Session V5: Physics for Everyone

Biomagnetism and Magnetotaxis in Bacteria: What Bacteria Know About Magnetic Materials and Permanent Magnet Design

Magnetotactic bacteria (mtb) migrate along geomagnetic field lines, i.e., they behave like self-propelled magnetic compass needles. Mtb make single-magnetic-domain crystals of magnetite (Fe$_{3}$O$_{4})$ and greigite (Fe$_{3}$S$_{4})$ in intracellular structures called magnetosomes. The magnetosomes are arranged in linear chains that comprise permanent magnetic dipoles with remanent moments approaching the saturation moment, causing the mtb to be oriented in the geomagnetic field as they swim. This allows them to keep their heading and efficiently migrate to, and remain in, a preferred, microaerobic, aquatic habitat. The mtb have solved the difficult problem of designing a permanent magnet that is sufficiently robust to cause the cell to be oriented in the geomagnetic field at ambient temperature, yet fit inside a micron-sized object, and be assembled \textit{in situ} from potentially toxic materials scavenged from the environment. I will describe some recent advances in mtb genetics that illuminate the process by which they make and arrange their magnetosomes.   

Voodoo Science

A remarkable scientific result that appears to violate natural law may portend a revolutionary advance in human knowledge. It is, however, more likely an experimental screw up. Error is normal; it can be reduced by repeating measurements and better design of controls, but the success and credibility of science is anchored in a culture of openness. Ideas and observations are freely exposed to independent testing and evaluation by others. What emerges is the book of nature. On its pages we find, if not a simple world, at least an orderly world, in which everything from the birth of stars to falling in love is governed by the same natural laws. These laws cannot be circumvented by any amount of piety or cleverness, they can be understood - with the possible exception of String Theory. For those who elect to work outside the scientific community, errors may go unrecognized. We will examine examples of this, including claims of perpetual motion and cancer caused by cell-phone radiation.   

M&Ms Packing and Research with Undergrads

This abstract not available.   

Science and Cooking: Motivating the Study of Freshman Physics

This talk will describe a course offered to Harvard undergraduates as a general education science course, meant to intrduce freshman-level science for non-science majors. The course was a collaboration between world-class chefs and science professors. The chefs introduced concepts of cooking and the professors used these to motivate scientific concepts. The lectures were designed to provide a coherent introduction to freshman physics, primarily through soft matter science. The lectures were supplemented by a lab experiments, designed by a team of very talented graduate students and post docs, that supplemented the science taught in lecture. The course was very successful in motivating non-science students to learn, and even enjoy, basic science concepts.   

Making a frothy shampoo or beer

The terms ``foam'' and ``froth'' refer to a dispersion of gas bubbles in a liquid. Why do certain liquids show a tendency to foam while others do not? For example, bubbles can be produced in pure water by vigorous agitation, but then they rapidly coalesce and disappear. While foams cannot be produced with pure water, foams associated with beer or shampoo can persist for several minutes or even hours. What ingredient(s) in shampoo and beer make their foams stable, and what physical concepts control their stability? In this talk I'll review three basic mechanisms underlying foam stability, and I'll make connection with current research on coarsening by the diffusion of gas from smaller to larger bubbles.