Laws of Solid Friction

Laws of solid friction:

• The frictional force between two surfaces opposes the relative motion between the layers.
• Frictional force is independent of the area of contact between the surfaces if normal reaction is constant.
• Limiting friction is directly proportional to the normal reaction in static friction.
• The value of limiting frictional force is always greater than any other kind of force.

Explanation of the laws of friction:
The frictional force between two surfaces opposes the relative motion between the layers because the welding effect is produced at the point as the pressure at the actual point of contact is very high.
When a body of smaller or larger area is brought in contact with the surfaces of another body, the limiting force measured is found to be constant. This proves that the frictional force is independent of area of contact.
The value of limiting friction is higher than any other type of frictional force because there is maximum inter-molecular force between the particles in limiting friction.