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bio website mathandcode.com/programs
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age 21
visits member for 2 years, 10 months
seen 8 hours ago

Jun
25
comment A course in Lagrangian Mechanics
@KyleKanos I recommend the book, and he does stuff in there such as deriving [truly, not in a handwavy sense] the E.L. eqs from the least action principle (in the same way Euler did, it turns out), finding the rate of precession given angular momentum and an external torque, and plenty of other good math stuff. So it's far from popular. It does lack in problems a bit though.
Jun
21
comment Calculating the resistance of a 3D shape between two points
"Derivation of the whole Drude model"?? There's no need to be so dramatic, it's maxwell+$J=\sigma E$!
Jun
20
comment Calculating the resistance of a 3D shape between two points
This is a pretty poor answer. It doesn't show how this follows from Maxwell's equations, which was part of the question.
Jun
17
comment Derivation of law of inertia from Lagrangian method (Landau)
@AloizioMacedo turns out this is a very annoying question you asked! Let me know if my most recent edit "helps".
Jun
17
comment Derivation of law of inertia from Lagrangian method (Landau)
@AloizioMacedo Sorry, I was actually thinking about fixing that. The goal of classical mechanics is to uniquely determine the equations of motion. I'll update my post.
Jun
17
comment Derivation of law of inertia from Lagrangian method (Landau)
If $L=0\cdot \dot{x}^2$, $\dot{x}$ can be anything and satisfy $L=0$, and that's the issue the OP is getting at.
Jun
16
comment Derivation of law of inertia from Lagrangian method (Landau)
$L=0$ doesn't imply $\dot{x}=0$. Actually, it implies absolutely nothing!
Jun
14
comment Reduced gravity flight's affect on convection based cooling
operation of a macbook pro in "the vomit comet" [or similar aircraft] or in a regular aircraft? On a regular aircraft there should be no difference.
Jun
3
comment How do I actually calculate the Lorentz transformation of a field strength tensor
Hi Josh, there's a mistake here! I think you're forgetting $f_{11}$ must be a matrix. The correct result is $\{\{\lambda f_{11}\lambda,\lambda f_{12}\},\{ f_{21}\lambda,f_{22} \} \}$
May
24
comment Best coordinate system for Projectile motion
@SohailAhmed I mean that the gravitational field is treated as a constant $g$, as opposed to a gravitational field which might go like $\frac{\hat{r}}{r^2}$. The second case is a lot more complicated.
May
19
comment About field gradient
Hi @victorbg, "gradient" can mean many different things. If someone is reading about a "gradient in the magnetic field", they probably mean "gradient" in the more general/english sense of the word, not the "turns a scalar field to a vector field" sense of the word. So, for example, if someone had an experiment with a "large magnetic field gradient", I would think something like the magnets involved in the Stern-Gerlach experiment en.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experiment . Also relevant: en.wikipedia.org/wiki/…
May
18
comment Can Lagrangian mechanics be justified without referring to Newtonian mechanics?
It might also be worth mentioning what L&L do in the first book. IIRC they get pretty far just assuming the eqs of motion stem from an action principle & respect galilean invariance.
May
17
comment Relativistic rigid motion
@facenian It's true that you'd have to take care to avoid letting particles travel faster than the speed of light. Other than that, there is no contradiction.
May
11
comment Took a picture of my laptop screen with my iPhone. The blue pattern in the image seems to magnetic lines. How is this possible?
Was your camera flash on? Also, can you check if the same pattern appears if you take a picture of a piece of paper or some low light/contrast thing?
May
7
comment Simultaneity and quantum indeterminism
Hi @MoziburUllah, in the terminology anyone is using if they say "relativity of simultaneity", events are defined to be simultaneous if events $(t_1,x_1,y_1,z_1)$ and $(t_2,x_2,y_2,z_2)$ have $t_1=t_2$, which is of course not a lorentz-invariant concept, hence "relativity of simultaneity".
May
6
comment Simultaneity and quantum indeterminism
@JohnDuffield All the articles I get are about the constancy of the speed of light? Yes, if you don't assume the length of a meter (SI convention) is constant, you run into all sorts of problems.
May
6
comment Simultaneity and quantum indeterminism
@Abc2000ro Exactly - because the notion of simultaneity of two spacelike separated events has no inherent physical meaning. The physical meaning comes about when you establish real, physical clocks, and then collect the data at some point.
May
2
comment Do the same equations of motion imply the same Lagrangians?
I feel like this doesn't really answer the question. It gives a sufficient condition for generating the same equations of motion, but not (as AV23's answer shows) a necessary one.
Apr
24
comment How to simulate pendulum movement with high amplitude
khanacademy.org/computer-programming/forphys/6505289796943872 the "degrees" function turns radians into degrees, (multiplication by 180/Pi) which the trig functions need. no further explanation needed
Apr
23
comment Parabolic slide
@Shadock also, since $\dot{x}(x_0)=0$ you'll run into an integral with a singularity at one bound of integration, but it has to be an integrable singularity. If it puts you off too much just take $\dot{x}(x_0)=\varepsilon\to 0$.