Astronomy/Astrophysics

23 Mar 2025 05:47

Everything up to 18th Century physics is more or less classified as "classical mechanics"
So if you want to say, I'm not taking relativity and quantum into account.
All you have to say, is in
"Classical Mechanics"

Astronomy/Astrophysics

23 Oct 2024 20:37

Astrophysical Journal in the news
Webb finds candidates for first young brown dwarfs outside the Milky Way

Near the outskirts of the Small Magellanic Cloud, a satellite galaxy roughly 200,000 light-years from Earth, lies the young star cluster NGC 602. The local environment of this cluster is a close analog of what existed in the early universe, with very low abundances of elements heavier than hydrogen and helium.

Astronomy/Astrophysics

23 Oct 2024 16:28

Astrophysical Journal in the news
Astronomers use JWST to study hydrodynamics and nucleosynthesis of jet-driven supernovae

A study published in The Astrophysical Journal presents new simulation results of supernova explosions that explain the latest observational data from the James Webb Space Telescope (JWST).

Astronomy/Astrophysics

23 Oct 2024 03:49

New members please go through the rules. You can see the rules by typing /rules. Try to have productive discussions here. Please check the guidelines for Asking Good Questions

Astronomy/Astrophysics

22 Oct 2024 07:34

Very rough of him lol, the guy i asked (CondMat-PhD in US) said that it's taught in second course on electrodynamics after one has done relativistic electrodynamics.

Astronomy/Astrophysics

22 Oct 2024 07:30

pretty easily ig (observe the form of the expression).

Astronomy/Astrophysics

22 Oct 2024 06:39

Oh where did you find the question?
So it is V(r') as you said not V(x')

Astronomy/Astrophysics

22 Oct 2024 06:19

https://youtu.be/RaGUW1d0w8g?si=YVihYDwDZpYBRvYJ

Astronomy/Astrophysics

22 Oct 2024 06:17

It actually used so called Green's first & second identity.
Resources to understand it :

farside.ph.utexas.edu/teaching/jk1/Electromagnetism/node22.html

galileoandeinstein.phys.virginia.edu/Elec_Mag/2022_Lectures/EM_07_Electrostatics_II.html

Astronomy/Astrophysics

22 Oct 2024 05:36

Is giant arc and this big ring different ??

Astronomy/Astrophysics

22 Oct 2024 05:29

Ohkay, considering this...i don't know vro, never encountered potential in form like this (neither some theorem in vector calculus).

But i will ask it in other groups of advanced physics.

Astronomy/Astrophysics

21 Oct 2024 22:41

Deriving electrostatic potential

Astronomy/Astrophysics

21 Oct 2024 20:38

just as an example we consider the earth to be a ring shaped structure then which path will the moon take? scientist consider many things and what will happen with it just out of curiosity. but in general no space object can hold the ring like structure because the COM will be outside of the body and it will deform into a sphere or almost a sphere with a slight bend in the equator.

Astronomy/Astrophysics

21 Oct 2024 19:54

I think its own gravity which makes the mass loss

Astronomy/Astrophysics

21 Oct 2024 19:52

I think we need a redefined model of gravity other than force (as per Newton) or space time curvature (as per Einstein) which has many flaws in it I think it is as similar as energy and also something which gives out energy will loss its mass over the time (I suspect even gravitational energy from the object makes it to loss its mass)

Astronomy/Astrophysics

23 Mar 2025 05:46

That is also a part of
"Classical Mechanics"

Astronomy/Astrophysics

23 Oct 2024 19:52

So here's how it is done applying greens second identity:

Let's start with poisson's equation:

We know that the electrostatic potential V(r) satisfies Poisson's equation:

∇²V(r) = -ρ(r)/ε₀

And greens second identity which is stated as:
∭(u∇²v - v∇²u) dV = ∬(u∇v - v∇u) ⋅ dS

Now let u = V(r') and v = 1/R = 1/|r - r'|

Then ∇²v = ∇²(1/R) = -4πδ³(r - r') (This is immediately obvious from the Laplacian of the inverse distance function, where δ³(r - r') is the Dirac delta function).

And ∇²u = ∇'²V(r') = -ρ'(r')/ε₀ (from Poisson's equation)

Plugging these into Green's identity:

∭(V(r')∇'²(1/R) - (1/R)∇'²V(r')) dV = ∬(V(r')∇'(1/R) - (1/R)∇'V(r')) ⋅ dS

∭(V(r')(-4πδ³(r - r')) - (1/R)(-ρ'(r')/ε₀)) dV = -4πV(r) + ∭(ρ(r')/ε₀R) dV

Rearrange and Solve for V(r):

V(r) = -1/4π∬(V(r')∇'(1/R) - (1/R)∇'V(r')) ⋅ dS + 1/4π∭(ρ'(r')/ε₀R) dV

using the fact that ε₀ = 1/(4πk), and generalizing ρ'(r')/4πε₀R = ρ(r')/R we get the desired result:

V(r) = ∭(ρ(r')/R) dV + (1/4π)∬((1/R)∇'V(r') - V(r')∇'(1/R)) ⋅ dS

The volume integral represents the potential due to the charge distribution throughout the volume.
The surface integral accounts for the potential due to any charges on the surface of the region.

Astronomy/Astrophysics

23 Oct 2024 08:50

that's tough!!!!!!!!

Astronomy/Astrophysics

22 Oct 2024 09:29

Ok I will try it, thanks

Astronomy/Astrophysics

22 Oct 2024 07:32

in my opinion it should be written as V(r), potential being a function of position vector not of its first derivative (if prime notation isn't used for field points as used by Griffiths).

Astronomy/Astrophysics

22 Oct 2024 06:40

Oh yeh so we can derive the expression using greens identity?

Astronomy/Astrophysics

22 Oct 2024 06:38

No it is our instructor who made it up, I didn't even see the equation from any ED book. The teacher just come up with it and ask us to derive it😅

Astronomy/Astrophysics

22 Oct 2024 06:19

This "g" is actually Green's function lol.

Astronomy/Astrophysics

22 Oct 2024 05:48

here is the LaTeX version 😉

Astronomy/Astrophysics

22 Oct 2024 05:35

If you made-up it on your own then it's wrong ig (in terms of formulation), "F = V'(x)" is one-dimensional case while you're using V(r') down there so why not V(x') there too or using "r" everywhere ?

Astronomy/Astrophysics

22 Oct 2024 00:25

Astrophysical Journal in the news
Betelgeuse Betelgeuse? Bright star Betelgeuse likely has a 'Betelbuddy' stellar companion

One of the brightest stars in the night sky, Betelgeuse, may not be on the brink of exploding as a supernova, according to a new study of the star's brightening and dimming. Instead, recent research shows that the observed pulsing of the starlight is probably caused by an unseen companion star orbiting Betelgeuse.

Astronomy/Astrophysics

21 Oct 2024 21:58

can anybody describe me this ( i am not even getting a single clue on what to do)

Astronomy/Astrophysics

21 Oct 2024 20:34

that's just a theory every unique shape has its own name
the spherical spere you're talking about is the most accepted one till now, but there are some other speculations too you know

Astronomy/Astrophysics

21 Oct 2024 19:53

This theory can be better linked with Hawking radiation (which is not yet proven and also this theory violates the mass energy equivalence law for a short period of time)

Astronomy/Astrophysics

21 Oct 2024 19:49

Wow that a fascinating idea Im also thinking that everything in this universe is made up of same thing with different manifestation just like an atom having proton electron and neutron and only the numbers and composition changes the property of every elements