How friction depends on surface area

In summary, friction is a complex concept that is often simplified in introductory mechanics courses. While the Coulomb model of friction is a good approximation for rigid objects with hard surfaces, it is not a fundamental law like Newton's laws or the ideal gas law. More advanced models take into account factors like the flexibility of objects and the atomic structure of materials, but these are best used in computer simulations rather than hand calculations. It is not possible to derive the simple expression of friction = μN from Coulomb's law for electric charges.
  • #1
s0ft
83
0
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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  • #2
Just look at the equations for the force of friction..nowhere is the surface area of the object included
 
  • #3
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.
 
  • #4
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.
 
  • #5
Just asking, would it be possible to derive the simple : friction = μN expression from Coulomb's law for electric charges?
 

1. How does surface area affect friction?

Surface area plays a significant role in determining the amount of friction between two surfaces. Generally, larger surface areas result in greater friction due to increased contact between the surfaces. This is because there is more surface area for the molecules of the two surfaces to interact with each other, creating a stronger bond and thus more resistance to motion.

2. Is friction affected by the type of surface?

Yes, the type of surface can greatly impact the amount of friction. For example, rough surfaces tend to have higher friction than smooth surfaces because there are more irregularities for the molecules to interact with. Additionally, different materials may have different levels of adhesion, which can affect the friction between them.

3. Does friction increase or decrease with surface area?

Friction generally increases with surface area. This is because as the surface area increases, there are more points of contact between the surfaces, resulting in more molecules interacting and creating a stronger bond. However, there are some exceptions to this, such as in the case of lubricated surfaces where the friction may decrease with increased surface area.

4. How does surface area impact the coefficient of friction?

The coefficient of friction is a measure of the amount of friction between two surfaces. In general, larger surface areas result in higher coefficients of friction. This is because the increased contact between the surfaces leads to more resistance to motion, resulting in a higher coefficient of friction.

5. Can changing the surface area affect the amount of force needed to overcome friction?

Yes, changing the surface area can impact the amount of force needed to overcome friction. As surface area increases, so does the amount of friction, meaning that more force is needed to overcome it. This is why larger objects often require more force to move than smaller objects with the same material and surface. Additionally, the roughness and type of surface can also affect the amount of force needed to overcome friction.

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