What is the role of normal force in friction?

The role of normal force in friction is fundamentally tied to its direction and magnitude. The normal force acts perpendicular to the contact surfaces between two objects. This perpendicular force is crucial because friction is dependent on the normal force to determine its magnitude.

Friction arises from the interactions at the microscopic level between two surfaces in contact. The amount of frictional force that develops is proportional to the normal force: as the normal force increases, the frictional force that can act between the surfaces also increases. This relationship is often expressed in the equation: frictional force = coefficient of friction × normal force.

Understanding this, it becomes clear why the normal force does not lift the object off the surface; instead, it is a stabilizing force that enables friction to occur. If the normal force were to decrease significantly, such as when lifting an object, the frictional force would also decrease, allowing the object to slide or move more easily.

Hence, the role of normal force in friction is essential, and it indeed acts perpendicular to the contact surfaces.