# Why doesn't friction depend upon area of contact? [duplicate]

Even though the pressure increases when the area of contact decreases why doesn't friction increase with decrease in area?

• Welcome to Physics! I've reverted an edit where you asked a separate interesting question; I thought the second one was different enough to stand on its own. – rob May 23 '20 at 5:54
• Does this answer your question? Dependence of Friction on Area – SarGe May 23 '20 at 6:13

## 1 Answer

Friction is directly proportional to the normal force acting on the body, i.e.;

$$f \propto N$$ where $$f =$$ friction force and $$N =$$ Normal force

$$\boxed {f = \mu N}$$

where $$\mu$$ is the coefficient of friction and depends upon the surface. We can also say that the normal force does not depend upon the area of contact and hence the friction.

Pressure, on the other hand is:

$$\boxed{P = \frac{F}{A}}$$

where $$F$$ is the force acting and $$A$$ is the Area of contact. Thus pressure depends upon the area of contact.