Does friction depend on area of surface of contact?

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Discussion Overview

The discussion centers around whether friction depends on the area of the surface of contact. Participants explore various aspects of this question, including theoretical models, practical examples, and the implications of different materials and conditions.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants argue that friction does not depend on the area of contact, citing the Coulomb model of friction where the frictional force is defined as the coefficient of friction multiplied by the normal force, which they claim does not change with area.
  • Others propose that friction is influenced by the microscopic bonds between atoms of the surfaces in contact, suggesting that a larger contact area leads to more atomic interactions and thus more friction.
  • One participant mentions that the deformation of materials can affect the contact area, indicating that softer materials may increase the effective area in contact, which could influence friction.
  • There is a discussion about the limitations of the Coulomb model, with some participants noting that it may not apply to all situations, particularly with materials that can form adhesive bonds.
  • Another participant acknowledges that while they believe friction depends on area, they struggle to reconcile this with the traditional formula that emphasizes normal force.
  • Some participants reference practical examples, such as car tires, to illustrate their points, noting that broader tires can provide better grip despite the traditional friction model.
  • There is mention of the coefficient of friction being variable depending on experimental conditions, such as surface deformation and temperature changes.

Areas of Agreement / Disagreement

Participants do not reach a consensus. There are multiple competing views regarding the relationship between friction and contact area, with some firmly supporting the idea that area affects friction and others defending the traditional Coulomb model.

Contextual Notes

Participants express uncertainty about the applicability of the Coulomb model in various scenarios, particularly regarding different materials and conditions. The discussion highlights the complexity of friction and the need for a nuanced understanding beyond simple models.

ank_gl
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dont have much time, ll make it quick

does friction depends on area of surface of contact??
i don't think it does:confused::confused:
 
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well actually, yes.
 
an example for this is seen in cars.When the area under contact is more, in tyres, the milage(kms covered per litre of petrol) of the car reduces as more friction acts on the tyre,thus resulting in the need of more power for attaining a particular speed.
 
exactly that's what came to my mind at first
but frictional force is coefficient of friction * normal force. mu is constant, normal force is m*g. neither of the three quantities change with using broader tyres, do they?? NO, they dont. so how frictional force depend on area.
 
Friction is due to the microscopic bonds forming between the atoms of two surface close together. The more area you have in contact the more atoms, more bonds, more friction.
It also depends on the amount of deformation of the materials - more pliant materials deform to out more surface are in contact. That is one of the reasons that inflatable tires are sued on cars and jewels are used in watches.
Finally it depends on the chemical nature of the two materials and the strength of the bonds it forms.
 
that i know, but how do you negate the fact that i talked about in post#4.
frictional force = mu*normal contact.
none of the two change by increasing the area.
practically speaking, true, cars with broader tyres have better grip, an example is formula 1 cars, but how, or more precisely, why??
 
In your post #4 you are not talking about friction, you are talking about the Coulomb model of friction.

Coulomb's model (or so-called law) works fairly well for in some situations. Because of the way mechanics is taught it schools, some people get the idea that it applies to every situation that could be described as "friction", but it doesn't.

It doesn't apply at all for many combinations of materials. For, example, if surfaces are coated with adhesive there can be a "friction force" even when the normal load is negative!

Car tyres are just one example where the Coulomb friction model isn't adequate to explain what you observe. And since Coulomb died in 1806, he certainly never thought about the friction of synthetic rubber on asphalt when he proposed his "law".
 
AlephZero said:
It doesn't apply at all for many combinations of materials. For, example, if surfaces are coated with adhesive there can be a "friction force" even when the normal load is negative!
well anybody can be considered as a join of two saperate bodies, therefore your concept of negative loading is plain stupid

AlephZero said:
Car tyres are just one example where the Coulomb friction model isn't adequate to explain what you observe. And since Coulomb died in 1806, he certainly never thought about the friction of synthetic rubber on asphalt when he proposed his "law".
so what is the law goverining friction which covers the term of area? just the point that coulomb didnt thought of this situation, doesn't make his law invincible. if a law is failing at a point, it should be scrapped or should be conditionalised.
as far as teaching of the law in school, we did study about the car example and DID use the same formula.
i am not trying to defend my point, i know that friction depends on area, but just this formula is not getting into my head. according to it, frictional force depends entirely on weight(normal force), not on area
 
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'mu' is not a universal constant of the materials but only constant for that experimental setup. Even then it varies if for instance the surface is able to deform under the normal force or if the material changes with temperature.
 
  • #10
hmmm that might be a possibility..
so the coefficient of friction depends on area of contact??
i very well know the fact that friction DOES depend on area, the microscopic bonds explanation being a good enough reason. i am having this debate with some of my friends & i am on the
"AREA affects FRICTION" side. i just didnt give the coefficient of friction varying, much thought
 
Last edited:
  • #14
kach22i said:
What?

Nothing about hovercraft in that link?:wink:

geez kach, you are mad for hoverthings! arent u??:wink::wink:
 

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