Laws of Static Friction

Laws of Static Friction

1. Under static conditions, the friction force opposes tendency for relative motion between the two surfaces in contact and acts tangential to the surfaces.

2. The limiting static friction force, which is the maximum value of friction force, is directly proportional to the normal reaction between the two surfaces in contact i.e. 

where μs is the coefficient of static friction.

3. Limit force of static friction is independent of the area of the two surfaces in contact.

4. Limiting force of static friction depends on the nature and material of the two surfaces in contact.

Note: Friction force and normal reaction are always perpendicular to each other.