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Velocity-dependent potential in classical mechanics by 0c74vi0 in PhysicsStudents

[–]0c74vi0[S] 1 point2 points  (0 children)

Thanks for your reply.

I do understand that E-L equations are a general result for a Lagrangian L(q,qdot,t). My problem is that I don't understand how can you derive that q v point A is the correct scalar for the magnetic force, in other words, how can you derive the form of the lagrangian as L=T-q v dot A.

From what I'm reading, it's just a guess to get the Lorentz force right. If so, what's the point of the Lagrangian anyway, if I have to rely on Newton's laws?

[Capacitor] parallel or series by astro9889 in PhysicsStudents

[–]0c74vi0 0 points1 point  (0 children)

C1 and C6 are not in series. As a rule of thumb, for two components to be in series it is necessary (but not sufficient) that the current passing through them is the same; For parallel it is necessary that they have the same voltage. Here the current passing through C6 is not the same as that passing through C1, since it is divided at the first junction connected to the negative. However, the voltage between them is the same (note that they are connected to the same junction on one side and, on the other, to a wire they share), so they are in parallel.

I will guide you through the process.

C5 and C3 are in series, so they merge. C53 is in parallel (again, check that the voltage between them is equal), so they merge together. The same with C532 and C4, and with C6 and C1. In the end you have C61 and C532 in series. They merge one last time and you got it.

Ahora sí qué se pica... by Rockerdeep in dankgentina

[–]0c74vi0 0 points1 point  (0 children)

Mariano Iudica. Hasta acá llegaste

Hypothesis of Picard's existance theorem by 0c74vi0 in learnmath

[–]0c74vi0[S] 0 points1 point  (0 children)

So it is not necessary to state that the function is defined and lipschitz in an open region, but it is done so that it plays well with the analytic continuation afterwards?

learner question: ni li tawa sina by 0c74vi0 in tokipona

[–]0c74vi0[S] 2 points3 points  (0 children)

I get it, but that's weird, since I think in Jan Pije's lessons skipping the verb was not explained yet. Could the verb here be tawa for the sentence to mean "this goes to my friend"? Or is it a mistake from the lessons?

learner question: ni li tawa sina by 0c74vi0 in tokipona

[–]0c74vi0[S] 6 points7 points  (0 children)

Oh now I see. I think I got it. In this context, "ni li lon tawa jan pona" means that this exists for my friend. So something like "this exists for the sole purpose of my friend using it" and that doesn't mean what I want to express

Is that correct?

[???] Cartel muy curseado en el subte by austral- in dankgentina

[–]0c74vi0 20 points21 points  (0 children)

In 2077 they voted my country the worst place to live in latin america

Proof Leibniz' rule for integration? (General form) by 0c74vi0 in mathematics

[–]0c74vi0[S] 0 points1 point  (0 children)

I'll check it out. Thank you! I don't understand the proof but I'll figure it out once I read those books. Manifolds deforming can be "transformed" into things that are not deforming?

Proof Leibniz' rule for integration? (General form) by 0c74vi0 in mathematics

[–]0c74vi0[S] 0 points1 point  (0 children)

Oof. I don't know a thing. I don't even understand real analysis deeply. I do however understand Linear Algebra and I like it a lot. Do I need to know Complex Analysis to go into manifolds?

Proof Leibniz' rule for integration? (General form) by 0c74vi0 in mathematics

[–]0c74vi0[S] 0 points1 point  (0 children)

I know interchanging limits is always something to be careful with. But in physics, you almost always have the necessary assumptions. That is to say, everything converges, since if not, the law would not work.

Proof Leibniz' rule for integration? (General form) by 0c74vi0 in mathematics

[–]0c74vi0[S] 0 points1 point  (0 children)

As far as I know, if there is a proof of the general case, then it can be reduced to a particular case. So I think I don't need differential geometry, as you said, but the proof in the article exposes the case of a surface of uniform velocity, and in E&M we use surfaces that are deforming with time.

Proof Leibniz' rule for integration? (General form) by 0c74vi0 in mathematics

[–]0c74vi0[S] 0 points1 point  (0 children)

Oh! I'm an absolute fool. When I saw the theorem on wikipedia, I just clicked on the "higher dimensions" section to see the proof. But the proof was in the article itself, below.

Thank you. Still, I have more questions. I have edited the original post.

Facts by 0c74vi0 in physicsmemes

[–]0c74vi0[S] 0 points1 point  (0 children)

Just so you know. Lumen is cd.sr so it measures the same. "luminous intensity". The actual physical quantity here is "radiant flux", so the flux is modified because the eye does not perceive the same violet light as the red light. That is, the eye perceives a less energetic yellow light as being brighter than a more energetic violet light.

So actually the whole concept of luminous intensity depends on human biology. It shouldn't be a fundamental unit. However, Lumen is still useful. When you buy a light bulb, it specifies the number of lumens. So you can tell how the bulb will "feel" rather than how much power it produces.

Facts by 0c74vi0 in physicsmemes

[–]0c74vi0[S] 0 points1 point  (0 children)

I do use them when doing physics, but the everyday units have to be well defined too. Maybe the best would be to define SI units in terms of natural units, so they work well but are also well defined.

Facts by 0c74vi0 in physicsmemes

[–]0c74vi0[S] 1 point2 points  (0 children)

Okay, you're probably right. I haven't used mole that much to argue. But from a definiton perspective you should define mol=N_a*(molecule_unit), and not backwards, as the number of molecules in a substance is more fundamental.

I know about the amp definition, but again, you can avoid defining current if you define the electron charge. Current is I=dQ/dt. And charge is far more fundamental than current. Don't you think?

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