VERY SHORT ANSWER TYPE QUESTIONS
Q. 1. What is force of friction?
Ans. The force acting on a moving body which is equal and opposite to the direction of motion is called force of friction.
Q. 2. Is the friction the same for all the surfaces?
Ans. No, friction is not the same for all the surfaces.
Q. 3. Does friction depend on the nature of objects?
Ans. Yes, friction depends on nature of objects.
Q. 4. Does friction depend on smoothness of the surface?
Ans. Yes, friction depends on the smoothness of the surface.
Q. 5. Which surface produces more friction?
Ans. Rough surface produces more friction.
Q. 6. Which type of surface produces less friction?
Ans. Smooth surface produces less friction.
Q. 7. What is the direction of frictional force?
Ans. The direction of frictional force is opposite to the motion.
Q. 8. What is the cause of friction between two surfaces?
Ans. Friction is caused by the irregularities on the two surfaces in contact.
Q. 9. Which surface has more irregularities, smooth or rough surface?
Ans. Rough surface has more irregularities.
Q . 10. How many types of friction are there?
Ans. There are three types of friction: (i) Static friction (ii) Sliding friction (iii) Rolling friction
Q . 11. Which is less, sliding friction or static friction?
Ans. Sliding friction is smaller than the static friction.
Q . 12. Which force helps to write by chalk on the blackboard?
Ans. Frictional force.
Q . 13. Which is easier to hold, an earthen pot or a glass tumbler?
Ans. Holding earthen pot is easier than holding a glass tumbler.
Q . 14. Why is it difficult to move on a wet marble floor?
Ans. Wet marble floor has less friction, so it is difficult to move on it.
Q . 15. What does friction do to soles of our shoes?
Ans. Friction causes wear and tear in soles of our shoes.
Q . 16. Why does a matchstick catch fire when it is rubbed on a rough surface?
Ans. Matchstick catches fire due to friction.
Q . 17. What happens when there is no friction between the chalk and the blackboard?
Ans. We cannot write on the blackboard.
Q . 18. What would happen when an object starts moving if there is no friction?
Ans. The object would never stop if there is no friction.
Q . 19. What does friction produce?
Q . 20. Write one harm of friction.
Ans. Friction wears out the materials, like machine parts.
Q . 21. Why does jar of a mixer become hot when it is run for few minutes?
Ans. The jar of a mixer becomes hot due to friction.
Q . 22. Why do the tyres of cars and trucks are treaded?
Ans. The treaded tyres of cars and trucks provide better grip with the ground.
Q . 23. Why do Kabaddi players rub their hands with soil?
Ans. Kabaddi players rub their hands with soil for a better grip of their opponents.
Q . 24. Give two examples where friction is undesirable.
Ans. (i) We sprinkle fine powder on carrom board to reduce friction.
(ii) Drops of oil are poured on the hinges of a door so that the door moves smoothly.
Q . 25. What do you mean by lubricants?
Ans. The substances which are used to reduce friction are called lubricants.
Q . 26. Why are oil, creams and grease called lubricants?
Ans. Oil, creams and grease are called lubricants because they are used to reduce friction.
Q . 27. How are the shoes made to counter the friction and make better grip?
Ans. They have grooves on their soles.
Q. 28. What is used in cycle brakes to increase friction?
Ans. Brake pads.
Q . 29. Name the substance which is used in carrom board to reduce friction.
Ans. Talcum powder.
Q . 30. What is avoided between two surfaces to make movement smooth?
Ans. Interlocking of irregularities is avoided.
Q . 31. Can we eliminate friction completely?
Ans. No, we cannot eliminate friction completely.
Q . 32. What is used to reduce friction in machines where lubrication are not advisable?
Ans. Air cushion.
Q . 33. Why do pieces of luggage fitted with rollers?
Ans. Pieces of luggage are fitted with rollers to reduce single friction so that children can pull such pieces of luggage easily.
Q . 34. Name two methods of reducing friction.
Ans. (i) By rolling
(ii) By sliding.
Q . 35. How sliding friction is replaced by rolling in machines?
Ans. By using ball bearings.
Q . 36. Name any machine in which ball bearing is used to reduce friction.
Ans. Ceiling fan.
Q . 37. What is drag?
Ans. The frictional force exerted by fluids is called drag.
Q . 38. What are fluids?
Ans. Commonly gases and liquids are called fluids.
Q . 39. What does frictional force exerted on an object in a fluid depend on?
Ans. Friction depends on the speed with respect to the fluid and the nature of fluid.
Q . 40. Name the special shape given to objects moving in fluid.
Ans. Streamlined shape.
Q . 41. Name some objects which have streamlined body.
Ans. Boats, aeroplanes and ships.
Q . 42. When does rolling friction come into play?
Ans. When a body rolls on other body then rolling friction comes into play.