The equation for friction between two surfaces is [math]F=μN[/math]. [math]N[/math] is the normal force between two the surfaces and the force of friction is directly proportional to that force. read more
The coefficient of friction is dimensionless, meaning it does not have any units. It is a scalar, meaning the direction of the force does not affect the physical quantity. The coefficient of friction depends on the objects that are causing friction. read more
So then youd have a coefficient of friction that would be expressed in so many pounds per ton. Bad practice, but its usefull on rare occasions where you'd rather not talk about a 0.0004 coefficient of friction, when what you care about is overcoming the 0.8 lbs of friction for every ton of load. read more