# B Friction and area

1. Sep 19, 2016

### Amru123

Friction is independent of area of surfaces in contact as long as the normal reaction remains the same.I agree that it does not depend and so says it's formula but the condition that it does when the normal reaction remains same looks odd to me..Can someone help me out to understand this?

2. Sep 19, 2016

### Staff: Mentor

What seems odd to you about it?

3. Sep 19, 2016

### Amru123

I can't see the connection between how the "remaining same of normal reaction" makes friction become dependant on "area"

4. Sep 19, 2016

### Staff: Mentor

Who says that the friction force depends on the area?

5. Sep 19, 2016

### Amru123

Oh my god! You are misunderstanding my question.I was reading a book at a neighbourhood library when I came across this statement "Force is independent of area of surface of contact except when the normal reaction remains the same" Which clearly means normal reaction makes force become dependant.Do you get what I mean? If you don't believe in the statement I mentioned,Kindly look it up.It's true but I can't understand how it could be.Do help me gain some knowledge about it if you get to know it.Thanks in advance

6. Sep 19, 2016

### Staff: Mentor

Are you sure that's what you read? That's a puzzling statement.

In the 'standard model' of friction (where F = μN), the friction force does not depend on surface area of contact. Period. It does depend on the normal force pressing the surfaces together.

7. Sep 19, 2016

### Staff: Mentor

No. Is this the exact quote? Maybe there is an example problem associated with this?

8. Sep 19, 2016

### lychette

frustrating, isn't it?

9. Sep 19, 2016

### Nidum

Not a very clear piece of technical explanation but essentially correct .

There are situations where the area of surfaces in contact determines the normal reaction . An example of this would be a simple sliding rectangular slab of constant thickness . The bigger the sliding contact area becomes the heavier the slab becomes and the bigger the normal reaction becomes .

Last edited: Sep 19, 2016
10. Sep 20, 2016

### A.T.

Which is it?

Last edited: Sep 20, 2016
11. Sep 20, 2016

### Amru123

It's the former."as long as".Except is not right.Just now referred a website.Kindly bare my blunder.