When a glass of wine is oscillated horizontally at 4Hz, the liquid surface oscillates calmly. Butwhen the same amount of liquid is contained in a cylindrical mug and oscillated under the sameconditions, the liquid starts to oscillate aggressively against the container walls and results in sig-nificant spillage. This is a manifestation of the same principles that also cause coffee spillage whenwe walk. In this study, we experimentally investigate the cup motion and liquid oscillation duringlocomotion. The frequency spectrum of each motion reveals that the second harmonic mode ofthe hand motion corresponds to the resonance frequency of the first antisymmetric mode of coffeeoscillation, resulting in maximum spillage. By applying these experimental findings, a number ofmethods to suppress resonance are presented. Then, we construct two mechanical models to ratio-nalize our experimental findings and gain further insight; both models successfully predict actual hand behaviors… More here.
To quote the excellent Steve Litchfield on Twitter- ‘Wow that's a lot of maths to explain something that most people will know instinctively 8-)’
I’m struggling to find a reasonable point where this amount of research could not be used more wisely on something more important.