dmckee
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 6h comment Calculate responsivity of a pyroelectric detector I had a grad school professor who occasionally gave us old theory papers and asked us to reproduce part of the argument therein, either in total or for a special case. One time he slipped us a ringer: a paper in a prestigious journal with a simple sign error. Just because it's published doesn't mean it's right. 16h comment What do different frequencies in astrophysics data file mean? On the question of topicality of questions about file formats: we have at least one meta post that relates and there have been question closed and some that survived. 18h comment Quick question on rotational motion It is typical in a first course to expect you to use an inertial frame of reference for all you problems. Worked in that way the is only one horizontal force (the friction with the truck), but the box should have an acceleration toward the center of $v^2/r$. It is equivalent to work in the non-inertial frame of the truck in which the box is in equilibrium but there is the addition of the centrifugal pseudo-force $mv^2/r$ toward the outside, but as I said your instructor might forbid using the non-inertial frame. In any case it is very important that you understand the difference. 19h revised What particles travel near the speed of a photon? added 1 character in body 22h answered What particles travel near the speed of a photon? 1d comment Atomic bomb explosion Related (maybe duplicate): either physics.stackexchange.com/q/233798 or physics.stackexchange.com/q/16974. 1d 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. 1d answered What does “transfer” of angular momentum mean? 1d 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. 1d revised Is the visible light from “red-hot glass” at least close to Blackbody Radiation? Wordo fix for the title 1d 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. 1d 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). 1d 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. 1d 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. 1d 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. 1d 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. 2d 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. 2d 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. May 3 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. May 3 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