I learned that friction comes from the tiny crashes between the small bumps of uneven surface of each object. And I could make a rough guess about why heat is produced when two objects are rubbed together. Since friction is made by bumps(?) on the surface, the force you push downward(vertical to the surface),and the friction seems like it does not have to satisfy the linear equation such as
For conclusion, is the explanation of friction using the bumps right? And if it is, in what specific structure of the surface can they satisfy a tendency of linear equation even though the linear equation is just a simple mathematical concept?