June 16th, 2021

лошадь, диаграмма, Фейнман

Почему подставки под пиво плохо летают?

Красивая теор.мех.задачка:)

Beer Mats make bad Frisbees: https://arxiv.org/abs/2106.08238
Johann Ostmeyer, Christoph Schürmann, Carsten Urbach
In this article we show why flying and rotating beer mats, CDs, or other flat disks will eventually flip in the air and end up flying with backspin, thus, making them unusable as frisbees. The crucial effect responsible for the flipping is found to be the lift attacking not in the center of mass but slightly offset to the forward edge. This induces a torque leading to a precession towards backspin orientation. An effective theory is developed providing an approximate solution for the disk's trajectory with a minimal set of parameters. Our theoretical results are confronted with experimental results obtained using a beer mat shooting apparatus and a high speed camera. Very good agreement is found.
лошадь, диаграмма, Фейнман

Симпатичное учебное

Раз - задача о брахистохроне:

The Brachistochrone: An excellent problem for all levels of physics students: https://arxiv.org/abs/2106.07726
John A. Milsom
The classic brachistrochrone problem is standard material in intermediate mechanics. Many variations exist including some accessible to introductory students. While a quantitative solution isn't feasible in introductory classes, qualitative discussions can be very beneficial since kinematics, Newton's Laws, energy conservation and motion along curved trajectories all play a role. In this work, we describe an activity focusing on a qualitative understanding of the brachistochrone and examine the performance of freshmen, juniors and graduate students. The activity can be downloaded at this https URL .
Comments: The following article has been accepted by The Physics Teacher

Два - интерферометрия Ханбери Брауна - Твисса для... водопада!

Hanbury Brown and Twiss effect demonstrated for sound waves from a waterfall; an experimental, numerical and analytical study: https://arxiv.org/abs/2106.08137
Arnt Inge Vistnes, Joakim Bergli
The Hanbury Brown and Twiss effect (HBT) is described by numerical and analytical modeling, as well as experimentally, using sound waves and easily available instrumentation. An interesting phenomenon that has often been considered too difficult to be included in standard physics studies at bachelor and master level, can now be introduced even for second year bachelor students and up. In the original Hanbury Brown and Twiss effect the angular size of the source (the star Sirius) was calculated by determining the distance between two detectors that lead to a drop in the cross-correlations in the signals from the detectors. We find that this principle works equally well by sound waves from a waterfall. This is remarkable, since we use a completely different kind of waves from the HBT case, the frequency of the waves differ by a factor ∼1012 and the wavelength as well as the angular extension of the source seen from the observer's position differ by a factor ∼107. The original HBT papers were based on measurements of \emph{intensity} fluctuations recorded by two detectors and correlations between these signals. The starting point for the theory that explained the effect was therefore intensity fluctuations per see, and the theory is not easy to understand, at least not for an undergraduate physics student. Our starting point is descriptions of broadband waves at the amplitude level (not at intensity level) by numerical modeling. Important properties of broadband waves can easily be revealed and understood by numerical modeling, and time-resolved frequency analysis (TFA) based on Morlet wavelets turns out to be a very useful tool. In fact, we think it has been far too little attention to broadband waves in physics education hitherto, but the growth of use of numerical methods in basic physics courses opens up new possibilities.

Ну, и до кучи, скучная педагогика, но для тех, кому предстоит сочинять тесты, может представлять ценность готовыми вопросами:

Investigating Unprompted and Prompted Diagrams Generated by Physics MajorsDuring Problem Solving: https://arxiv.org/abs/2106.07765
Michael Vignal, Bethany R. Wilcox
Diagrams are ubiquitous in physics, especially in physics education and physics problem solving. Problem solvers may generate diagrams to orient to a scenario, to organize information, to directly extract an answer, or as a tool of communication. In this study, we interviewed 19 undergraduate and graduate physics majors, asking them to solve 18 multiple-choice physics problems -- with no prompting regarding diagrams -- and then six diagramming tasks of situations similar to six of the multiple-choice problems. By comparing spontaneously generated and prompted diagrams, we identify different diagramming elements and features used by physics majors acting towards different ends (\textit{i.e.,} in different epistemic frames). We found that different physical contexts impact how critical it is to draw an accurate diagram, and that the differences in diagramming between cohorts (\textit{e.g.}, between lower-division undergraduate and graduate students) seem to be smaller than the differences within a cohort. We also explore implications for teaching and research.
Comments: 16 pages, 11 figures
лошадь, диаграмма, Фейнман

В этот день 1 год назад

Удивительное совпадение - сегодня издательство после двухнедельного молчания ответило на мое напоминающее письмо (оказывается, у них уже отпуска), и оказалось, что новое, третье, толстое издание моей КЭД было отпечатано еще в апреле, просто они забыли выслать мне авторские экземпляры! Но на сайте издательства книжка еще не выложена, потому что - тссссс! - они еще не распродали последние 17 экземпляров прежнего издания:))) Поэтому прошу всех друзей поспособстовать в меру возможностей раскупке этих несчастных 17 книжечек, чтобы новая, толстая и зеленая КЭД воссияла во всей красе! Вот ссылка: https://shop.rcd.ru/catalog/universitetskie-uchebniki-i-uchebnye-posobiya/18703/

Этот пост был опубликован 1 год назад!