f-sub-K EQUALS *mu*-sub-K TIMES *N*

The force of kinetic friction is equal to the coefficient of kinetic friction times the normal force.

Kinetic friction, also known as sliding friction, is the frictional force exerted by a surface upon an object that is sliding along that surface.

**Pitfall Avoidance Note:** *mu*-sub-K
is not the frictional force. *mu*-sub-K is the coefficient
of kinetic friction. The value of *mu-*sub-K can only be a
pure number, a value with no units. The force of kinetic friction
does depend on *mu-*sub-K, but it is never equal to *mu*-sub-K.
It can't be. The quantity *mu*-sub-K does not even have
units of force.