Question

from (kinetic friction) = coefficient * normal force, why is it that we can replace the normal force with mg when an object is sliding. I am trying to find the coefficient, but am stuck with the logic of the normal force resolving to mg?

Answer 1

since normal force is up and mg is opposite, these two vectors subtract and the difference is equal to m*a. Also, since there is no movement in the y-direction then there is zero acceleration. Therefore, the difference between the normal force and mg is equal to zero and solved for the normal force, which becomes: normal force=mg