In contemporary physics, what is often considered the main cause of friction?

The primary cause of friction in contemporary physics is attributed to surface interactions. When two surfaces come into contact, the microscopic roughness of each surface leads to interactions that impede the movement between them. This roughness creates points of contact that resist sliding, which is a fundamental aspect of how friction operates. The nature of these surface interactions can be influenced by factors such as the materials involved, their textures, and whether there are any lubricants present.

While inertia, gravity, and molecular attraction can play roles in the behavior of objects and may indirectly affect friction, they do not serve as the direct mechanisms that generate the resistance to motion that we define as friction. Gravity, for instance, influences how much force is exerted between surfaces but does not directly create frictional forces. Similarly, while molecular attraction may have some impact at a microscopic level, it is the macroscopic interaction of surfaces that primarily accounts for friction. Thus, the idea that surface interactions are the main cause of friction is well supported in contemporary physics.