Features of the description of friction in introductory physics textbooks with a focus on the interlocking and the adhesion theories

Both the interlocking and the adhesion theories have contributed to the understanding of friction. Friction is a force that is not fully understood by us even today. In addition, each theory alone cannot explain the mechanism of friction completely because the detailed mechanism of friction is very complicated. However, current introductory physics textbooks only include adhesion theory. Also, in many cases, textbooks present approximate experimental results for friction as complete results. We can help students' understanding of friction by using other conflict theories rather than only one complete theory. We can also help students' understanding of friction by explaining, how the two complementary theories of friction were developed. In addition, we need to emphasize that the rules of friction are approximate results and that the rules have limitations because the rules only agree with simple models. This might give students an opportunity to pursue a modern understanding of friction.