[Piotrsko]

Take a big rock in the middle of a fast river. Somewhere down stream the flow is smoothed again but the rock is still creating drag which attempts to move the rock downstream as long as the river is flowing. Putting another rock behind the first rock and you get more drag, but maybe not twice as much total drag as the first rock even if the second rock is the same size or even bigger, mostly because the flow around the second rock had to slow down after the first rock. So drag is speed related.

A vortice in a headlight bucket can make the headlight bucket look bigger because it extends past the bucket and disturbs air flow outside of the bucket. Sometimes those vortices reduce the airflow speed hitting the windshield (or something else). Big second rock has reduced drag, so does the windshield. Sometimes you can fool flows into smoothness with shapes that dont look smooth. THAT is magic to me.

Another concept is that drag adds but doesn't subtract. Once you have it, it doesn't really go away, even after some distance. Second rock has visible effects in the stream for a good distance until the flow has had a chance to speed back up. You could build channels in the river to help re-direct and re smooth that flow, but I do not know how to do that, but I can do it just a little bit with wings and flaps because I know how to trick the air into flowing smoother. Most of the time I make things worse.

The difference between a car and the rock is what is moving to disturb the flow. The air is mostly still and the car moves, whereas the rock is stationary and the river moves.

I grok the learning difficulty. There are things in my head that I cannot share because the language portion goes on strike or makes me look foolish.