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We were discussing the importance of friction i.e. positive and negative effects of friction, classifications of friction and coulomb's law of dry friction with the help of our previous post.  

Now, we will be interested further to understand here few guidelines for solving frictional problems. We will see here few important points that we need to keep in mind during solving the problems related with friction. 

Guidelines for solving friction problems in mechanics

Laws of friction will be valid only at the moment when motion is impending. Impending motion refers to the state just before body surface starts to slip. 

The reaction force at the surface can be resolved into two forces i.e. normal and tangential. 

When the motion is not impending, the frictional force can be determined only by using the equilibrium equations. 

We need to start to solve the frictional problem by indicating the frictional forces as unknowns with suitable symbols f1, f2 etc.   

Unlike other free body diagram problems, any direction could not be considered for frictional forces. It should always be such that it opposes the motion. 

Analyse whether motion is impending or not. If motion is impending, replace f1, f2 etc with µs x Normal load. Otherwise, we will leave the unknowns as it is and will determine them using equilibrium equations. 

Frictional force reduces as motion commences because of the reduced meshing and adhesion of the surfaces. 

Friction coefficient will be dependent on the quality of surface of finish. 

Therefore, we have studied here the various guidelines for solving frictional problems. Further we will find out another concept in friction i.e. rolling resistance with the help of our next post.  

Do you have any suggestions? Please write in comment box and also drop your email id in the given mail box which is given at right hand side of page for further and continuous update from  

We will find out now the concept of rolling resistance in our next post.   


Engineering Mechanics, By Prof K. Ramesh  
Image courtesy: Google     

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