The h Bar

2:32 AM

If helmholtz free energy is discontinuous then why gibbs isn't. Ie g=h-Ts. I can't see why internal energy is discontinuous too?

vzn

3:30 AM

@undefined fyi there are a whole set of new cutting edge experiments that show "macroscopic QM behavior"... highly recommend looking into them, and few around here comment or seem to find them remarkable, but its clearly a substantial paradigm shift in play. but yes the idea of waves being mostly a small scale phenomenon has been around for decades... it was once called "the infamous boundary" in one of my favorite popsci physics books... (by Wick)...

Johan Liebert

5:29 AM

Does anyone here knows a case in which energy is not conserved but momentum is?

Semiclassical

5:53 AM

@JohanLiebert As far as kinetic energy conservation goes, the go-to example is an inelastic collision of two bodies

Of course, the total energy is conserved once one accounts for changes in internal energy

Johan Liebert

@Semiclassical i am considering total energy conservation.

0

Q: Does momentum conservation imply energy conservation?

I was trying to figure out situation in which energy is conserved and momentum is not and it was quite easy to find out one case which is of a stone tied to a string moving in uniform circular motion. Then I thought to consider the reverse situation in which momentum is conserved but energy is n...

I have elaborated over here.

Semiclassical

Gotcha

enumaris

6:53 AM

hmmm

undefined

7:06 AM

@vzn thank you, vzn. I'll look into it

Naveen Balaji

9:23 AM

Hey all! I had this doubt- Einstein tensor vanishes identically in (1+1)-D, which means that the stress tensor, S will also vanish (following the expressions as given in Poisson). But, shouldn't S be non-zero to indicate the discontinuity in the first derivative of the metric at the shell? If it vanishes, how does it account for the matter placed on the shell?

John Rennie

9:43 AM

@NaveenBalaji I think there can still be a non-zero cosmological constant appearing on the left side of the equation.

i.e. the equation reduces to:

$$ \Lambda g_{\alpha\beta} = 8\pi T_{\alpha\beta} $$

Naveen Balaji

9:59 AM

@JohnRennie Given the metric, $dr^{2} + \gamma_{tt}(r,t) dt^{2}$, the stress-energy of the source on the screen happen to be null. This metric config. is reflected in the Ricci tensor and scalar since both of these are non-zero. Since the stress tensor, $S_{ab}$, is zero, $T^{\Sigma}_{\alpha\beta} = S_{ab}e^{a}_{\alpha}e^{b}_{\beta}=0$ and this indicates that there is no source right?

John Rennie

No. In 1+1D $R_{\alpha\beta} - \tfrac12 Rg_{\alpha\beta} = 0$ but $R_{\alpha\beta} - \tfrac12 Rg_{\alpha\beta} + \Lambda g_{\alpha\beta}$ can be non-zero.

Johan Liebert

1:53 PM

1

Q: Newtonian-Mechanics .Elastic reflection

Question from the olympiad. Two planes move perpendicular to each other with speeds $v = 1m/s$. A body flies at them with a velocity of $u = 1 m/s$ at an angle $a=45$ to the surfaces of the planes and is elastically reflected successively from each of the planes.No friction Question: Fin...

homework-and-exercises newtonian-mechanics kinematics collision

That user has posted a new question though this time it is a bit different. Should I answer it?

Yuvraj Singh...

2:49 PM

@NaveenBalaji hello.

Jake Rose

@JohnRennie I was at girton last week, they have a bloody swimming pool and I can’t contain my jealousy

John Rennie

3:14 PM

@JakeRose :-)

My niece still has to get the two As and an A* of course.

Johan Liebert

1

Q: I'm stepping down

You are given 4 positive integers: volume of the first container (v1), volume of the second container (v2), volume of the liquid in the first container (l1), and volume of the liquid in the second container (l2). Your task is to move (or "step down", if appropriate) some of the liquid from contai...

code-golf arithmetic integer

Lol (Some serious use of title!)

Novalium Company

3:33 PM

I'm planning to get single super thin wires from one of those (ref to pic) and somehow insulate them individually. How would I do that and is there a better way?

A single wire is as thin as a human hair. Is there a way to insulate it?

What if I dip it in some substance?

What if I dip it in melted hot glue or something?

John Rennie

@NovaliumCompany Lacquer

Novalium Company

How a spray gonna do it?

John Rennie

The spray dries and leaves a solid insulating layer on the wire.

Novalium Company

Alright, thanks.

tpg2114

You'll have to be pretty careful not to burn up single strands of wire

Novalium Company

3:41 PM

I know, that's why I'll go for a bit thicker ones.

tpg2114

I am not an electrical engineer, but a single strand isn't going to carry more than milli-amps

Novalium Company

Can I just buy thick insulated ones? lol

@tpg2114 true, I'm reconsidering making it thicker.

tpg2114

Yeah, of course you can. Thin, thick, braided, not braided

All pre-insulated or not. With thick insulation like your picture, or very thin (like speaker wire)

I guess I should say the "of course you can" is from the perspective of the USA -- maybe it isn't as readily accessible elsewhere, depending on where you might be

Novalium Company

I found what I needed. I have a sample to show the store owner.

tpg2114

You can calculate how thick it needs to be based on your power needs plus a safety margin

Or use a lookup table -- I'm sure there's tables out there since everybody has to size the wire accordingly (thinnest you can get away with is better for weight and cost)

Novalium Company

3:45 PM

I will calculate it.

I need to figure out the other electronics first :P

tpg2114

I was a very bad circuits person. Being colorblind makes reading resistors nearly impossible, and causes lots of burned up hardware.

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