Ever wondered why it's so hard to walk with a cup of coffee without spilling? It just so happens that the human stride has almost exactly the right frequency to drive the natural oscillations of coffee, when the fluid is in a typically sized coffee mug. New research shows that the properties of mugs, legs and liquid conspire to cause spills, most often at some point between your seventh and tenth step.
Rouslan Krechetnikov and Hans Mayer, fluid physicists at the University of California at Santa Barbara, investigated the science of sloshing and calculated the natural frequency at which coffee sloshes back and forth when held in mugs of a variety of sizes, from a dainty espresso cup to a cappuccino behemoth.The Presurfer
