Extra 30 short questions and answers from Chapter:9 Friction (Class 8 Science - CBSE):-

1. What is friction?

Friction is the force that opposes the relative motion between two surfaces in contact.

2. What causes friction?

Friction is caused by the roughness of surfaces in contact and the interlocking of their microscopic irregularities.

3. Name the different types of friction.

The types of friction are:

Static friction

Sliding friction

Rolling friction

Fluid friction

4. Which type of friction is the highest and why?

Static friction is the highest because it resists the initial motion of an object and requires more force to overcome.

5. Why is rolling friction less than sliding friction?

Rolling friction is less than sliding friction because in rolling, the area of contact between surfaces is smaller, reducing resistance.

6. How does friction help us in daily life?

Friction helps us in walking, holding objects, lighting a matchstick, writing with a pen, and stopping vehicles.

7. Why do we sprinkle powder on a carrom board?

We sprinkle powder on a carrom board to reduce friction, allowing smooth movement of coins.

8. Why do soles of shoes wear out after prolonged use?

The continuous friction between the shoe soles and the ground causes wear and tear, leading to thinning of the soles.

9. Why is it difficult to walk on a smooth or wet floor?

A smooth or wet floor has less friction, making it difficult to get a grip and causing us to slip.

10. What is fluid friction?

Fluid friction, also called drag, is the resistance experienced by objects moving through fluids (liquids or gases).

11. How can friction be reduced?

Friction can be reduced by using lubricants, polishing surfaces, using ball bearings, or streamlining objects.

12. Why are lubricants used in machines?

Lubricants reduce friction between moving parts, preventing wear and overheating of machines.

13. Why do cars and aeroplanes have streamlined shapes?

A streamlined shape reduces fluid friction, allowing the object to move smoothly through air or water.

14. How does friction produce heat?

When two surfaces rub against each other, their microscopic irregularities generate heat due to friction.

15. Why do tyres have grooves?

Grooves in tyres increase friction, providing better grip and preventing slipping on roads.

16. Why do gymnasts apply powder on their hands?

Gymnasts apply powder to increase friction and get a better grip while performing.

17. What is the role of friction in braking a vehicle?

Friction between the brake pads and the wheels helps stop the vehicle by opposing its motion.

18. Why do birds and fish have streamlined bodies?

A streamlined body reduces fluid friction, helping birds fly and fish swim efficiently.

19. Why do we use ball bearings in machines?

Ball bearings reduce rolling friction and make the movement of machine parts smoother.

20. How does friction help in writing with a pencil?

Friction between the pencil tip and the paper helps transfer graphite onto the paper, making writing possible.

21. Why is it easier to pull a suitcase with wheels than to drag it?

Rolling friction is less than sliding friction, so using wheels reduces the force required to move the suitcase.

22. How does friction help in walking?

Friction between our feet and the ground prevents slipping and allows us to walk.

23. Why do moving objects eventually stop if no force is applied?

Friction opposes motion and gradually slows down the moving object until it stops.

24. Why is it difficult to drag a heavy box on the floor?

A heavy box has more weight, increasing friction between the box and the floor, making it harder to drag.

25. Why do racing cars have smooth tyres?

Smooth tyres reduce friction, allowing the car to move faster with less resistance.

26. How does oiling bicycle chains help in smooth movement?

Oiling reduces friction between the chain and gears, making pedaling easier.

27. How do brakes work in a bicycle?

When the brake pads press against the wheels, friction slows down or stops the bicycle.

28. Why do spaceship surfaces burn when entering the Earth's atmosphere?

High-speed movement through the atmosphere creates extreme friction, generating heat that can burn the surface.

29. What happens if there is no friction?

Without friction, we cannot walk, hold objects, write, stop vehicles, or perform many daily activities.

30. How do streamlined shapes help in reducing fluid friction?

Streamlined shapes allow smooth flow of air or water around objects, reducing drag and increasing efficiency.