Friction depends upon area or not?

  • Context: High School 
  • Thread starter Thread starter Ahsan2011
  • Start date Start date
  • Tags Tags
    Area Friction
Click For Summary

Discussion Overview

The discussion revolves around the question of whether friction depends on the area of contact between surfaces. Participants explore theoretical explanations, personal experiments, and the complexities of friction in real-world scenarios, including the implications for different geometries and materials.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant asserts that friction is independent of the area of contact and depends solely on the coefficient of friction and the weight of the body, but questions this based on personal observations of different geometries affecting frictional force.
  • Another participant suggests that the coefficient of friction is material-dependent and proposes that variations in material or weight during experiments could explain differing results.
  • A participant references an idealized explanation of friction and highlights that real-world friction is more complex, citing a video demonstrating different sliding behaviors of blocks of varying sizes.
  • One contributor argues that the coefficient of friction may not be uniform across the contact surface, suggesting that larger surfaces could amplify variations in friction due to inhomogeneities.
  • Another participant emphasizes the complexity of friction, noting that multiple factors influence it, including normal force, velocity, and temperature, and criticizes the simplification of friction as solely dependent on area.

Areas of Agreement / Disagreement

Participants express disagreement regarding the role of contact area in friction, with some supporting the traditional view of independence from area and others challenging this notion based on personal experience and observations. The discussion remains unresolved with multiple competing views presented.

Contextual Notes

Participants acknowledge that the traditional explanation of friction may not account for all real-world factors, and there are limitations in the assumptions made in introductory physics texts. The discussion highlights the complexity and variability of frictional forces.

Ahsan2011
Messages
4
Reaction score
0
My books say that friction is independent of the area of contact, but only depends upon the coefficient of friction and the weight of body. but well according to my science, there is something wrong with it. because you observe, take same masses but different geometeries for example rectangular area of contact and other having cubic area of contact. then what actually happens the coefficient of friction doesn't remain same i did it in my home. frictional force comes out to be greater. what's this?
if it does not depend upon area of contact why we have wheels?
please some body help me
 
Physics news on Phys.org
The coefficient of friction depends only on the material of the contact surfaces. I suppose when you did some experiments with different geometries the material was different too (and maybe the weight too).

Another factor would be the height of the surface, theoretically height should be zero but in reality the objects have some height. This might alter the kinetic behaviour of the object as you apply some force to it and making it to rotate instead of just going forward and thus making you think that the friction is different.
 
Ahsan2011 said:
My books say that friction is independent of the area of contact.
That's an idealized explanation. In the real world friction is more complicated than that. A 4:35 into video #2 at the website below, 4 small blocks of different sizes on a flat sheet are shown to start sliding at different tilt angles, with the smallest block sliding last.

http://www.gyroscopes.org/1974lecture.asp

In the case of tires, maximum static friction force does not increase lineary with normal force, this effect is called load sensitivity:

http://en.wikipedia.org/wiki/Tire_load_sensitivity
 
rcgldr said:
That's an idealized explanation. In the real world friction is more complicated than that. A 4:35 into video #2 at the website below, 4 small blocks of different sizes on a flat sheet are shown to start sliding at different tilt angles, with the smallest block sliding last.

http://www.gyroscopes.org/1974lecture.asp

I think this happens because of friction coefficient not being exactly the same but varying across the contact surface. The greater the surface , the greater the result of this inhomogenity will be.
 
Friction is not a simple or fundamental force by any means. There are different mechanisms behind frictional force which grow or weaken depending on many factors (normal force, velocity, lubrication, materials, temperature, area, etc. etc) and even then not all of them are understood.

Therefore, saying that friction does not depend on surface area is a gross oversimplification at best. However, for one paragraph in an introductory physics book, in a specific case with many assumptions, this explanation of Friction = normal force x coefficient of friction appears to be adequate. Just be aware that this "coefficient of friction" can change, morph, shift, curve, or even reverse depending on many factors.

It's kind of like explaining a woman with the formula "Woman = Human x coefficient of womanly behavior". It's great, but it's meaningless without knowing what the "coefficient of womanly behavior" is, and it can be ANYTHING.
 
Last edited:

Similar threads

  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 35 ·
2
Replies
35
Views
6K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 10 ·
Replies
10
Views
2K