ISSN:0002-9505    

DOI:10.1119/5.0075152

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP

摘要:

This Resource Letter provides an overview of the literature in biological physics, a vast, active, and expanding field that links the phenomena of the living world to the tools and perspectives of physics. While no survey of this area could be complete, this list and commentary are intended to help provide an entry point for upper-level undergraduates, graduate students, researchers new to biophysics, or workers in subfields of biophysics who wish to expand their horizons. Topics covered include subcellular structure and function, cell-scale mechanics and organization, collective behaviors and embryogenesis, genetic networks, and ecological dynamics.

ISSN:0002-9505    

DOI:10.1119/5.0060279

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP

摘要:

Non-Euclidean geometry can be taught to students using astronomical images. By using photographs of the Moon taken with a smartphone through a simple telescope, we were able to introduce these concepts to high-school students and lower-level college students. We teach students how to calculate lengths of mountain ranges or areas of craters on the Moon's surface and introduce ideas of geodesics and spherical triangles. Students can see that accurate measurements cannot be obtained using flat geometry. Instead, by using three-dimensional curved geometry, estimates of lengths and areas can be computed with less than 4% error.

ISSN:0002-9505    

DOI:10.1119/10.0006156

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP

摘要:

10.1119/10.0005989.1The electrical power grid has been described as the largest machine in the world. Although we customarily assume our electrical outlets provide a steady sinusoidal voltage with a frequency of 60 Hz (in North America), the variations from that ideal are easy to observe using the methods described in this article. These frequency variations are important since, as can be shown with introductory-level physics concepts, they arise when power generation and usage are not balanced on the electrical grid. The challenge of balancing the electrical grid will increase over the coming years as we adopt more sustainable but less predictable energy sources, and this connection to one of our current societal challenges makes this project interesting to students.

ISSN:0002-9505    

DOI:10.1119/10.0005989

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP

摘要:

A new perspective on the ubiquity of classical harmonic oscillators is presented based on the two-variable Taylor expansion of a perturbed system's total energyE(q,q̇), whereq(t) is the system displacement as a function of timetandq̇(t)=dq/dt. This generalised approach permits derivation of the lossless oscillator equation from energy arguments only, yielding a universal equation for the oscillation frequencyω=(∂2E/∂q2)/(∂2E/∂q̇2)which may be applied to arbitrary systems without the need to form system-specific linearised models. As illustrated by a range of examples, this perspective gives a unifying explanation for the prevalence of harmonic oscillators in classical physics, can be extended to include damping effects and driving forces, and is a powerful tool for simplifying the analyses of perturbed systems.

ISSN:0002-9505    

DOI:10.1119/10.0005948

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP

摘要:

We revisit the classical mechanics problem of a particle moving under the influence of a force that depends on its velocity. Using the properties of the rotation matrix and associated operators, we show that it is possible to find an exact analytical solution to a number of problems where the differential equation of motion depends on the velocity. First, we apply our method to the well-known cases of a particle under the influence of the Lorentz force and Coriolis force, providing the complete analytical solution in each case for the motion of the particle in three dimensions. We also show that the complete solution can be obtained when the centrifugal force is included, showing the applicability to cases where there is simultaneous dependence on the position and velocity. This method, which is not currently discussed in a typical course in elementary mechanics, provides an alternative approach to the traditional methods that are used to solve these types of problems.

ISSN:0002-9505    

DOI:10.1119/10.0005992

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP

摘要:

The classical and quantum description of a free particle moving inside a confocal parabolic billiard is studied. From a classical approach, we derive the characteristic equations for periodic trajectories, discuss the Poincaré maps, and explore interesting geometrical properties of the orbits inside the billiard. From a quantum description, we determine the eigenstates and energy spectrum of the confined particle. The confocal parabolic billiard is an integrable system that exhibits two degrees of freedom and two constants of motion. The way to establish a correspondence between the classical and quantum solutions is by equating the constants of motion for both descriptions. The parabolic billiard provides a well-motivated and relatively straightforward example of the Hamilton–Jacobi theory in a way that is seldom discussed in the undergraduate curriculum.

ISSN:0002-9505    

DOI:10.1119/10.0006018

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP

摘要:

The Szilárd engine is a mechanism (akin to Maxwell's demon) for converting information into energy, which seemingly violates the second law of thermodynamics. Originally a classical thought experiment, it was extended to a quantized treatment by Zurek. Here, we examine a new, elegant model of a quantum Szilárd engine by replacing the traditional rigid box with a harmonic potential, extending the scope of the model. Remarkably, almost all calculations are exact. This article is suitable for students, researchers, and educators interested in the conceptual links among information, entropy, and quantum measurement.

ISSN:0002-9505    

DOI:10.1119/10.0005946

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP

摘要:

Even 100 years after its introduction by Louis de Broglie, the wave-nature of matter is often regarded as a mind-boggling phenomenon. To give an intuitive introduction to this field, we here discuss the diffraction of massive molecules through a single, a double, and a triple slit, as well as a nanomechanical grating. While the experiments are in good agreement with undergraduate textbook predictions, we also observe pronounced differences resulting from the molecules' mass and internal complexity. The molecules' polarizability causes an attractive van der Waals interaction with the slit walls, which can be modified by rotating the nanomechanical mask with respect to the molecular beam. The text is meant to introduce students and teachers to the concepts of molecule diffraction, supported by problems and solutions that can be discussed in class.

ISSN:0002-9505    

DOI:10.1119/5.0058805

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP

摘要:

In this work, we present (and encourage the use of) the Williamson theorem and its consequences in several contexts in physics. We demonstrate this theorem using only basic concepts of linear algebra and symplectic matrices. As an immediate application in the context of small oscillations, we show that applying this theorem reveals the normal-mode coordinates and frequencies of the system in the Hamiltonian scenario. A modest introduction of the symplectic formalism in quantum mechanics is presented, using the theorem to study quantum normal modes and canonical distributions of thermodynamically stable systems described by quadratic Hamiltonians. As a last example, a more advanced topic concerning uncertainty relations is developed to show once more its utility in a distinct and modern perspective.

ISSN:0002-9505    

DOI:10.1119/10.0005944

出版商:American Association of Physics Teachers    

年代:2021

数据来源: AIP