Physicists Dive into Oscillation Frequency of Coffee

Scientists puzzle out when and why coffee spills

At a recent math conference, RouslanKrechetnikov watched his colleagues gingerly carry cups of coffee. Why, he wondered, did the coffee sometimes spill and sometimes not? A research project was born.

Although the problem of why coffee spills might seem trivial, it actually brings together a variety of fundamental scientific issues. These include fluid mechanics, the stability of fluid surfaces, interactions between fluids and structures, and the complex biology of walking, explains Krechetnikov, a fluid dynamicist at the University of California, Santa Barbara.

In experiments, he and a graduate student monitored high-speed video of the complex motions of coffee-filled cups people carried, investigating the effects of walking speed and variability among those individuals. Using a frame-by-frame analysis, the researchers found that after people reached their desired walking speed, motions of the cup consisted of large, regular oscillations caused by walking, as well as smaller, irregular and more frequent motions caused by fluctuations from stride to stride, and environmental factors such as uneven floors and distractions.

Coffee spilling depends in large part on the natural oscillation frequency of the beverage—that is, the rate at which it prefers to oscillate, much as every pendulum swings at a precise frequency given its length and the gravitational pull it experiences. When the frequency of the large, regular motions that a cuppa joe experiences is comparable to this natural oscillation frequency, a state of resonance develops: the oscillations reinforce one another, much as pushing on a playground swing at the right point makes it go higher and higher, and the chances of coffee sloshing its way over the edge rise. The small, irregular movements a cup sees can also amplify liquid motion and thus spilling. These findings were to be detailed at a November meeting of the American Physical Society in Baltimore.

Once the key relations between coffee motion and human behavior are understood, it might be possible to develop strategies to control spilling, “such as using a flexible container to act as a sloshing absorber,” Krechetnikov says. A series of rings arranged up and down the inner wall of a container might also impede the liquid oscillations.

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Electron-Atom Collisions

Ian E. McCarthy The Flinders University of South Australia

Eric WeigoldAustralian National University

The detailed study of the motion of electrons in the field of a nucleus has been made possible by quite recent developments in experimental and calculational techniques. Historically it is one of the newest of sciences. Yet conceptually and logically it is very close to the earliest beginnings of physics. Its fascination lies in the fact that it its possible to probe deeper into the dynamics of this system that of any other because there are no serious difficulties in the observation of sufficiently-resolved quantum states or in the understanding of the elementary two-body interaction.

The utility of the study is two-fold. First the understanding of the collisions of electrons with single-nucleus electronic systems is essential to understanding of many astrophysical and terrestrial systems, among the latter being the upper atmosphere, lasers and plasmas. Perhaps more important is its use for developing and sharpening experimental and calculational techniques which do not require much further development for the study of the electronic properties of multinucleus systems in the fields of molecular chemistry and biology and of condensed-matter physics.

For many years after Galileo’s discovery of the basic kinematic law of conservation of momentum, and his understanding of the interconversion of kinetic and potential energy in some terrestrial systems, there was only one system in which the dynamic details were understood. This was the gravitational two-body system, whose understanding depended on Newton’s discovery of the 1/r law governing the potential energy. By understanding the dynamics we mean keeping track of all relevant energy and momentum changes in the system and being able to predict them accurately.

For the next 250 years Newton’s dynamics of force was applied with incomplete success to many incompletely-observed systems. At the same time an understanding of the relationship of momentum, energy, space and time was developed by Maupertius, Euler and Lagrange. The understanding of process involving the production and absorption of bosons began with Maxwell’s equations, although their significance in this sense was not realized until Einstein’s development of the photon concept. Atomic and nuclear physics were born at the same instant, the discovery of the nucleus by Rutherford (1911).

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https://www.sciencedaily.com/releases/2012/02/120209135846.htm