# Tag Info

3

You talk about time, but usually when I think "physical constant" I think of something more like $c$ or $\hbar$. Since we're increasingly using those kinds of constants to construct our units, it's a bit difficult to say how well they're measured--$c$ isn't measured, it's defined, for instance. For that reason, I think we ought to pick a dimensionless ...

8

I'll give it a try: Jesse L. Silverberg, Matthew Bierbaum, James P. Sethna, and Itai Cohen, Phys. Rev. Lett. 110, 228701 (2013): "Collective Motion of Humans in Mosh and Circle Pits at Heavy Metal Concerts". (I got the idea from a Sixty Symbols video.) http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.228701 It's not written by someone famous ...

3

I'm going to be perverse and suggest Blas Cabrera's "First Results from a Superconductive Detector for Moving Magnetic Monopoles" (Phys. Rev. Lett. 48, 1378 (1982).) Cabrera isn't a household name, of course, but this does have some advantages as a teaching paper: First, the experiment is dead simple to explain to students who know about EMFs and ...

0

From the details I assume it needs to concern a specific experiment, rather than just some musings. In recent news, in Nature Chemestry, "Coulomb explosion during the early stages of the reaction of alkali metals with water" (online version) has the Mythbusters appeal. When combined with the you-tube lead-up to the formal experiments, it is quite ...

4

As noted in P. Weinberger's revisit of Louis de Broglie's 1924 doctoral thesis: De Broglie's contribution in the Philosophical Magazine from 1924 is fascinating from many standpoints: for its moderate use of mathematics, the close connection to Einstein's special theory of relativity, and of course for the proposal of matter waves. We revisit ...

11

It seems to me Fermi's 1949 paper On the origin of the cosmic radiation (pdf copy link) is fairly accessible, requiring basic E&M and conservation of energy & momentum. The paper was written as a proposal for a mechanism to accelerate cosmic rays from thermal velocities to relativistic ones. The mechanism he proposes (based on Alfven waves) ...

35

If you want research-level physics papers about topics high school students can understand, your best bet might be to look to the past. Older papers are great fun to read, but with their archaic language and notation they're not always the most efficient way to learn. One famous exception is Einstein's 1905 classic On the Electrodynamics of Moving Bodies. ...

1

Mathematically speaking they are the same operator. Usually we reserve the d'Alembertian for 3+1 dimensional spacetime (so in absence of curvature it takes the form $\partial_0^2 - \nabla^2$), while the Laplace-Beltrami operator is defined for an aribtrary dimensional manifold with arbitrary signature. The only possible difference is that sometimes (not ...

1

In nuclear physics, an exited atom is exited due to its nuclei spins being aligned in a energetically not minimized constellation. This can happen due to external energy intake or as a part of a radioactive decay where the mother nucleus' spin constellation is carried over but then nearly instantaneous changes in its daugther nucleus. The freed energy of the ...

4

First let me repeat what Yvan Velenik says in the comment: The terminology is somewhat unfortunate, because you don't need that much statistics, rather you'll need some probability theory. To elaborate, quoting Wikipedia, Statistics is the study of the collection, analysis, interpretation, presentation, and organization of data. [...] Statistics deals ...

2

The notation is that of one specific isotope (isotopes are nuclides with the same number of protons) of the chemical element Pu. 94 is the number of its protons, which is also the total charge, 240 is the total number of nucleons (protons and neutrons). In a neutral Pu atom there will always be 94 electrons to offset the charge of the protons in the nucleus. ...

5

Either. It's context dependent. Chemists generally mean the whole atoms, nuclear physicists usually mean the nucleus, and people not in those categories could mean either. And there are exception to all those rules or thumb. And the distinctions is important when people start throwing masses around because the mass of an electron is almost on the same ...

1

The entire atom is referred to by Pu.

4

In general, energy levels apply to the system1 (in your case the system of electron(s) and nucleus is the atom). So it is entirely appropriate to say that the atom is excited. It is only a few cases where it makes sense to factor the notion out and say that "this piece of the system" is excited. That works OK with hydrogen-like atoms because the nucleus is ...

2

People who work with neutrons frequently find themselves discussing mega-electronvolts (MeV, typical nuclear energy) and milli-electronvolts (meV, typical room-temperature thermal energy) in the same sentence. It is mostly not a problem to use MeV and meV when writing. When speaking, some people will say "big em ee vee" or "little em ee vee", or pronounce ...

5

Two conventions. First - use a capital M - make sure you make it big and pointy, so it cannot be confused with lower case: When it is right next to the lower case 'm', the difference should stand out clearly. Second - some people use the "computer short hand" E6: 1.7E6 m This is generally understood to mean (but quicker to write than) $1.7\cdot ... 1 Pretty often I notice that a small rain system or even a large one will congregate or follow a large interstate highway It is like urban pollution. A storm releases rain over cities: City pollution may also impact cloud formation and rainfall. “Water vapor doesn’t ordinarily spontaneously condense into drops to form clouds,” says climate scientist ... 0 Due to the rotation of the Earth, "inner-Earth-dwellers" would feel a fictitious centrifugal force pointing away from the axis of rotation. Ask your students how strong that force would appear to be. Once they realize it's a very weak force indeed, ask them to determine how fast the Earth would be spinning to give inner-Earth-dwellers the appearance of ... 0 For start of conversation, there are infinite quantity of process (functions) of physics that are not computable. The match of a physical process and computability lies in the degree of precision for measurements. The scale of measure defines a basis for computable numbers. e.g. $$\alpha^{-1} \cong 137.035\,999\,173(35)$$$\$\pi \cong ...

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