May 23, 1996
Vol. 15, No. 18

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    Quantrell Award: Sidney Nagel

    Professor in Physics For Sidney Nagel, Professor in Physics, it was a college course on electricity and magnetism that made him want to study physics.

    "The field of electricity and magnetism has the greatest surprises in physics embedded in it," he said. "I love teaching it because I think if people can see how the different pieces of knowledge come together to make something great, it's very satisfying."

    Nagel said that at the end of his class, students have grappled with assignments that deal with the electric and magnetic forces between objects on a tabletop. When the final calculations are done, he said, the students realize that between electricity and magnetism they have found physical laws that imply the existence of light.

    "It's just so absolutely amazing that you can get this other phenomenon, so apparently unrelated," he said. "What I like most about teaching is seeing a student struggle with an idea and then get it, and see the pleasure in the understanding."

    Pleasure finds its way into Nagel's research as well. It's impossible to sit down in his office without picking up a toy. Nagel's large office has two desks, one of which is entirely covered with physics gadgets that range from Slinkys to spinning tops and from iridescent, rheoscopic fluids to liquid crystals that change color with the heat of your hand.

    "Each of these toys demonstrates some important principle of physics, or something related to my research," he said. "Everyone who comes in here has a toy they can't keep their hands off of."

    The Slinky is for studying mechanics and waves; the tops illustrate friction and angular momentum. Rheoscopic fluids, when swirled in a glass jar, form iridescent tendrils of turbulence; liquid crystals show how macroscopic physical properties change when temperature forces the realignment of microscopic molecules.

    Nagel often tackles the complex physics problems embedded in what appear to be fairly ordinary, ubiquitous and well-understood phenomena -- in coffee stains, for example.

    "You can't make coffee without it happening. You drip a bit here, a bit there and you end up with a stain on your desktop, tabletop, tie, whatever." Nagel has glass microscope slides with evaporated coffee drops on them. When held up to the light, they clearly show a dark ring around the edge. The question for Nagel and his collaborators in the Mathematics and Physics departments is, why does all the stuff always go to the edge when it evaporates? "We don't understand this phenomenon," he said, "even though it happens all the time."

    Studying coffee drops is valuable, Nagel said, because this phenomenon occurs not just with coffee, but with any kind of liquid that has solids dissolved in it -- from paint to geologic formations.

    "If we understand the physical mechanisms, then maybe it's something that we can begin to control," he said. The research has important implications for such industries as the paint industry, which delivers its final products through the evaporation of a solvent.

    Nagel's research is concentrated in three major areas: granular materials, liquid-solid phase transitions and hydrodynamics (the behavior of water drops). "In general, it's all about pattern formation," he said.

    But sometimes, physics is just plain fun, and part of the fun is that not everything can be explained. "The problem with having all these toys in here," he said, "is that people ask me how they all work. And I don't know how they all work!"

    Nagel received his B.A. from Columbia in 1969 and his M.A. in 1971 and his Ph.D. in 1974 from Princeton. He joined the Chicago faculty in 1976.

    -- Diana Steele