A Progression of Static Equilibrium Laboratory Exercises

Although simple architectural structures like bridges, catwalks, cantilevers, and Stonehenge have been integral in human societies for millennia, as have levers and other simple tools, modern students of introductory physics continue to grapple with Newton\u27s conditions for static equilibrium. As formulated in typical introductory physics textbooks, 1–4 these two conditions appear as ΣF=0 (1) and Στ=0, (2) where each torque τ is defined as the cross product between the lever arm vector r and the corresponding applied force F, τ=r×F, (3) having magnitude, τ=Frsinθ. (4) The angle θ here is between the two vectors F and r. In Eq. (1) , upward (downward) forces are considered positive (negative). In Eq. (2) , counterclockwise (clockwise) torques are considered positive (negative). Equation (1) holds that the vector sum of the external forces acting on an object must be zero to prevent linear accelerations; Eq. (2) states that the vector sum of torques due to external forces about any axis must be zero to prevent angular accelerations. In our view these conditions can be problematic for students because a) the equations contain the unfamiliar summation notation Σ, b) students are uncertain of the role of torques in causing rotations, and c) it is not clear why the sum of torques is zero regardless of the choice of axis. Gianino 5 describes an experiment using MBL and a force sensor to convey the meaning of torque as applied to a rigid-body lever system without exploring quantitative aspects of the conditions for static equilibrium

Core Relaxation Effects in Inner Shell Photoionization of Atoms

Inner-shell photoionization of closed-shell systems can be described by modifications of the relativistic random-phase approximation which include relaxation effects. The inclusion of overlap integrals between orbitals of the ground state and the relaxed final state is essential. Methods are reviewed and the results of cross section and matrix element calculations on deep inner subshells are compared with experiment for several atomic systems. In some instances, polarization effects can also play a role. A technique for approximating the effects of polarization is reviewed and its application to the negative iodide ion is presented. © 2003 Published by Elsevier Ltd

The Laser Level as an Optics Laboratory Tool

For decades now, the laser has been used as a handy device for performing ray traces in geometrical optics demonstrations and laboratories. 1 , 2 For many ray- trace applications, I have found the laser level 3 to be even more visually compelling and easy for student use than the laser pointer

An Inexpensive LED Light Sensor

Light irradiance measurements are important for students grappling with abstract optical phenomena such as the inverse square law,1 polarization, diffraction, interference, and spectroscopy. A variety of commercial light sensors are available from scientific vendors such as the CI-6504A from PASCO scientific2 and the LS-BTA from Vernier Software and Technology.3 These sensors, in combination with data acquisition interfaces, allow students to digitally record relative irradiances. Many experiments in elementary lab situations, however, do not require this level of sophistication, and a simple LED connected to a voltmeter performs admirably as a readily available and inexpensive photosensor. LEDs are frequently used in the laboratory as light sources,4,5 but their use as photodetectors6,7 is relatively unknown in the physics teaching community. Here we introduce a few of the basic laboratory applications of common LEDs as photosensors

P-35 A Diffusion Activity for Students

Diffusion is a truly interdisciplinary topic bridging all areas of STEM. Through statistical notions of the random walk, physics brings a unique, stochastic perspective to diffusive processes as first shown by Einstein\u27s Nobel-Prize-winning work on Brownian motion. We present a hands-on educational activity for introductory physics students illustrating diffusion as a random walk. The random-walk activity, data collection and analysis techniques will be presented. Pre- and Post-testing demonstrates that the activity and analysis improves student understanding of the mechanisms underlying diffusion

A Student Diffusion Activity

Diffusion is a truly interdisciplinary topic bridging all areas of STEM education. When biomolecules are not being moved through the body by fluid flow through the circulatory system or by molecular motors, diffusion is the primary mode of transport over short distances. The direction of the diffusive flow of particles is from high concentration toward low concentration

Effects of Relaxation and Interchannel Coupling in Inner-Shell Photoionization of Atomic Ytterbium

Photoionization cross sections, branching ratios, and photoelectron angular-distribution asymmetry parameters have been calculated for the Yb (Z=70) 4f, 4d, and 6s subshells using the relativistic random-phase approximation, the truncated relativistic random-phase approximation, and the relativistic random-phase approximation, modified to include relaxation effects. Comparisons are made between the various approximations and experimental data. Important relaxation effects for the 4f and 4d channels are noted and strong effects of interchannel coupling are noted for 6s photoionization in the region near the 4f and 5p thresholds. © 1994 The American Physical Society

Small Group Learning in the Physics Department of Andrews University

Research has shown that peer instruction in small groups can be a very effective method for students to learn deeply, develop critical thinking skills, and enhance abilities to work as team members. We have instituted a weekly small group activity into the curriculum of the General Physics courses, PHYS141 and PHYS142. The peer instruction is conducted by student Learning Assistants and the material is often interdisciplinary. We will review the literature on small group effectiveness and discuss implementation and outcomes for General Physics