The transition from atomic stick-slip to continuous sliding has been observed in a number of ways. If extended contacts are moved in different directions, so-called structural lubricity is observed when the two surface lattices are non-matching. Alternatively, a "superlubric" state of motion can be achieved if the normal force is reduced below a certain threshold, the temperature is increased, or the contact is actuated mechanically. These processes have been partially demonstrated using atomic force microscopy, and they can be theoretically understood by proper modifications of the Prandtl−Tomlinson model.