Sandhya (1)

PRESENTED BY
SANDHYA V S
PHYSICALSCIENCE

FRICTION
Suppose you decide to ride a skate board
You push off the ground and start moving
According to Newton’s second law
of motion ,if no
other forces are acting
on your skateboard , you
will continue to move….BUT

The reason is that there exist a force
between the
ground and lower portion of the
skateboard, called
FRICTIONAL FORCE.

WHAT IS FRICTION
Friction is the force which opposes relative
motion
between two surfaces in contact with each other

What causes Friction
Even though a surface may look smooth, if you magnify the
surface it isn’t smooth.
Everything is made of molecules. The molecules come
together to make bumps. Some surfaces have molecules
that leaves large bumps and some leaves small bumps.
Micro welds occur when two bumpy surfaces are rubbed up
against each other they stick together.

Types of frictions
Static friction
Frictional force between two surfaces before there
is a relative force between the surfaces in contact.
Kinetic friction
It is the force of friction which calls in to play when
there is relative force between the surfaces.

Rolling friction
Rolling friction between two surfaces in contact is the force of
friction which calls into play when a body rolls over another.
Sliding friction
sliding friction is the force that opposes the motion of two
surfaces sliding past each other.

ADVANTAGES OF FRICTION
Helps us in walking conveniently. It save us from
slipping.
Helps us in writing on piece of paper.
Helpful in eating and drinking
Lighting a match stick by rubbing.
Nails and screws join two surfaces due to the
friction.
 we can not climb a tree.
Trains can run on the rails.
In fact life become impossible if there is no
friction in nature.


DISADVANTAGES OF FRICTION
Due to friction the whole energy given to a machine
is not converted in to useful work; a portion of
energy is wasted to overcome friction.This reduces
the efficiency of the machine. The energy used in
overcoming friction appears as heat. Moreover,
friction causes wear and tear of the moving parts of
the machine due to rubbing.

Thus
FRICTION IS A NECESSARY EVIL

TO INCREASE FRICTION
It is not possible to walk or drive through
muddy and slippery roads. For this sand and
gravels are spread to reduce friction
 Tyres of our vehicles also the soles of the shoes are
grooved.

Mountaineers also wear spiked shoe.
To overcome skidding along a slippery surface we adopt
measures to increase friction.

TO REDUCE FRICTION
Reduce the area of contact of two surfaces.
Making the surfaces as smooth.
Lubrication can reduce friction.
Using ball bearings.

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