Types of Friction
The concept of friction was first given by Leonardo Da Vinci in 1519. He did the
systematic study of friction and the types of friction. This is the resistance which is acted
between the oppositely moving surfaces. This force is created when two surfaces are
trying to move or move which always resists the motion. This cannot be avoided in daily
life; for example, approx. 20% of gasoline is used to avoid the effect of friction in engine
of car or train. The tyres of car cannot be moved without friction because they do not
have grip for road. Even cannot walk without friction.
It is classified as static friction and kinetic friction. The static is acted between static
objects while the kinetic acts on the moving objects. Thus, the friction is also can be
described as electromagnetic force which is acted on atoms and molecules. It depends
on the contact force that is between the two surfaces. Here, we discuss about the
different types of friction that are rolling friction, sliding, static and fluid friction and their
examples.
Rolling Friction
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Rolling Friction occurs when an object rolls over a surface.It acts on the point of
the contact of the rolling object and the surface on which it is rolling. It tends to slow
down the rolling motion of the object. It is the combination of various other forces.
Causes of Rolling Friction

Deformation of the object

Deformation of the surface

The diameter of the wheels surface

The movement below the surface

Sliding

Surface adhesion

Surface properties

Material of the object

Temperature
The deformation of the object and the surface is the main reason of rolling friction. A
surface which appears to be smooth, on a molecular level is not so, it has many
irregularities present on it. Interlocking at molecular level is the reason of friction.
Figure: Showing interlocking between object and surface
If the wheel is soft, it gets deformed and hence leads to Plowing Friction which is
another form of Rolling Friction.
Figure: A diagram showing Plowing Friction
Rolling friction can also occur when an object rolls over a soft surface.
Example: When we ride our bike through soft dirt, it is difficult to do so because rolling
friction comes into action and hence opposes motion. It is very interesting to note that it
is easier to drive through soft dirt if the tire also has less air, this is because the traction
is increased which leads to improved driving.
Temperature also influences rolling friction and it is found to be inversely proportional to
friction. The Coefficient of Rolling friction is:
F = Crr N
Where,
F = force of friction
Crr= coefficient of rolling friction
N or W = weight of the object (wheel) in this case
(1) Rolling resistance is not directly dependent on the weight of the vehicle as obvious
in the above equation.
(2) When we apply brakes to any moving vehicle, rolling friction changes to kinetic
sliding friction.
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Sliding Friction
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Sliding Friction, also known as kinetic friction, takes place when an object slides
over another.For example, a notebook sliding over a table.
Figure: Showing Sliding Friction
The direction of the force is such that the relative slipping is opposed by the retarding
force (friction). For sliding friction formula:
Fk = Uk N
Where,
F = Sliding or kinetic friction
Uk= Coefficient of sliding friction
N = Normal reaction due to weight
The aim of sliding friction is to stop an object unlike rolling friction. It acts between
objects already in motion.
Kinetic friction is caused by chemical bonding between surfaces rather than interlocking
between them.
Figure: Graph showing Static and Kinetic Friction.
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Static Friction
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When two objects are not moving relative to each other, a force opposes or
resists the lateral movement of the objects and this force is called Static
Friction.It is the opposing force which comes into play when an object does not move
over another object, even when the force is applied to make it move.
The formula for Static friction is:
Fs = Fmax = Us N.
Example: When we push a heavy object and are unable to do so, we push it harder
and harder, after some time it moves suddenly and after its movement it's easier to
push it.
Here :
1. Because of Static friction we were unable to move the object.
2. When it moved, we had overcome the kinetic friction which was less then static
friction. If the coefficient of static friction is high, it means, a lot of force will be required
to overcome this static condition of the object and to get it in motion.
Figure: Man trying to overcome Static friction force
Thus, resistance encountered by a body in static condition while trying to move
under the action of an external force is called Static Friction. Static friction is equal
and opposite to the applied force.
Limiting friction is the maximum value of static friction and is also called Traction.
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Fluid Friction
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Fluid friction takes place when layers of any viscous liquid move over each
other. Viscosity is also called as thickness. Movement is inversely proportional to the
viscosity.
For example, water has lower viscosity than honey.
It is important to note that air is also a fluid made up of molecules. Fluid friction is
responsible for aerodynamic drag to a large extent.
Example: While driving a car, it experiences friction due to molecules present in air.
An ideal fluid does not offer any resistance to objects.
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Lubricated Friction
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When a layer of liquid exists between two solid surfaces, in such a situation, the friction
which exists is called lubricated friction.Lubrication is a technique by which a viscous
liquid is introduced in between two moving surfaces which aids for motion (smooth) and
also prevents wear and tear of the surfaces hence increasing their life span.
Skin Friction
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This occurs when solid body is moving over the fluid. The force which resists the
movement of a solid body through a liquid is calledSkin Friction. This directly depends
on the area of contact of the body with the fluid.
There are various ways to reduce it :
1. Improving the shape of the object
2. Reducing the surface area as far as possible
Friction Coefficient
Tension
More topics in Types of Friction
Rolling Friction
Sliding Friction
Static Friction
Fluid Friction
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