So, years ago I had a similar question and Dan Ebberts answered it, but I can't find the expression and I don't have the AE project anymore. So let's try this again...
Imagine you've got a piece of fabric attached to the end of a pole (like a streamer). When you move the pole to your left the streamer flows (is blown by wind, whatever) out to the right and vice/versa (trailing behind the movement and speed of the end of the pole). Everyone with me so far?
So when layer A moves left or right, layer B "flows" behind it, affecting it's rotation to do so (its anchor point attached somewhere on layer A).
When layer A comes to a stop, layer B, would rotate back down to 0 (or whatever it's "resting" rotation value is). Ideally it would ease back in to that "resting" rotation.
The faster layer A moved, the quicker layer B would "flow" up in it's rotation (maybe with a little wiggling as if a breeze for good measure)
Does this make sense?
What would be the best way to do this? I've got a lot of little pieces and I'm hoping not to animate it all by hand.
Julius Caesar and the Roman Empire couldn't conquer the blue sky.