Amateur Aerodynamics

Continuing this series of posts , now we'll look at a more practical--and more popular--fallacy. Waxing Your Car Does Not Reduce Its Drag The claim: Clean and wax your car’s paint and the air will slip smoothly past it, reducing drag. This screenshot comes from--surprise!--a website for a carwash chain. There you have it; Internet wisdom at its finest ("we agree, so this must be true"). The reality: This one pops up on forums and online articles all the time. Unfortunately, it is a misconception that seems like it should be true: if fluid/air flows past the car body, making that body more “slippery” by waxing it should help the air move past more easily, right? Wrong.   What we’re dealing with here is a fluid boundary or “interface.” Interfaces can occur between fluids and solids or between different fluids (think of an oil slick floating on water or better yet, wind rushing over the open ocean; these are both examples of fluid interfaces). At these interfaces, strange, n