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ROLLING RESISTANCE OR ROLLING FRICTION: DEFINITION, EXPRESSION AND FACTORS CONTRIBUTING TO ROLLING RESISTANCE

We were discussing the importance of friction i.e. positive and negative effects of frictionclassifications of frictioncoulomb's law of dry friction and guidelines for solving frictional problems with the help of our previous post.  

Now, we will be interested further to understand here the basic concept of rolling resistance or rolling friction, definition of rolling resistance, formula or expression for rolling resistance and factors that contribute to the rolling resistance with the help of this post.

Rolling resistance 

Rolling resistance is basically defined as the force resisting the motion, when a body such as ball, wheel, automobile tyre rolls along the surface of another body. 

Deformation at the point of contact will develop the resistance to rolling. This resistance will be an entirely different phenomenon from that of dry friction. 

In analogy with sliding friction, rolling resistance will be expressed as a coefficient of rolling resistance multiply by the normal force. 

There will be no slipping or impending slipping in the interpretation of rolling resistance. 

Formula or expression for rolling resistance 


The expression for rolling resistance could be written as mentioned below 

Fr = c x W 


Where, 
Fr = Rolling resistance or Rolling friction (N) 
c = Rolling resistance co-efficient or co-efficient of rolling friction i.e. CRF 
W = Normal force (N) 

Rolling resistance co-efficient or co-efficient of rolling friction i.e. CRF is a dimensionless.  

Factors that contribute to the rolling resistance

Factors that contribute to rolling resistance are the deformation of the wheels, the deformation of the roadbed surface, surface adhesion, wheel diameter, speed, load on the wheel, sliding and relative micro-sliding between the surfaces of contact. 

For example, you can see that a rubber tyre such as automobile car will have higher rolling resistance on a paved road as compared with a steel railroad wheel such as a train wheel on a steel rail. 

Automobile car running on a road will have higher rolling resistance because its tyre wheel will be soft. On the other hand, train steel wheel running on rail track will have relatively lower rolling resistance as its wheel will be quite hard as compared with the tyre wheel. 

We must note it down here a very important point that rolling friction has the least value. Rolling resistance or rolling friction has led to the development of ball and roller bearings. 

You can see here the detailed post based on the basics of bearings. 


Therefore, we have seen here the basics of rolling resistance or rolling friction with the help of this post. We have also introduced here the bearings which is basically the result of research to reduce the rolling resistance. 

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We will find out "Wedge friction and self locking in engineering mechanicsin our next post.    

Reference:  

Engineering Mechanics, By Prof K. Ramesh  

Image courtesy: Google      

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