Think some good points were touched on about explaining anything in "layman's" terms. I always feel something is lost with any analogy, but analogies and "simplification" make things easier to understand to those that that don't have the proper background to understand the full equation. There is nothing wrong with simplification in my opinion as long as what is lost isn't significant, for example Newtons Laws are just fine for non-relativistic speeds. The problems occur when analogies or incomplete formulas are used to make new conclusions.

As for Reynolds numbers, the inertial vs viscous forces IS the actual definition of what a Reynolds number describes... it just isn't intuitively obvious to most what the heck that means. I think Banktoturn did a good job of explaining that better.

As for angular momentum, it must be conserved just like linear momentum. For a point mass, the area of an arc that a mass sweeps across in a interval of time must always be equal. Same basic rules apply to non-point mass but a little harder to explain. Easiest way to experience this is sit in a swivel chair and spin yourself up. Move your arms and legs in and out. If you ignore friction your rotational speed changes... that is conversation of angular momentum.