The other day I was driving down the highway behind a Fertilizer Truck. It had a huge plastic reservoir of liquid fertilizer on the back, essentially a large cylinder lying on its side. The reservoir was not full and it was partially translucent, so I could see the fertilizer sloshing around in the cylinder. I reasoned (as anyone would I think) that to increase the stability of the truck--especially in the turns--you could simply fill the cylinder to the brim. That way you don't have all the sloshing. So I started thinking to myself, what dictates the "stability" of fluid? I thought it must relate directly to the surface area of the fluid. More surface area means more sloshing. But then again, the shape of the container might also affect the sloshing, because I think that a martini glass sloshes like crazy compared to an inverted cone-shaped container with equal surface area...doesn't it? I'm looking at a coworker's coffee mug right now, and its sides have a negative slope rather than a positive slope (looking at a cross-section of the mug in the positive x-axis direction...I know there's an easier way to say that but oh well). So the mug is well-designed for less sloshing! Right? But why? Can anyone point me in the direction for more information on fluid dynamics, and/or summarize what's most important for fluid stability/instability, container design or surface area, or something else? I'm perusing over the web page that follows this paragraph as I type, but I thought this may be a topic that someone out there would find fun. I think it's a neat topic because we intuitively know some things about fluids, even if we don't understand the equations or causal reasons behind it. I don't, and I'm curious. http://www.allstar.fiu.edu/aero/Flow2.htm Hey thanks guys & gals!