Independence of friction and area of contact

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Homework Help Overview

The discussion revolves around the relationship between friction and the area of contact between two surfaces, exploring whether friction is influenced by contact area or not.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are examining the principles behind friction, particularly questioning the independence of friction from the area of contact. Some suggest that while coefficients of friction remain constant, total friction may vary with contact area.

Discussion Status

The conversation includes differing viewpoints on the dependence of friction on contact area, with some participants providing reasoning related to pressure and local forces. There is an ongoing exploration of these concepts without a clear consensus reached.

Contextual Notes

Participants are discussing the implications of normal force and contact area in the context of friction, indicating a need for clarity on definitions and assumptions related to these variables.

prasanna
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Can anyone tell me why friction does not depend on the area of contact??
 
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Total Friction does depend on the area of contact. The coefficients of friction do not.
 
The short version is:
If two surfaces is pushed "hard" together they will tend to stick, and the local tangential force will typically be proportional to the PRESSURE acting locally.
The average pressure on the surface ought clearly be N/A, where N is the normal force, whereas A is the contact area.
The LOCAL tangential force (acting on a surface element "dA") can therefore, on average equal to kN/A*(dA), where k is a dimensionless constant.

Summing up the local frictions, gives us the total friction as:
F=k*(N/A)*A=kN
 
Thanks arildno!
 

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