What is the formula for the laws of kinetic friction?

The laws of kinetic friction are,

1. The force of kinetic friction always acts in the opposite direction to which body is moving.
2. The force of kinetic friction remains constant for moderate speed but it decreases with an increase in speed.
3. Magnitude of kinetic friction has a constant ratio to normal reaction between two surface. The ratio of kinetic friction is slightly less than that in case of limiting force of static friction.
4. The coefficient of kinetic friction is independent of the area and shape of the contacting surfaces.

The formula for law of kinetic friction is given as,

F_K = µ_k N ——— where F_K =Force of kinetic friction, µ_k= coefficient of kinetic friction and N=Normal force

The formula for coefficient of kinetic friction is given as,

µ_k = F_K / N