November 15th, 2019

лошадь, диаграмма, Фейнман

Готовимся к сезону катков и коньков :)

The pressure underneath a skate at rest:

The pressure distribution is calculated underneath a skate which is pushed in the ice by the weight of a skater at rest. Due to the sharp edges of the skate the deformation is partly elastic and partly plastic. The ratio of the plastic and elastic contribution to the reaction force is determined. Using this ratio the deformation in ice with a finite hardness can be mapped on the problem of the deformation in a purely elastic medium with infinite hardness. Both the upright skate and the tilted position are exactly calculated.
Comments: 20 pages, 5 figures
лошадь, диаграмма, Фейнман

Об одной из фейнмановских задачек

Как раз недавно на нее набрел:) Там она без решения, на "подумать самостоятельно", с предупреждением, что решение не простое:))

A Quantitative Version of Feynman's Static Field Momentum Example:

The Feynman demonstration that electromagnetic field momentum is real, even for static fields, can be made more useful by simplifying its geometry. Instead of Feynman's disk with charged balls on its surface, use a hollow non-conducting sphere with uniform surface charge density. The initial field angular momentum and the final mechanical angular momentum can then be calculated in closed form and shown to be equal. The methods used in the calculation are those available to the average upper-division physics student.
This simplified geometry also provides a test for the current idea that electromagnetic field energy can be considered a form of inertial mass. The mass motion in the simplified Feynman example can be modeled as the static, circular, incompressible flow of a fluid, with distributed nonzero vorticity. But such motion requires a centripetal force or pressure that has yet to be identified.
лошадь, диаграмма, Фейнман

Историко-философское о Стандартной модели

Полезно, по крайней мере, хронологией и обильными ссылками.

The Once and Present Standard Model of Elementary Particle Physics:

There are many theories that have resided these last fifty years within the hazy mist we have been calling the Standard Model (SM) of elementary particles. An attempt is made here to construct a coherent description of the SM today, because only precisely articulated theories can be targeted for annihilation, corroboration, and alteration. To this end it is useful to categorize the facts, mysteries and myths that together build a single conception of the SM. For example, it is argued that constructing a myth for how neutrinos obtain mass is useful for progress. We also advocate for interpreting the cosmological constant, dark matter, baryogenesis, and inflation as four "mysteries of the cosmos" that are indeterminate regarding new particles or interactions, despite a multitude of available particle explanations. Some history of the ever-changing SM is also presented to remind us that today's SM is not our parents' SM, nor will it likely be our children's SM.