Description:

“Mind the gap: a new kind of fingering instability in colloidal rollers”
Dr. Michelle Driscoll, Northwestern University-Department of Physics and Astronomy

When colloidal particles are rotated adjacent to nearby floor, strong advective flows are generated around them, even quite far away. When a group of these microrollers is driven, the strong hydrodynamic coupling between particles leads to formation of new structures: an initially uniform front of microrollers evolves first into a shock-like structure, which then quickly becomes unstable, emitting fingers of a well-defined wavelength. Our experiments and simulations confirm that this instability is quite different than typical fingering instabilities, where size scale selection is a consequence of competing stresses. Here, this instability arises only due to hydrodynamic interactions, and it is controlled by a single geometric parameter, the particle-floor height. Our measurements of the growth rate in both experiments and simulations agree with results from our continuum model. This instability is a direct consequence of the inward flows created by the interactions between the particles and the nearby solid surface.

“Classical physics and personal experience: Two contemplative practices”
Dr. Zosia Krusberg, Northwestern University-Department of Physics and Astronomy

One of the primary objectives of the introductory physics curriculum is for students to become aware of the connections between the fundamental principles of classical physics and their personal experience. However, numerous studies have shown that students’ awareness of such connections tends to deteriorate, sometimes substantially, following instruction. In this work, we present two contemplative practices aimed at deepening students’ experiential engagement with the connection between physics concepts and the physical world, in the first practice, by heightening their awareness of their sensory experiences and, in the second practice, by continually directing their attention to visual manifestations of physical principles in nature and in the public and private spaces they inhabit. Additionally, we discuss the written assessments of these practices, and find that – in line with the central objectives of the study – students expressed a heightened awareness of their physical embodiment and the richness of their sensory experience, the applicability of physics concepts to their personal experience, and the natural emergence of questions in response to observations of the physical world. Students also reported general enjoyment, excitement, and/or gratitude about the practice, deepened relaxation and mental clarity, as well as a heightened metacognitive and meta-affective awareness.