Commentary:

Imagine a car is on a lift. The car is on, it has been put into drive, and someone is inside pushing the gas pedal to the floor. The tires are spinning rapidly on the axle. Now imagine touching one of the spinning tires. Ouch!

Now imagine the same scenario, yet the tire pops off the axle and rolls away, carried by its forward momentum, for thirty or forty feet to where you happen to be standing. Now imagine bending down and touching it as it approaches. It slows to a stop and impotently topples over onto its side. 

In the first instance, the rotation is tightly contained, powerful and controlled. In the second instance the rotation becomes decreasingly powerful and cannot be controlled once it has been seperated from the axle. 

It's not that momentum-based attacks are ineffective, it's just that the strong can always overcome the weak when both parties use momentum to fight. Yet, by mastering "contained spiral force" the "weak" can overcome the "strong." Master Hong could not lift heavy rocks, yet could send strapping youths sailing through the air.

You must become a gearbox with machine-like precision.