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53m
comment Electron velocity in hydrogen
@F.Ha The uncertainty principle is why this doesn't represent an answer to your question (and why there isn't an answer). Neither position nor momentum commute with the Hamiltonian of this system, so neither have a well defined value for states characterized by good quantum number of the system. They only have distributions. But that means that what Veritas proposes represents the expected result for an average over an ensemble of measurements. That's experimentally well defined, but it doesn't tell you anything definite about a single example of the system.
1h
comment What factors will make Earth re-rotate again if it stopped?
Note that as the tidal lock proceeds the Moon moves out and it's tidal strength drops. I don't know if that would effect the eventual balance, but it makes the off-hand observation that the Moon's tidal effect is stronger in this epoch less useful than it seems at first.
12h
comment Electron velocity in hydrogen
You can, but you shouldn't. Or at a minimum you shouldn't do so in the presence of beginners. Because they'll misunderstand what it means every time.
12h
comment Pole and Barn Paradox w/ Spacetime Interval
As usual thinking about 'length contraction' gets confounded because length measurements assume that thing happen simultaneously which they do in only one of a pair of frames in motion relative one another. But given the nature of the title, the point may be to find the result without appealing to the Lorentz transform, which means constructing the space-time diagram (which is, of course, equivalent in information content).
12h
comment Pole and Barn Paradox w/ Spacetime Interval
By the way -\left( \frac{L}{2} \right) will give you $-\left( \frac{L}{2} \right)$ which looks a lot better.
15h
comment Colliding beams vs static target
This problem (and ones similar to it) is given a lot for a reason. I haven't (and won't) check you figures, but this effect occurs in non-relativistic regimes to a degree as well and you may be applying intuition that is based on a Newtonian understanding. Think about what the velocity addition law does for you in this case; or about the difference in speed between the beam and the CoM in the fixed target version of the experiment.
18h
comment The Sun's space-time warp
I suppose that the question is brought on by some pop-sci description of general relativity, but I'm afraid it will not be well received because Physics is not primarily a resources for laymen and we expect questions to be written in a manner consistent with the actual language of the discipline.
18h
comment Question about Bubble chamber reactions
There are some conceptual questions you could ask to illuminate what is going on in here. Things like what the track of a neutral particle looks like, and how one determines the sign of the charge on the particle that made a track and how quickly various particle lose energy in the medium of the chamber.
20h
comment Electric potential inside a solid sphere
Under the current policy this questions is "homework-like" in that it is about the method to solve a particular instance of a problem and not about the underlying concepts. Showing effort is never sufficient to make a question on topic. While there is an on-going effort on meta to build a new, more detailed consensus about what to do with questions of this kind it has not reached a point where it can be applied on the site.
1d
comment The scope of physics, as taught in modern times
On the matter of practical , experimental skills, if you get into a big-science field you will get a lot of help from collaborators in bootstrapping those practical skills. But you still have to build up to having skills to offer that are sufficiently special that you become a valuable contributor who people invite to join; which means going beyond what your peers and mentors can teach you. The whole business is a fertile ground for growing a beautiful case of imposter syndrome.
1d
comment Could I pick up a human with a strong enough magnet?
Have you seen the videos of magnetically levitated frogs? They are worth watching.
1d
comment What is the minimum sample sizes to show the error bar in an experiment?
It's worth noting that if you don't think the error bar means something than you have admitted that you don't know anything about the validity of your data. Arguably you shouldn't be showing that kind of data at all. Also, obligatory comic link: phdcomics.com/comics.php?f=1816
2d
comment Would it be correct to state that all the forms of everyday matter (mountains, tables, buildings, people, etc.) are in a metastable state?
Well, I can't summarize the whole paper but on timescales orders of magnitude longer than the current age of the universe those nuclei are unstable to tunneling fusion. That's what I mean by time-scale mattering.
2d
comment Would it be correct to state that all the forms of everyday matter (mountains, tables, buildings, people, etc.) are in a metastable state?
@lemon Read the Dyson paper for the view over very long time-scales.
2d
comment What are the conditions for the string of a pendulum to become slack?
I don't think that you can properly analyze this problem without taking tensile strain into account which means the possible presence of elastic potential energy in the system as well.
2d
comment Would it be correct to state that all the forms of everyday matter (mountains, tables, buildings, people, etc.) are in a metastable state?
Meta-stability is a matter of time-scale. Sure, you can take the arbitrarily long view and say it, but beware: as a factoid devoid of information about that time scale it is just the kind of "I love science" nonsense that happiness and cyanide spoof as posterior ogling. For a more serious application (though rather dated now), see Dyson's paper "Time Without End" (or in plain text if you can't get past the paywall).
May
2
comment What experimental measurement could be used to show that a neutrino is a Majorana and not a Dirac particle?
It'd be worth noting that there are several neutrinoless double beta decay experiments at the large-prototype to small-full-physics-detevtor scale running now. And so far results have been limited to excluding parts of the phase space. I haven't updated my answer to physics.stackexchange.com/questions/28279/… recently, but there are a few specifics there.
May
2
comment What are the components of r-hat in spherical coordinates?
Your question is equivalent to "What are the Cartesian components of $\hat{x}$?" You've over thinking it.
May
1
comment Breakdown of Snell
"They have their own methods." Do you mean the lens maker's formula? It's based on Snell's Law, Euclidian geometry and an assumption that the lens is thin-compared to its transverse extent. Those lenses are no where near thin enough to worry about surface effects.
May
1
comment How do they know their velocity in a spaceship?
As things stand this remains primarily a pointer to off-site resources, with little of the answer summarized locally.