How the Edge of Our Galaxy Defies Known Physics

Just an off the wall thought about the outer portions of galaxies.
It reminds me of the playground toy merry go round, the further to the edge you are the more you feel it's force. 
Then again water spiraling down a drain does not appear to effect the outer edges of the liquid to the extent as it does near the center. 

I am definitely not a physicist but it seems both scenarios are similar in action but differ greatly in effect.
Could it be that water being around 800x more dense than air is the reason for this difference as the friction from its density reduces the effects significantly on the outer edges.

If so would this be a way to reasonably predict the densities of these unknown forces of matter by the energies that reach the outer portions of galaxies.

Please don't be to harsh I'm not a physicist or even close to it, just wondering about the relationships between centrifugal forces and densities of different things.

Edit 
After further thought on a merry go round the mass of ones body is probably related to the amount of energy one feels. If no one was on the merry go round while its spinning  the forces would be different. 
Same as the liquid except opposite, a mass in the spiraling liquid would seem to slow the forces.
So does this mean the accumulative mass in outer portions of galaxies are in direct relationship with the densities of the unknown dark matter or energies? Being that they spin differently some faster than others. Would this possibly aid in determining something about these unknown things.

Probably completely of the reservation on this but it's just a thought.