Final answer:
Friction is mainly affected by the surface roughness and the normal force (related to weight), which are represented by the coefficients of static and kinetic friction multiplied by the normal force in frictional force calculations.
Step-by-step explanation:
Friction is a force opposing motion between surfaces and two primary factors affect it: surface roughness and the normal force (related to weight).
Firstly, the roughness of the surfaces in contact contributes to friction due to microscopic interlocking, which requires more force to overcome when surfaces are moved against each other. Secondly, the normal force acting on an object—the force perpendicular to the contact surface—has a direct impact on frictional force, as seen in the formula f_s ≤ M_s N for static friction and f_k = M_k N for kinetic friction, where M_s and M_k are the coefficients of static and kinetic friction, respectively, and N is the normal force.
Thus, if the weight of an object increases, which effectively increases the normal force, the frictional force also increases. Answer option B, roughness and weight, correctly identifies the two main factors that affect friction in the context of this question.