Which factor is the magnitude of friction related to?

The magnitude of friction is fundamentally influenced by the roughness of the contact surfaces involved. When two surfaces come into contact, their texture—whether smooth or rough—affects how easily they slide over each other. Rough surfaces tend to interlock and create more resistance to motion, thereby increasing the frictional force. Conversely, smoother surfaces may generate less friction due to reduced interlocking and less area of contact.

While temperature, weight, and humidity can have effects on how friction behaves in certain scenarios, the roughness of the surface is a primary factor in determining the baseline level of friction that exists between two objects. The characteristics of the material surfaces, particularly their roughness, dictate how they will interact when a force is applied to move one over the other.