Which of the following statements about the coefficients of static friction μs and kinetic friction μk for a given pair of dry surfaces is most accurate?
a) μk is always greater than μs because it takes more force to keep an object moving than to start it.
b) μs equals μk only when the normal force is sufficiently large.
c) μs is always greater than μk for a given pair of dry surfaces.
d) Neither μs nor μk depends on the materials; they depend only on the contact area.