How friction depends on surface area

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Discussion Overview

The discussion centers on the relationship between friction and surface area, exploring whether friction is truly independent of surface area as commonly stated, or if there are conditions under which surface area plays a role. The scope includes theoretical considerations and models of friction, as well as potential implications for practical applications.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that friction is independent of surface area, referencing standard equations for friction that do not include surface area.
  • Others suggest that the traditional understanding of friction as independent of surface area may be an oversimplification, indicating that more complex models exist.
  • One participant highlights that the Coulomb model of friction, which assumes constant coefficients independent of normal force and surface area, is a simplification that may not apply in all scenarios.
  • There is mention of more intricate models of friction that take into account the flexibility of materials and atomic structure, though these are primarily used in computer simulations rather than analytical calculations.
  • A question is raised about the possibility of deriving the friction equation from Coulomb's law for electric charges, indicating a curiosity about the underlying principles of friction.

Areas of Agreement / Disagreement

Participants express differing views on the dependence of friction on surface area, with some supporting the traditional model and others advocating for a more nuanced understanding that includes additional factors. The discussion remains unresolved regarding the extent to which surface area influences friction.

Contextual Notes

Limitations include the potential oversimplification of the Coulomb model and the lack of consensus on the role of surface area in friction, as well as the complexity of more advanced models that are not easily applied in practical scenarios.

s0ft
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I'd read that friction is independent of the surface area of the bodies in contact. But somewhere in the internet I found that this explanation was just a good approximation and that friction actually depends on area. Can anyone explain a bit more on this?
 
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Just look at the equations for the force of friction..nowhere is the surface area of the object included
 
You can look @ http://zebu.uoregon.edu/1999/ph161/friction.html
and there you will find written friction is nearly or mostly independent of surface area. That must mean there is something more to it than just normal force and a constant.
 
s0ft said:
That must mean there is something more to it than just normal force and a constant.

There is a lot more to friction than what you learn in a first course in mechanics. The Coulomb model of friction (the static and dynamic coefficients of friction are constants and independent of the normal force, surface area, etc) is a simple model of friction that works pretty well for "rigid" objects with "hard" surfaces moving fairly slowly, in orher words the situation you have in lab experiments. It is also simple enough to use in hand calculations.

Some students seem to get the wrong idea that Coulomb's "law" of friction is the same sort of law as Newton's "law" of gravity or the ideal gas "laws". It isn't.

More complicated models of friction include the flexibility of the objects that are in contact, and possibly the atomic structure of the materials as well, but the only practical way to use those models is in a computer simulation, not setting up and solving problems by hand.
 
Just asking, would it be possible to derive the simple : friction = μN expression from Coulomb's law for electric charges?
 

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