Derivation for Friction in Brakes

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The discussion focuses on deriving the expression for frictional resistance in block brakes, emphasizing the need for clarity in the derivation process. The user expresses confusion over reference materials that assume friction produces torque in the same direction as the drum's rotation, questioning the validity of this assumption. They highlight that if both forces acted in the same direction, the drum would never stop rotating. Ultimately, the user seeks a comprehensive explanation of the derivation to resolve their confusion. The thread concludes with the user indicating they have found the answer to their question.
plutamech
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Homework Statement


Derive the expression for frictional resistances in block brakes.Use standard symbols to denote required parameters.


Homework Equations





The Attempt at a Solution


My actual problem is the fact that I have checked 2 reference books, both have derived the expression assuming the friction produces a torque in the same direction of rotation of the drum.There is no explanation why this has been done.
If these 2 forces(friction and force of rotation) were to produce torque in the same direction then I suppose the drum should never stop its rotation, so what is the actual derivation with explation?
Kindly Help..
 
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I have got the answer to my question.
Thank You Physics Forums.
 

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