Coefficient of Kinetic Friction Equation

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Friction is very essential for our daily life and for mechanical purposes. It plays very important role in solving the various
problem in machinery and in other field of science.
Kinetic friction are of two types:    
  1.       Translational  kinetic friction  
  2.       Rolling kinetic friction.

Translation kinetic friction-  It acts when the body slides over another body or surface.  And it is generally represented by  Fk 
and the coefficient of friction is µk.
Rolling kinetic friction:    when the body undergoes rolling motion then friction involves is called the rolling friction. And the
coefficient of friction is called  µ r.

                                                       Fk   >    Fr       consequently              µ r      <      µ      

                                         and       Fk     =      µk  N      similarly           Fr   =      µ r N

Coefficient of friction tells how much fraction of the Normal force the friction is. The normal force is always greater than
kinetic friction. So, the coefficient of
Kinetic friction is always a very small number. And for the rolling friction it is even more less number.
Cause of rolling friction
When a body roll on a level track, the area of contact is very small.  Therefore, the pressure exerted is very large. This causes a

depression in the surface below and a   mount or bump in front.  Adhesive force between the surfaces causes the Rolling

  friction. These forces act between different surfaces.
For example, wood on floor, steel on  iron wheel on road etc.
 Rolling friction is the force that slows down the motion of rolling wheel on the floor.


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