Page 73 - Genius Kidz Prudence Learning Sc-8

The force that is needed to overcome It is for this reason that new design
sliding friction is called sliding frictional suitcases have wheels so that they can be
force. rolled on instead of sliding them.

(iv)Fluid friction : Fluids include air and water.
The medium that can flow is called fluid.
Friction exerted by a fluid is called as fluid
friction or drag. Force that is needed to
overcome fluid friction is called as fluid

Sliding friction frictional force.
Examples of fluid friction include :
(iii)Rolling friction : When an
object rolls over a surface (i) Aeroplanes need to overcome air friction
then the irregularities during flight, ships need to overcome
b e t w e e n t h e t w o friction due to water.
interlock. This generates (ii) Hair dries up in air due to air friction.
rolling friction. But in the
Factors affecting fluid friction include :
case of rolling motion the (i) Speed of the object : Higher the speed
area of contact is much Suitcase with wheels
greater will be the fluid friction exerted on
less as compared to sliding motion and the object.
static motion. So,
(ii) Shape of the object : Streamlined bodies
rolling friction < sliding friction < static
face less fluid friction.
friction.
(iii) Nature of the fluid : Viscous fluid as oil
The force that is needed to overcome
offers more friction as compared to fluids
rolling friction is called rolling frictional
of less viscosity.
force.
Activity 1

Identify static, sliding, rolling and fluid friction with the help of any simple practical application.
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Limiting friction is the friction that acts when the body is just about to move.

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