Factors affecting friction:
(i) It depends on the nature of surfaces in contact.
(ii) It is more between rough surfaces and less between smooth surfaces.
(iii) It depends on how hard the two surfaces press together.
(iv) It is independent of the area of contact.

Friction may be reduced in the following ways:
(i) Polishing the surface: We polish the rubbing surfaces to reduce their unevenness and make them smooth.
(ii) Lubricating the surface: To reduce friction in order to increase efficiency when oil, grease or graphite is applied between the moving parts of a machine, a thin layer is formed there and moving surfaces do not directly rub against each other. These substances are lubricants which reduce the friction.
(iii) Using wheels and ball bearings: By using wheels and ball bearing we convert sliding friction into rolling friction. This reduces friction between the two contact surfaces and helps us to save energy, effort and time.
(iv) Streamlining: Objects are given special shapes, such as streamlined body to aeroplanes. Their bodies shapes make them lose less energy in overcoming friction. Hence, all vehicles are designed to have shapes that reduce fluid friction.

Firstly, hold a pencil or pen. Now, put it on a table. Slightly push the pencil and see how much distance it covers. Put the marking of the point where the pencil stops after covering the distance. Now spread polythene on the same table. Now, again hold the pencil and put it at the same initial point. Now, push the pencil slightly and let it stop on its own as done earlier. Now, mark the point where the pencil stops. Notice the difference in the distance. In second chance, the pencil has covered more distance. This means it had to face less friction in second attempt. It shows that smoothness of the surface reduces friction.

(a) She turned her car towards the ploughed field to protect herself from an accident.
(b) Since, the car moved from road to the ploughed field due to which the force of friction between the tyre and the ground surface increases suddenly. Because the large amount of irregularities reduces the movement of tyre. Thus, the car came to a rest.
(c) The values displayed by Shradha are intelligence and awareness.

(a) Since, the player rub his hand due to which the palms become warm which absorb the moisture from the surface and make the surface rough. So, due to roughness of hands, the ball may get a better grip between the hands and does not slip.
(b) Since, the player makes the palm surface oily. So, the number of irregularities decreases and the surface becomes smooth. So, the ball slips off easily from the hand.
(c) As, teacher wants to teach the students through easy example. So, this act of teacher shows the experience and ideality of teacher.

When a fine powder sprinkled on the carrom board and a few drops of oil are poured on the hinges of a door, the door moves smoothly. A cycJe or a motor mechanic some times uses grease between the moving parts of the cycle. In all the above cases, our try was to reduce friction in order to increase efficiency.
Also, interlocking of irregularities is avoided to a great extent due to which the movement becomes smooth. The substances which reduce friction are called lubricants. In some machines, it may not be advisable to use oil as lubricant. There is an air cushion between the moving parts, that is used to reduce friction.

While rubbing with sand paper, more frictional force is produced between the layers of metal sheet and sand paper which causes more force on dust particles and they are removed easily, so it will shine more. But in case of ordinary paper, the force of friction is not sufficient to remove all the dust, so it will shine less in this case.

As friction opposes the relative motion between the two surfaces also produce heat. So, when we rub our hands together vigorously for few minutes, we feel hotness when we strike a matchstick against the rough surface due to which it catches fire. In machineries also, heat is produced due to friction as the machine parts rub against each other.

(i) The player rubs his hands due to which the palms become warm which absorb the moisture from the surface and make the surface rough. So, due to roughness of hands, the ball may get a better grip between the hands and does not slip.
(ii) If the player makes the palm surface oily, the number of irregularities decreases and the surface becomes smooth. So, the ball slips off easily from the hand.
(iii) As, teacher wants to teach the students through easy example so this shows that the teacher is experienced and ideal.

Following examples show that the friction produces heat:
(i) Warming of our palms when we rub them.
(ii) Rubbing sticks together to produce fire.
(iii) Warming of the parts of a machine when it is operated.