# Static Friction

## Static Friction

Friction is a force which comes into existence when two bodies in contact have relative motion or tending to have relative with respect to each other and oppose the motion.

Types of Friction:

There are three types of Friction:

1. Kinetic Friction
2. Static Friction
3. Rolling friction

What is a Static Friction?

The frictional force which exists between the two surfaces which are at rest or which are on the verge of relative motion with respect to each other is called the static friction.

Laws of Static Friction:

Limiting static friction between any pair of dry unlubricated surfaces is independent of apparent area in contact.

Limiting static friction between any pair of unlubricated surfaces depends on nature and material of the surfaces in contact.

Limiting static friction between any pair of dry unlubricated surfaces is directly proportional to the normal reaction.

If Fs is static friction and R (N) is a normal reaction.

Fs α R

∴ Fs = μs R

Where,

μs = Coefficient of Static Friction.

∴ $${{\mu }_{s}}\,\,=\,\,\frac{{{F}_{s}}}{R}$$.

The coefficient of static friction is defined as the ratio of the limiting static friction to the normal reaction.