FRICTION

FRICTION 

 friction may be defined as the force which comes into play along surface of contact between two body when one body move or tend to move over the surface of another body
  when force 'f' is applied to pull the upper body over the surface of lower body, the motion is rested on the surface this opposing force is called friction or force of friction

@ types of friction :-

           these are of two type

i) static friction :-

          it is the friction experienced by a body when it is at rest is known as static friction or the force of friction or the force of friction that come into the plain between the surface of the body before the actual motion starts is known as static friction

ii) Dynamic friction :-

          the force of friction that come into plain between the surfaces of the bodies after the actual motion starts is called dynamic friction
   the force of static friction is self adjusting force at mea it adjust its magnitude , so as to become adjectly become to applied force
for eg ;-
       a book lying on the table . if this book pulled with some force . it may not move at first , then we increase then applied force , it may move this time also in this way
             if the applied force is again increased in a sage will come when the body is just to ove at this stage friction is maximum
- static friction has any value between zero and limiting friction . once the force equal t over come limiting friction is applied body comes into motion and the friction express and this stage is known as dynamic friction

@ Limiting friction :-

           the maximum value of static friction which come into play when a body just begins to slide over the surface of another body

@ types of dynamic friction :-

         it is 2 type

i) sliding friction :-

                   the friction experience by a body when its slide over the another body
for eg :-
   the movement of piston in cylinder of an engine

ii) Rolling friction :-

          the friction experience by a body when it rools over the surface of another body the rolling of a cylinder over the ground the rolling friction is always less then the sliding friction because area of contact in case of rolling is much less than the area of contact in case of sliding of a body

@ Law of static friction :-

-  the force of friction in a director opposite to that in which the body tends to move
- under limiting equillibrium the magnitude of force of static friction is equal to the force which tends to move the body
- the force of friction depends is independent on the shape and the area of contact as well as normal reaction remain same
- the magnitude of limiting force of friction bears to the normal reaction between two surfaces . mathematically F/R= constant

@ Importance of fricton :-

         i) Useful effects of friction 

a) it is helpful in walking on the ground
b) safe driving of vehicle
c) Holding the nails into the wood in position

ii) harmful effect of friction :-

 a) it causes wear and tear of the moving parts
b) it causes loss of energy which turns into heat energy

@ Method of Reducing friction :-

- Polishing
- Lubricants
-  Avoiding moisture
- Proper selection of material

@ Normal reaction :-

          it has been experience that when a body lying on a horizontal plain or inclined surface is in equillibrium its weight act vertically downward threw it center of gravity. the surface upward reaction on the body the reaction is called normal reaction

@ Coefficient of Friction :-

         it is the ratio of limiting friction to the normal reaction between two surfaces in contact , it is denoted by meu which is = F/R. the value of meu is note the property single neutral but is is always combination of two surfaces in contact

@ Angle of friction :-

         the maximum angle between the normal reaction and the resultant of the force of limiting friction and normal reaction is called angle of friction

@ Angle of repose :-

          the minimum angle which an inclined surfaces makes with the horizontal . when a body placed on it on the point of moving down

@ Cone of friction ;-

               is defined as the right circular cone with vertex at the point of contact of two bodies ,axis in the direction of NR, semivertical angle equal to the angle of friction when the resultant of NR and the friction falls with in the cone of friction the forces acting on the body are not great enough to goes motion, this principle is used in self looking mechanism