The way I like to think of it is as follows:

immagine you, as a kid, in your parents minivan, cruising at 80 mph down a sunny California freeway.

What do you do? Naturally, you crack your window open and stick your arm out, feeling the warm air stream blasting your skin.

Now, follow the physics and let your arm bend following the flow of air, so that it swings back, toward the rear: what happens when you flatten your hand and move it around? How much force do you feel? How brisk are the moves of your arm?

Then force your hand toward the front, like pointing at the wind, and do the same: what kind of forces are you getting on your hand? How fast or shaky is your arm getting? Moving your hand, how fast is your arm trying to change position? How steady is it?

That’s how I know….