What type of forces and motions can be generated by the chemical potential? We address this question through a set of environmentally relevant phenomena in which the chemical potential plays a crucial role. These phenomena include atmospheric pressure, osmotic energy production, and the nucleation of cloud drops, which also illustrate the relationship between the chemical potential and Newtonian forces.

Understanding the magnetic properties of matter plays a key role in materials physics. However, university education on fundamental magnetism is often limited to a theoretical survey because of the lack of appropriate apparatus that can be applied for laboratory courses at the undergraduate level. In this work, we introduce an AC magnetometer based on the Colpitts self-oscillator with an inductor coil as a probe. We show that this type of self-oscillator can be adopted in a typical university laboratory course to learn the principles of magnetic measurement and to understand the fundamental magnetism of matter. We demonstrate the exceptional stability of the circuit with a working frequency range of 10 kHz–10 MHz and excellent performance to detect a diamagnetic signal from a superconductor at cryogenic temperatures.

This paper presents a compact, low-cost optical setup designed for measuring refractive indices of liquid samples. The system employs a tilted transparent quartz cuvette placed on a rotating stage, where a small angular offset between the laser beam and the cuvette induces a lateral displacement of the transmitted beam. By quantifying this displacement, the refractive index of liquids (water and 1-propanol in this paper) is determined with minimal optical complexity. The laser beam displacement is accurately quantified by the knife-edge technique. Key physical quantities, including beam displacement and refractive index, are derived through an optical ray transfer matrix. Students typically obtain accuracy of three significant figures after the decimal point. Experimental results demonstrate agreement with theoretical models, validating the method's precision for applications in materials science, biochemical sensing, or quality control. Considering the simplicity, affordability, and versatility of this device, the setup integrates practical optical experiments with fundamental optical principles, making it well-suited for both research and educational environments.

The spreading of a thin viscous fluid film on a horizontal surface is an interesting problem in fluid mechanics with many practical applications ranging from coating processes to biological systems and environmental flows. It can even be observed in everyday situations, such as syrup spreading on a pancake. We present a project-based learning approach to this problem, in which engineering or physics undergraduates apply classroom knowledge to understand and solve it, using dimensional analysis, experiments, and theoretical modeling. First, a dimensional analysis is conducted to guide the design of the experiment suitable for an undergraduate laboratory or even at home. The problem is then simplified to obtain a mathematical model that accounts for the experimental results. Through this process, students are able to obtain a solution compatible with those published in fluid mechanics journals with minimal supervision from the instructor. This project not only develops important skills but also motivates students by showing that they have the ability to solve complex problems.

The common New England sight of a cranberry bog presents a rich tapestry of fluid dynamics and soft matter phenomena. Here, we present four connected problems exploring the behavior of cranberries in their stages of harvest: the buoyant rise of a cranberry in a flooded bog, the stable floating configuration of a cranberry on the surface, the aggregation and interaction between many floating cranberries collected with a boom, and the piling of cranberries onto a truck for transportation. We model these phenomena from first principles and develop simple computational simulations of their collective behaviors. Additionally, we describe tabletop experiments to accompany these problems, either as in-class demonstrations or lab activities. Throughout, we draw connections to broader physical principles in soft condensed matter and fluids, allowing the real-world example of the cranberry bog to serve as a bridge between the undergraduate curriculum and topics in soft matter research.

The Wigner's friend paradox, like the Schrödinger's cat paradox, challenges our understanding of the foundations of quantum theory. The paradox is best illustrated by a brief scenario featuring two observers who draw different conclusions. We describe the Wigner's friend scenario as told by E. P. Wigner, and then an earlier version as told by Hugh Everett. Wigner and Everett offer different resolutions of essentially the same paradox. Decoherence theory provides a third resolution. Despite different interpretations (or their absence), these three stories fit together to form a consistent picture without a paradox.

The spherical cow approximation is widely used in the literature but is rarely justified. Here, I propose several schemes for extending the spherical cow approximation to a full multipole expansion, in which the spherical cow is simply the first term. This allows for the computation of bovine potentials and interactions beyond spherical symmetry and also provides a scheme for defining the geometry of the cow itself at higher multipole moments. This is especially important for the treatment of physical processes that are suppressed by spherical symmetry, such as the spindown of a rotating cow due to the emission of gravitational waves. I demonstrate the computation of multipole coefficients for a benchmark cow and illustrate the applicability of the multipolar cow to several important problems.

Optical coherence tomography (OCT) has become increasingly important in fundamental research, medical diagnostics, material characterization, and industrial process monitoring. OCT measures the depth-dependent reflectivity of a sample with micrometer-scale resolution by analyzing the interference between light reflected from the sample and a reference arm. Despite its widespread application, OCT remains underrepresented in undergraduate curricula due to the complexity and cost of commercial systems. Our contribution presents educational implementations of the two most widely used OCT modalities: swept-source OCT and spectral-domain OCT. In our swept-source setup, a grating monochromator is used as a tunable light source, providing a clear and cost-effective realization of wavelength sweeping. For our spectral-domain setup, we developed a compact, self-built two-dimensional spectrometer enabling efficient spectral acquisition. Both systems are capable of producing three-dimensional representations of the internal sample structure. Designed with open architecture and minimal complexity, these setups prioritize visibility of core principles, making them well-suited for hands-on learning in undergraduate laboratory environments.