Consider a situation of the ring or a sphere rolling without slipping over a horizontal plane.In this case there is only one point of contact between
the body and the plane
The frictional forces developed between two surfaces in case described above is called rolling friction
Rolling friction develops between two surfaces when one body rolls over the surface of another body
We know that it is very difficult to pull a heavy metal box on a rough surface and if we attach four metal wheel to the box it becomes easier to move the box on the same surface
Thus resistance offered by the surface during rolling is relatively less than offered during sliding friction
This is because while rolling surfaces in contact do not rub each other
Rolling friction is negligible in comparison to the kinetic and static friction which are present simultaneously
In many parts of the machine where this type of friction is undesirable ball bearings(small steel balls) are generally kept between the rotating parts of the machines.This ways power dissipation during the motion can be reduced
(6) Methods to Reduce Friction
Friction can be reduced by the numbers of methods.Some of them are listed below
(a)Lubrication: when a lubricant is applied between the two surfaces in contact then a thin layer of lubricant is formed between the two surfaces resulting in
reduction in friction.Example of Lubricant Grease oil,graphite,compressed air
(b)Polishing : Irregularities of a surface can be reduced by polishing the surface smooth which results in reduction in friction
(c) Friction between the two surfaces can be reduced by using ball bearing between the two surfaces.Also sliding friction can be converted into rolling
friction which is much less then sliding friction
