FRICTION

FRICTION
Friction is the property due to
which a force is setup at the
surface of contact of two
bodies preventing any relative
motion between them

TYPES OF FRICTION
SLIDING FRICTION
ROLLING FRICTION

SLIDING FRICTION
When ever a body slides or
tends to slide over the surface
of another body ,the friction
that is comes into play is called
sliding friction

TYPES OF SLIDING FRICTION
STATIC FRICTION
KINETIC FRICTION

STATIC FRICTION
It is the opposing force that
comes in to play when a body
tends to slide over the surface
of another body

KINETIC FRICTION
It is the opposing force that
comes into play when a body is
actually slides over the surface
of another body
Kinetic friction is also called the
dynamic friction

ROLLING FRICTION
The opposing force that
comes into play when a body
rolls over the surface of
another body .

LAWS OF FRICTION
The force of friction always acts in a
direction opposite to the direction of
relative motion
The maximum force static friction is
directly protional to the normal
reaction between two surface in
contact.


The nature of the limiting friction or the
maximum value of static friction
depends upon the nature or the state of
polish of the two surfaces in contact.
The limiting friction is independent of
the area of the surfaces in contact so
long as the normal reaction remains the
same.

COEFFICIENT OF STATIC FRICTION
 As we know that
fms ∞ R
 fms = µs R
 Where µs is the constant of proportionality and is
known as coefficient of static friction

DEFINITION OF COEFFCIENT OF STATIC
FRICTION
 fms = µs
R
 coefficient of friction defined as the ratio of max
static friction and the normal reaction

IMPORTANT POINT TO REMEMBER ABOUT COEFFICIENT
STATIC FRICTION
1) µs has no units
2) The value of µs depends upon the nature of
surface in contact
3) The value of µs is less than unity
4) The value of µs is never equal to zero

COEFFICIENT OF KINETIC FRICTION
 The force of kinetic friction is directly protional to
the normal reaction .
 fk ∞ R
 fk =µk R
 where µk is called the coefficient of static friction
 Hence coefficient of kinetic friction defined as the
ratio of kinetic friction to the normal reaction.

ANGLE OF FRICTION
The angle of friction is define as the
angle which the resultant of max
force of static friction and the
normal reaction makes with the
normal reaction.

ANGLE OF REPOSE
Angle repose defined as the
angle which an inclined plane
makes with horizontal when a
body placed on it just to starts
slide down over it

NUMERICALS
A block of 10 kg is pulled at a
constant speed on a rough
horizontal surface by a force of
20 N. calculate the coefficient of
kinetic friction given g=10m/s2

 A man whose shoes have leather soles and heels
is able to stand without slipping on a wooden
surface that makes an angle of 25o with the
horizontal. What is the max coefficient of static
friction for leather on wood? the value of tan 25o
=0.4663

 A wooden box is lying on an inclined plane. What
is the coefficient of static friction if the box starts
sliding when the angle of inclination is just 30o
 A body weighing 20kg just slides down a rough
inclined plane that rises 5cm in every 13 cm
along the plane .Find the angle of friction and the
coefficient of static friction ?

A cubical block rests on a plane of of
.Determine the angle through which the
plane be inclined to the horizontal so that
the block just slides down.
 A block slides down an incline angle 30
degree with an acceleration g/4 .Find the
coefficient of kinetic friction.

FRICTION

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FRICTION