Studies of collisions in the introductory laboratory often use carts moving on air tracks or along dynamics tracks. As an alternative, students in our laboratories study collisions through experiments that determine coefficients of restitution ε's of balls used in sport. Since ε's are crucial to the outcome of many sporting events, such activities provide students with a “real-world” context for studying collisions. In the process of investigation and analysis, students learn about inelastic collisions, energy transfer, and elasticity of materials.

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For the first time, electron paramagnetic resonance spectroscopy was used to compare numbers and distributions of radicals produced in frontal free‐radical polymerization of multifunctional acrylates and methacrylates to those produced by bulk free‐radical polymerization. A comparison of radical concentrations was performed for individual polymers and selected copolymers of trimethylolpropane trimethacrylate (TMPTMA), 1,6‐hexanediol diacrylate, trimethylolpropane triacrylate, and pentaerythritol tetraacrylate (PETA). Frontally polymerized samples showed a large spike in intensity at the point of initiation. Within a few centimeters, the radical signal diminished to a steady state. The radical concentration remained almost constant over 3 months under helium in flame‐sealed tubes. The types of radicals were similar to those in bulk polymerization. For both TMPTMA and PETA, frontally polymerized samples had significantly higher numbers of radicals than did the bulk‐prepared samples, achieving concentrations as high as 8.7 × 10−3 mol/kg in the frontally prepared samples of TMPTMA. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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A simple, highly effective demonstration of mutual repulsion (attraction) between parallel conductors is described for the classroom. The physical effects are clearly elucidated using readily available materials in conjunction with a high-current (20 A) dc power supply.