Probing students' reasoning with multi-variable expressions in the context of potential difference

Safana Ismael

Candidate for Ph.D.
Department of Physics,
North Dakota State University

Monday, Dec. 4, 3:00-4:00pm, 208 South Engineering.

Refreshments at 2:30

Research suggests that some reasoning difficulties persist even after targeted instruction. One such instance is the student’s incorrect reasoning with multi-variable expressions in the context of Electromagnetism in the calculus-based introductory physics course. In this talk, I will focus on student reasoning with Potential Difference, DV=-WEF/qtest. Specifically, after relevant instruction, students struggle to recognize that if the value of a test charge moving between two points is changed, the potential difference between the two points remains the same.  We designed instructional intervention (a blend of web-based assignments and classroom instruction) to prob students' reasoning with multivariable expressions in the context of (1) math problems and (2) analogous problems in the context of physics. The results suggest that student performance on math problems does not predict their performance on analogous problems in the context of physics.

Viscoelasticity and the Persson-Brener Model

Kurt VanDonselaar

Candidate for Ph.D.
Department of Physics,
North Dakota State University

Monday, Oct. 29, 3:00-4:00pm, 208 South Engineering.

Refreshments at 2:30

Polymeric coatings are widely produced by industry and used to create barriers between structures and the elements. Recently, effort has focused on soft coatings that prevent ice and other unwanted foulants from adhering to surfaces. While low surface energies of soft materials, such as polydimethylsiloxanes (PDMS), promise easy removal of attached foulants and ice, the simple physical limit based on surface energy has not been achieved in practice. It is largely believed that the failure is due to viscoelastic losses in the soft coating materials. To better understand the viscoelastic losses in soft adherent PDMS materials, we perform JKR adhesion experiments on several elastomers, at different temperatures and over a set of speeds that spans several orders of magnitude. Each elastomer also undergoes DMA experiments to characterize the dynamic mechanical modulus from the glassy to rubbery regime. We demonstrate that the adhesion tests are qualitatively related to the dynamic moduli and use a more direct comparison (the Persson-Brener model of crack propagation [1]) to show a quantitative relationship between adhesion and dynamic moduli at low speeds.

[1]  B. N. J. Persson and E. A. Brener, “Crack propagation in viscoelastic solids,” PHYSICAL REVIEW E 71, 036123 (2005).

Bio:Kurt VanDonselaar is a Ph.D. student at North Dakota State University. He is studying polymeric materials in the Croll lab. He earned a B.S. in physics from Winona State University and a M.S. in physics from the University of Minnesota Duluth.

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