I should stop complaining about air resistance, but I can't help myself! I am teaching this semester from Kibble & Berkshire, and in Chapter 3 there are problems about air resistance that use speeds of around 100 meters per second and an atmospheric drag law that is proportional to velocity to the first power. I don't think there is any physical system that could have these properties: If you are small enough to have viscosity matter, you can never go 100 meters per second. Well, I guess molecules can go that fast, but (a) that isn't what the authors have in mind, and (b) molecules aren't really well described by continuum mechanics!
