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OVER VIEW
• FRICTION
• CAUSE OF FRICTION
• EFFECTS OF FRICTION
• FACTORS AFFECTING FRICTION
• TYPES OF FRICTION
• FLUID FRICTION
• ADVANTAGES OF FRICTION
• DISADVANTAGE OF FRICTION
• REDUCING FRICTION
• INCREASING FRICTION
 FRICTION
• If we switch off the engine of car it will stop
after moving a certain distance . It means that
some retarding force is acting on the car
which stops it. The force opposing the motion
of the car is called “ force of friction “.
• The frictional force is tangential (a force that acts on a
moving body in the direction of a tangent to the curved path of the
body)tothe surface in contact and always in a
direction opposite to the direction of motion
of the object .
• Frictional force is a force opposing the relative
motion between two surfaces which are in
contact with each other .
• The force of friction arises due to the
interlocking of irregular projections on the two
surface and is called “ force of contact ”.
 CAUSES OF FRICTION
• The causes of friction are molecular adhesion(the attraction
between the molecules of two different surfaces) ,surface
roughness ( the measure of the finely spaced micro-
irregularities on the surface texture) and the plowing effect(
When one or more of the materials are relatively soft, much
of the resistance to movement is caused by deformations or
a plowing effect.

Every object has a rough surface, though the surface may

appear to be smooth to the naked eye. But when we observe
through a microscope, we find that the surfaces of all the
objects have rough edges. Some of the particles on the
surface of objects are in form of tiny hills and valleys. When a
body is pulled over another, these tiny hills and valleys
present on both the surfaces in contact get entangled with
one another .
Friction occurs whenever two bodies that are in
contact move or tend to move with respect to each
other . It depends on the surface of contact of
bodies. Microscopic examination of surface of
various objects reveals that all the surface have
irregularities.
when two surface slide over each other , the
irregularities of these surface interlock with each
other . This interlocking oppose the motion
between the surface in contact and give rise to
friction .
The force of friction is basically caused by the
interlocking of the irregularities between the two
surfaces that are in contact . when sufficient force is
applied, the interlocks break and the body moves .
 EFFECTS OF FRICTION
Friction oppose motion . It prevents a
stationary object from moving . It also slows
down and stops a moving object .
Friction result in wear and tear of the surface
in contact. Friction between tyres of a vehicle
and road causes tyres to wear away.
Friction produces heat . In winters , we rub our
hands together to keep them warm. The heat
is produced due to friction .
 EFFECTS OF FRICTION
Friction oppose motion . It prevents a
stationary object from moving . It also slows
down and stops a moving object .
Friction result in wear and tear of the surface
in contact. Friction between tyres of a vehicle
and road causes tyres to wear away.
Friction produces heat . In winters , we rub our
hands together to keep them warm. The heat
is produced due to friction .
 FACTORS AFFECTING FRICTION
1. Nature of surface : A rough surface has more
irregularities than a smooth surface. This suggest
that the rough surface shows greater resistance
to the motion , that is greater friction . A rough
surface offer greater friction than smooth
surface.
2. Weight of an object : A heavy object placed on a
given surface will press harder into irregularities
than a light object. so, there will be greater
resistance to motion , than is greater friction .
this is why it is difficult to move heavier things.
3. Area of contact
Friction is independent of the area of contact
between two surfaces.The level of interlocking
decides the amount of friction between two
surfaces, but the level of interlocking is entirely
dependent on mass of the body . so, if more
the mass, more the intensity of interlocking ,
thus more is the friction . That is why, friction is
independent of contact area .
 TYPES OF FRICTION
1. STATIC FRICTION :
The friction acting between the two surface which are
in contact and placed at rest is called the static
friction.
1. LIMITING FRICTION
when the force applied on the stationary object is
gradually increased, a stage comes when the object
just starts moving. The maximum force required to
make the object move on the surface of other objects
is called limiting friction.
The object either slides or rolls on the surface of other
object . This gives rise to sliding friction or rolling
friction.
The force of friction acting between two bodies, when
one body is moving upon another body with a uniform
velocity is called dynamic friction . It includes sliding
friction and rolling friction .
3. KINETIC OR SLIDING FRICTION
The friction that exists between the two surfaces when
they are in contact in which one of them slides on the
surface of another is known as sliding friction .
when an object has started moving , the irregularities
do not get enough time to interlock. so a smaller force
is needed to keep it moving compared to the force
needed to move it from rest . Thus , sliding friction is
smaller than static friction.
Kinetic friction is smaller than the limiting friction .
4. ROLLING FRICTION
The frictional force that exists between the two
surfaces when a body rolls over the other is called the
‘rolling friction’
Rolling friction is smaller than sliding friction
static friction > sliding friction > rolling friction .
FLUID FRICTION
It has been found that fluids (liquids and gases)
also offer resistance to the motion of objects
moving through them . The resistance offered
by fluids is called fluid friction or drag .Fluid
friction on an object depends on the shape of
the object , speed of the object and nature of
the fluid. To reduce drag, a body must posses a
streamlined shape .
Drag due to water
The outer bodies of ships, submarines and
boats are made streamlined so that they
experience minimum amount of friction while
moving through water .
The body of fishes are also streamlined to
reduce drag due to water .
A swimmer streamlines his body while
swimming .
Drag due to air
The bodies of airplanes and automobiles are
also streamlined so that the air offers least
possible friction .
The shape of birds are evolved in such a way
that they can fly effortlessly in the sky .
ADVANTAGES OF FRICTION
We would not be able to walk if there had been no
friction between the soles of our shoes and the ground.
If there had been no friction, the wheels of a car will
instead of rotating and stop moving . For that we have
to increase the friction by making the tyres corrugated
to get better grip of tyres on the road. also the friction
is increased .
When brakes are applied, the vehicle stops due to the
force of friction between the brake lining and the drum
In the absence of friction , we cannot write on a
blackboard with a chalk stick because the chalk stick will
slide off the board without leaving any mark on the
board .
DISADVANTAGE OF FRICTION
1. Wear and Tear : The soles of our shoes and tyres of vehicles wear
out due to friction. It also causes wear and tear in the moving
parts of machines.
2. Wastage of energy : A lot of energy is wasted to overcome the
force of friction while initiating a motion in stationary objects.In
the absence of friction, we can avoid the wastage of energy.
3. Increase in fuel consumption: Automobiles and engines consume
more fuel to overcome the energy loss due to friction.
4. Production of unwanted heat : Friction causes unwanted heating
of the moving parts of machines. This leads to the wastage of
useful energy as heat. Also excessive heating can damage machine
parts.
5. Production of unnecessary noise : Friction is responsible for the
unnecessary production of noise in many machines.
 REDUCING FRICTION
1. By using lubricants: friction increases as the roughness of the
surface increases. Lubricants fill the fine pores and gaps between
contact surfaces and reduces friction
2. Polishing surfaces: It makes the surfaces even and hence
reduces friction
3. By using ball bearings: Rotating machines can be mounted on
ball bearings. Rolling friction is lesser than sliding friction
4. By streamlining: streamlining reduces the area of contact and
thus reduces friction.
5. using soap solutions : soap solutions are slippery in nature . They
are used to reduce friction in high speed cutting and grinding
machines , so that not only friction is reduced , but the heat
produced during the processes is rapidly taken away by the water
present in the soap solution .
 INCREASING FRICTION
Friction is a necessary evil. In some cases, we might want to
reduce friction but in some cases, we need to increase
friction. we look at 4 ways by which we can increase friction
and look at their real-life applications.

Higher friction may be required in applications for resisting

motion or for adhesive kinds of applications. For example, in
real-life applications like brake pads, sticky pads, adventure
vehicle tires, etc we need to increase the friction for better
efficiency. Friction can be increased by various methods like
texturing, pressure, sliding, etc.