Friction Worksheet-7

Friction Worksheet-7

61. Our hands become warm when we rub them. Why?

62. Mention three examples which show that friction produces heat.

63. We observe that in some cases we want to increase friction. Explain why.

64. Why do we need to decrease friction and how it can be decreased?

65. How do wheels reduce friction?

66. What are the factors on which frictional force depends in fluids?

67. Why do we shape aeroplanes like that of a bird?

68. Friction is called necessary evil. Why?

69. Write some methods used to reduce friction.

70. Explain various types of frictions.

71. What is fluid friction? Write the factors on which fluid friction depends.

Answer:

61. When we rub our hands with each other or with any surface the friction arises. The friction produces heat, that makes our hands warm.

62. (i) If we rub our hands with each other they become hot because of friction

(ii) Jar of mixer or grinder becomes hot when it is run or operated.

(iii) Warming of the parts of a machine when it is operated.

(iv) The tires of car get hot after long driving because of friction

63. Friction is sometimes boon sometimes enemy. We want friction to be there in some cases for a proper working. For example if there were no friction it would have been difficult for us to walk or run on the road or floor. We or vehicles would slip on road if there is no friction and moreover it would have been difficult to stop them. It is not easy to walk and write without friction. It can be observed that friction is increased by making roads with concrete. Vehicles are stopped by applying brakes.

64. Friction is sometimes boon sometimes enemy. It causes a lot of wear and tear in objects. It also damages the machine parts. So sometimes we need to decrease the friction. It can be done by rolling, sliding and lubricating the surface in contact. We use ball bearing, wheels and lubricants like grease, oils and creams to decrease the friction. That results in smooth functioning of machines.

65. Wheels are used to reduce friction. The wheels reduce the resistance against motion. So it is easy to roll the body over one another than to slide a body.

66. (i) The frictional force on an object in a fluid depends on its speed with respect to the fluid.

(ii) Frictional force also depends on the shape of the object and the nature of the fluid.

67. The objects are given special shapes to minimize or reduce the friction. Aero plane and birds both fly in the air and have to face friction exerted by air. They are so shaped that they do not have to lose much energy to overcome the frictional force exerted by air to fly.

68. Friction is sometimes boon sometimes enemy. We want friction to be there in some cases for a proper working. For example if there were no friction it would have been difficult for us to walk or run on the road or floor. We or vehicles would slip on road if there is no friction and moreover it would have been difficult to stop them. It is not easy to walk and write without friction. It can be observed that friction is increased by making roads with concrete. Vehicles are stopped by applying brakes.

69. (i)  Fine powder is used on carrom board to reduce friction and better playing experience.

(ii) Oils, lubricants, graphite powder and air cushion or grease are used for proper and smooth functioning of machine parts.

(iii) Spikes are used in sports shoes to reduce the friction so the athlete can run fast and do not slip

70. There are following types of frictions:

(i) Static friction (ii) Sliding friction (iii) Rolling friction

(i) Static friction: This friction which is produced between two surfaces in contact with each other at the position of rest. This is most powerful friction. It takes a lot of energy to overcome this friction.

(ii) Sliding friction: This friction which is produced when two objects in contact are in motion. It is lesser than static friction but more than rolling friction. In this type of friction irregularities of surfaces do not get enough time get locked with each other as objects are in motion.

(iii) Rolling friction: This friction is produced when two bodies are rolling on each other. Rolling movement of both objects does not allow the locking of irregularities, so it is the smallest friction among the three types of frictions.

71. The gases and liquids are called fluids. The friction exerted by fluids on an object is called fluid friction. The fluid friction is also called, drag.

Factors on which fluid friction depends :

(i) The fluid friction of an object depends on its speed with respect to fluid.

(ii) It depends on the shape of the object.

(iii) It depends on the nature of the fluid.