Page 72 - Genius Kidz Prudence Learning Sc-8

So, you can easily make out that it is the
roughness or smoothness of the surface that
determines friction.

Cause of friction : Magnified view of surface
shows that every surface has some
irregularities on its base.

If irregularities of one surface get fitted into
the irregularities of the other surface, it is
called interlocking of irregularities. The
interlocking of these irregularities is
responsible for friction. The force required to Slim person moving Heavy person moving

overcome this opposition to cause motion is
Types of Friction
the frictional force. Since friction arises
because of interlocking of irregularities so (i) Static friction : Static friction is the friction
same force would be required to overcome between two non-moving surfaces or it is
these interlockings and that force is force of the friction between two resting surfaces in
friction. contact.
Static friction is the force that resists the
initiation of movement of objects.

The force that is needed to overcome static
friction is called static frictional force.
Rough Surface (With more irregularities)
Motion

Smooth surface (With less irregularities) Pushing force

Friction

Interlocking of irregularities between two rough surfaces
Static friction
Further, interlocking of irregularities between (ii) Sliding friction :The friction between two
two surfaces becomes more prominent with sliding surfaces in contact is called sliding
increasing weight of the moving body. This is friction. At the time of sliding interlocks are
the reason why slim person can move swiftly not formed but irregularities do strike each
and a heavy person moves slowly. other thus generating sliding friction.

pulling the spring.

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