Walking with coffee: Why does it spill?

Phys. Rev. E 85, 046117
volume 85, issue 4, pages 046117
Published 26 April 2012
DOI: http://dx.doi.org/10.1103/PhysRevE.85.046117

H. C. Mayer and R. Krechetnikov

Department of Mechanical Engineering, University of California, Santa Barbara, California 93106, USA

Abstract

In our busy lives, almost all of us have to walk with a cup of coffee. While often we spill the drink, this familiar phenomenon has never been explored systematically. Here we report on the results of an experimental study of the conditions under which coffee spills for various walking speeds and initial liquid levels in the cup. These observations are analyzed from the dynamical systems and fluid mechanics viewpoints as well as with the help of a model developed here. Particularities of the common cup sizes, the coffee properties, and the biomechanics of walking proved to be responsible for the spilling phenomenon. The studied problem represents an example of the interplay between the complex motion of a cup, due to the biomechanics of a walking individual, and the low-viscosity-liquid dynamics in it.

http://journals.aps.org/pre/abstract/10.1103/PhysRevE.85.046117