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Colloquium Schedule

Spring 2019

Electric Power from Earth's Rotation Through Its Own Magnetic Field

Christopher Chyba ('82), Princeton University
Fri., Mar. 8, 2019, 12:30 PM in Science Center 199

If we rotate a permanent magnet about its north-south axis, does its axially-symmetric magnetic field rotate together with the magnet? What about for an electromagnet? If the axially symmetric field does not rotate with a rotating electromagnet, does this mean that the Earth is rotating through the axially symmetric component of its own internally generated magnetic field? Then what happens? Could the resulting Lorentz force be used to drive electrons around a circuit and generate electricity, powered by the Earth's rotational kinetic energy?

Michael Faraday started asking these questions in 1831. I'll review the developments since then, concluding that the Earth does in fact rotate through the axially symmetric component of its own field. I will then present a simple proof that it is impossible to use this effect to generate electric power. Finally, I will demonstrate, and explore, a loophole in that impossibility proof.

The Cassini Mission to Saturn: An Insider's View of an International Journey of Discovery

Richard French, Wellesley College
Thu., Mar. 28, 2019, 4:30 PM in Science Center 181

The Cassini mission to Saturn transformed our understanding of this beautiful ringed planet and its entourage of moons. Share an insider's view of the mission, from the project's inception to the final months of up-close exploration of this giant world, with the the Cassini Mission Radio Science Team Leader.

Thermal Effects on the Sedimentation of Macroscopic Grains

Ted Brzinski, Haverford College
Fri., Apr. 12, 2019, 12:30 PM in Science Center 199

In 1851 Stokes solved the motion of a single sphere settling in a viscous liquid at low Reynolds’ number.  It took over a 100 years, until 1961, before Brenner determined the behavior of just 2 spheres! in the following 5 decades, the collective motion of dispersions of settling grains has been the subject of active and sustained study. While we have developed empirical models that describe the dynamics of such systems, our understanding of the underlying mechanics have not much improved since Brenner. A recent metanalysis of sedimentation data revealed that the settling speeds can be collapsed onto a master curve with two distinct branches. This bifurcation suggests an exciting new window into the grain-scale interactions that lead to the bulk settling behavior of these systems - a puzzle over 150 years in the making!  I will explain these results in detail, and describe ongoing experiments intended to explore the implications of this new observation.