The h Bar

3:03 PM

45 minutes until my presentation :/

O_O

@ACuriousMind you know how in german, we often call small effects "eine (kleine) Störung" - any idea how to translate that into english?

ACuriousMind

@Sanya a small perturbation?

Sanya

wonderful, thanks - it just didn't come to my mind

ACuriousMind

...great. Just when I thought I had figured out that "M-theory" really just means 11D SUGRA, this paper starts saying that the phenomena discussed are only visible in "full" M-theory and not the SUGRA approximation. WTF is "full M-theory"?

Sanya

:| I'm an experimental physicist so ... :| sorry :<

Kartik Watwani

3:14 PM

What does this line mean when referring to forward bias applied to pn junction "the equilibrium is disturbed between the thermally generated carriers and the repelling electric field of the n-doped emitter depletion region"?

ACuriousMind

@Sanya That's nothing to be sorry about ;)

I guess I'll try asking on the site

Although the track record of getting useful answers to my questions is not good :P

Sanya

@ACuriousMind well, I feel that you're always helping me and there's nothing I can give back

@ACuriousMind can you top my 0% answered questions? :D

ACuriousMind

@Sanya lol, no

I have gotten some answers here

Kartik Watwani

@ACuriousMind @Sanya anybody can answer my question?

ACuriousMind

Alas, I've also asked more than one question :P

Sanya

3:19 PM

@ACuriousMind :P

@KartikWatwani I'm as confused by that line as you are, even though I do have some idea of what a pn-junction is

Kartik Watwani

@Sanya I have also spent time on pn junction in last two days but still I am not getting this line .I read this line while reading BPT on wikipidea

Sanya

my advice would be - if you feel halfway confident that you know how a pn-junction works, ignore the sentence, sometimes some explanations in a book just do not make sense to everyone and as long as you get the way it works, that's the main point

Kartik Watwani

I read this line while reading BPT on wikipidia.So I think it will hinder my complete understanding of transistor so I stopped looking for the explaination. @Sanya

John Rennie

4:18 PM

@ACuriousMind I'm not sure I see that interpretation, but I've reopened the question anyway.

Secret

4:35 PM

[Abstract algebra] Improved algorithm, now I can construct any associative structure on the fly!

another interesting note is note how cbS and Scb reminds of cosets in group theory. Perhaps there is a geometric interpretation to associativity

One reason I like abstract algebra: They are so bare bone to the point and extremely general that once something is understood, it can be rapidly optimised by conversion into an algorithm

vzn

5:07 PM

@whatwhatwhat hi welcome to the chat. we have a special speaker session, always looking for volunteers, your topic seems worthy, plz consider :) meta.physics.stackexchange.com/questions/7783/…

John Rennie

5:30 PM

@ACuriousMind yes, I did mean venomous :-)

Though maybe adders are poisonous. I have never eaten one so I wouldn't know :-)

John Rennie

5:54 PM

Ooh! Echoes from the Abyss: Evidence for Planck-scale structure at black hole horizons

Almost certainly a false alarm, but .. well, just maybe ...

ACuriousMind

6:27 PM

@JohnRennie @Qmechanic It's been a while, but you voted to close here. OP then re-asked the exact same question here not 15 minutes later. In that case, no vote to close occured and John even answered it. I'm confused by this chain of events.

user246160

@ACuriousMind That was my question. You marked them as duplicates, but they are not duplicates. One is about linear velocity while the other is about angular velocity.

ACuriousMind

Oops, yes, I see that now

user246160

@ACuriousMind BTW I still cannot understand why it was closed as a homework problem...it was purely conceptual....

ACuriousMind

@TheStackExchange The first version of your first question asked us if your reasoning is correct, which is off-topic as a "check-my-work question", cf meta.physics.stackexchange.com/q/6093/50583

I don't particularly like the revised versions because they show no research effort, but I'd say they are not off-topic as homework-like. However, Qmechanic seemed to disagree.

user246160

@ACuriousMind Yes I know the first version was not suitable for the site. And it has been nearly two weeks since I edited it to fit the rules....what type of research effort are you seeking in the question ? (Just curious)

user246160

6:37 PM

Moreover after editing it I also left a comment whether it fits the rules...and no one replied....

Sanya

@ACuriousMind on the other hand, there is no close reason for insufficient research effort, is it?

2

ACuriousMind

@Sanya That's a contentious issue (e.g. meta.physics.stackexchange.com/q/6001/50583) and why I reopened the question after it was pointed out it's not a duplicate.

Sanya

@ACuriousMind don't understand me wrong, it often annoys me more than e.g. well-written homework questions; but I've seen enough of them and I've had multiple declined flags which were just "do my research for me"

John Rennie

@ACuriousMind I think I answered the second question before I saw that the first question had been edited.

I VTC'd the original pre edit, and by the time I saw the edit I had already answered the repost. So there seemed little point in reopening the first question.

user246160

@ACuriousMind I would request you to follow a uniform policy. If you want to close for lack of research close both the questions or keep both open. They are similar questions in nature apart from one being about "angular" and the other "linear". And I would request moderators to point out the exact mistake in framing of a question before closing them. I edited the question and kept waiting for 2 weeks for a reply.

user246160

6:45 PM

@JohnRennie The original question(after edit) was different from the the question you answered. So I do not understand why you decided to keep it closed.

Qmechanic

@TheStackExchange : In general, it is best not to ask very similar-looking questions in rapid succession, or crossposting, as this is likely a waste of time for potential answerers.

John Rennie

@TheStackExchange are we talking about the same two questions? The two questions linked in ACM's post are near identical.

user246160

@Qmechanic Yeah they are similar questions I agree. But they are not same questions. I asked them separately because linear velocity and angular velocity are two different concepts.

John Rennie

21 mins ago, by ACuriousMind

@JohnRennie @Qmechanic It's been a while, but you voted to close here. OP then re-asked the exact same question here not 15 minutes later. In that case, no vote to close occured and John even answered it. I'm confused by this chain of events.

user246160

@JohnRennie How is linear velocity identical to angular velocity ? How are they " same two questions " ?(Yeah I am talking about the two ACM linked)

John Rennie

6:51 PM

@TheStackExchange I'm looking at those two questions and neither has the word linear in. That's why I wonder if we are looking at the same questions.

0

Q: In circular motion of a particle is the velocity of particle always perpendicular to the centripetal acceleration?

In circular motion of a particle is the velocity of particle always perpendicular to the centripetal acceleration? Are there any exceptions? Why or why not ?

0

Q: In circular motion is the angular velocity vector always perpendicular to centripetal acceleration?

In circular motion is the angular velocity vector always perpendicular to centripetal acceleration? Are there any exceptions? Why or why not?

newtonian-mechanics kinematics vectors rotational-kinematics

user246160

@JohnRennie But one had the word "angular" in it. And when we talk about velocity we most generally mean "linear velocity".

Qmechanic

@ACuriousMind : I agree that it is not hw per se, although elementary. I don't now recall the actual motivation for my vote, but I could have mistakenly though they were duplicates, and achronically switched the role of duplicates for flexibility.

koolman

I have a MS word file of subject chemistry typed in Hindi language . How can I translate the Hindi language into English language of the file ?

Can anybody suggest me a site

John Rennie

@TheStackExchange Hmm, OK, though I think most readers will fail to see that distinction unless you emphasise it. Anyhow the answer is no because there can be an arbitrarily large tangential acceleration.

@koolman Google Translate?

koolman

@JohnRennie text written in tabular form cannot be translated

user246160

6:58 PM

@JohnRennie But tangential acceleration can only accelerate it in tangential direction, keeping it perpendicular to the radial vector....

user246160

Could you please elaborate a bit ?

user246160

@Qmechanic Now that you realize that they are not duplicates, could you re-open it ?

John Rennie

The total acceleration is the sum of the tangential and centripetal acceleration and can point in a range of different angles.

Incidentally I have voted to reopen the question.

Oh hang on, sorry, I didn't read your question properly.

user246160

@JohnRennie It is hard to visualize that. You mean to say that due to arbitrary tangential acceleration the particle stops circular motion? I know that net accn may be at any angle but how can you be certain that linear velocity changes its angle from perpendicular...

John Rennie

By definition in circular motion the velocity is always tangential so it is necessarily normal to the centripetal acceleration, though not to the total acceleration.

user246160

7:04 PM

@JohnRennie I get it now. Thanks.

Bernard Meurer

@ACuriousMind I summon you

I need LaTeX help

ACuriousMind

What do you need?

Bernard Meurer

So, I'm making a small writeup that has theorems, definitions, proofs, so on

And I wanted to make sure that the text for said things all started in a newline

so I was pointed to use the ntheorem package

but that conflicted with amsthm

So I removed amsthm, and was left without a proof environment

So I tried making my own, like such

\theoremstyle{break}
\newtheorem{theorem}{Teorema}
\newtheorem{definition}{Definição}
\newtheorem{proposition}{Proposição}[theorem]
\newtheorem{lemma}{Lema}[theorem]
\theoremstyle{nonumberplain}
\theoremheaderfont{\itshape}
\theorembodyfont{\normalfont}
\theoremseparator{.\,—}
\theoremsymbol{\ensuremath{\color{lightgray}\blacksquare}}
\newtheorem{proof}{Demonstração}

But I don't get a nice QED square when the proof ends :(

ACuriousMind

Removing amsthm doesn't sound like a wise decision

What exactly do you mean that the text starts in a newline? Do you want the "Theorem X.Y.Z" on its own line? Why?

Bernard Meurer

Like this

See how there is like a title, and then the theorem or w/e the case may be

ACuriousMind

7:18 PM

Ew

Bernard Meurer

Yeah, I know

It's all because I wanted this:

to look ok

I guess I'll just revert to not using ntheorem

and using a newline on that specific case

Færd

8:13 PM

Why does the poster of this answer suppose that the center of mass coincides with the center of the geometrical shape of the chair?

> for the square chair the distance from the centre to the edge is d while for the triangular chair it's dtan30∘ or about 0.58d. That means on the triangular chair you can only lean half as far before you fall over

And why is the distance between the center to the edge is confused with how "far" you can lean back?

Maybe I'm missing something?

(correction: shape of the chair → shape of a back-less chair)

DanielSank

8:36 PM

Apparently our group volunteered to sort abstracts for the APS March meeting.

dmckee

8:52 PM

@DanielSank That's going to be fun. Who's providing the pizza and beer?

There is going to be pizza a beer, isn't there?

Abcd

9:21 PM

Can I ask a short question?

I wanted to ask that how to determine the direction of magnetic field at the centre of the cardboard when current carrying loop wire passes through it ?

heather

hello everyone

Abcd

@heather can u answer me?

Sanya

@heather good evening

Abcd

hii everyone

heather

@Abcd, nope. I might point out a few rules of chat etiquette that'll help you out though. 1. No need to ask if you can ask, just ask =) 2. Don't randomly ping people; that just annoys people. 3. If some can and wants to help, they will. Good luck with your question!

Abcd

9:31 PM

Can someone pls answer my question

heather

@Sanya, o/

@Abcd, also, please don't say something like "can you answer x" every 5 seconds; you can re-ask, just don't do it super frequently. People can read the transcript or scroll up a few messages.

Abcd

k @heather !

heather

@Abcd, like I said, good luck with your question =)

Sanya

@Abcd en.wikipedia.org/wiki/… should help :)

Abcd

9:56 PM