Question

Which of the following are done to reduce friction?
a. Making grooves in the shoes, b. Polishing rough surfaces, c. Using wheels, ball bearings, d. creating an air cushion.
(a) a, b and c
(b) c and d
(c) b, c and d
(d) All of the above

Answer 1

Hint: The friction is inversely proportional to the polishing of the surface. If the surface is polished the friction will be less and vice-versa. The friction is restricted only. We will search for the presence of polish surface in the options and then, we will select the one which resonates to the question.

Complete answer:
Friction: It is a repulsion that gets activated when the object is accelerated with some velocity. If the surface is rough then, it clearly means that there is friction. For example if we take a slanted surface and we try to accelerate the pencil then we will find that it will take more time to reach the bottom of the surface in comparison to a polished surface.
By the term groove we mean a small cut or very little depression in a solid object. So, in the first part we see that making grooves means making small depressions under the shoes. This is basically done so that we do not slip while walking or running.
If we polish rough surfaces like furniture then, after applying polishing the surface of furniture, it gets smooth. This results in a slippery surface of the object which of course does not reduce friction.
Using ball bearings in the wheels of cars or any other vehicle is an important part of these. This is because it helps to join the wheel to its axle. This does create friction in the form of rolling type friction.
An air cushion is a cushion which is filled by air. This is used in many ways. Since, it forms a separation with air, so definitely it reduces friction.

Hence, the correct option is (c).

Note:
We can understand friction from the objects which are nearer to us. For example if we look at the tiles then we will find that the tiles inside the room on the floor are a little slippery with less friction as compared to the tiles that are on the floor of the bathroom. The shoes which are used by sports persons are made with greater friction so that the sportspersons run better and do not fall down. To increase friction we will make the surface more rough than before.