is sharpened by rubbing it on a revolving stone. As the rotational speed of the stone increases, so does the heat on the knife, causing it to spark.

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

Ans: When compared to an ordinary paper, sand paper creates more friction between the metal sheet and it. As a result, the sandpaper removes the top layer of the metal sheet, making it shinier. 

24. While travelling on a rickshaw, you might have experienced that if the seat cover is very smooth, you tend to slip when brakes are applied suddenly. Explain. 

Ans: It's hard to create the necessary friction between the person and the seat when the seat cover is plain and smooth. As a result, the passenger slips forward when the brake is applied.

25. Two friends are trying to push a heavy load as shown in Fig.12.5. Suggest a way which will make this task easier for them.

Ans: They can use rollers to make their work easier. They can easily move the load by placing the rollers beneath it. When compared to a plain heavy load, rollers require less friction.

Introduction Chapter 12- Friction

Class 8 Science NCERT Exemplar Solutions Chapter 12 Friction prepares the students for all the important physical-related topics that are covered in the syllabus of 2024-25. The exemplar solutions guide the students in getting higher knowledge about the topics.

After a deep study and vast research, the Vedantu’s expert teachers have prepared the NCERT Exemplar solutions for Class 8th Science Chapter 12- friction. Also, students can take classes to clear their doubts, and also they can download the solution PDF available on our site to get a  revision.

Class 8th Science Chapter 12 covers the basic questions like friction Class 8 Multiple choice questions, friction quiz with answers, extra questions Class 8 frictions, Worksheets Class 8 friction, important questions on the important topics, numerical questions and other problems, practical questions. In order to score well, you need to work on them regularly and understand the concepts well.

Topics covered under NCERT Exemplar Class 8 Science Chapter 12 Friction

You can get complete knowledge about the topics covered under this chapter and get complete details of the most important topic which you have to throw in order to prepare this chapter for your examination. Here is the list of topics covered under Class 8 Science Chapter 12 Friction:

• Force of Friction

• Factors affecting Friction

• Friction: A Necessary Evil

• Increasing and Reducing Friction

• Wheels Reduce Friction

• Fluid Friction.

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