Page 75 - Genius Kidz Prudence Learning Sc-8

sliding friction so of air between hull and the water reduces
usage of ball and the friction between the two.
bearings can reduce (v) By streamlining of moving bodies : Nature

t h e f r i c t i o n by has given birds and fishes streamlined
rep lacement o f bodies. So, on similar ground, bodies of
sliding friction by aeroplanes, rockets, cars are streamlined to
rolling one. reduce friction with air. Bodies of ships and
(iv) By use of a layer of boats are streamlined to reduce friction

air or avoiding direct with water.
contact : As seen in Ball and bearings Methods opted to increase friction :

the case of hovercraft introduction of layer Friction can be increased by allowing the
interlockings of two rough surfaces to entangle
up more closely, this can be achieved by
allowing the two surfaces to press together
more strongly. As in the case of car brakes,
brake pads press against moving parts of the

vehicle very strongly, causing the friction to
increase, resulting in the stopping of motion of
a vehicle.
Hovercraft

Tyres of racing cars are made smooth to reduce friction. Such tyres are called slicks. While the tyres of ordinary cars
have grooves to increase friction and hence their grip on the road.

! Friction is the force that resists the relative motion.
! Friction can be of four types– sliding, rolling, static and fluid friction.

! Friction is advantageous as it allows us to walk, stand, sew clothes and light up a matchstick, etc.
! Friction can be disadvantageous because it increases heat generation and power consumption, etc.
! Friction can be reduced by lubrication, polishing and by the use of ball and bearings.

EXERCISE
EXERCISE

1. Multiple choice questions.
(a) Static friction is:
(i) least (ii) maximum (iii) minimum (iv) All of these

(b) Drag is the frictional force between
(i) liquids (ii) solids (iii) gases (iv) gases and liquids

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