Kinetic friction not working?

I recently have been trying to see if the physics were working correctly. I wrote a script that would apply a force for one second, then take the velocity after one second. Using impulse-momentum I see that the kinetic friction on the physic material is not working. I'm just sliding a box across the floor (both surfaces have the same k.f. coefficient). Any ideas why the k.f. coefficient doesn't work? (static is zero just to be safe) Any clarification on how to use it would be appreciated thanks.