What causes friction and how does it affect motion?

Answer 1

Tiny, or even microscopic irregularities in the surface of a material can mesh with the irregularities of some other surface, almost like the teeth of some randomly designed gear, and thereby prevent the effortless slide of one material across the other; that is the cause of friction. Friction affects motion in the sense that it enables objects to exert force on other objects through a rubbing type of contact, and force can create motion. Walking is a classic example of this phenomenon. You can propel yourself forward because of the friction between your shoes or feet and the ground or floor upon which you walk; without friction your feet would just slide. Of course, it is possible to use sliding as a means of movement as well, which we see in ice skating. But walking requires friction.