The h Bar

ManishEarth

12:12 AM

@hunter

Hunter

Hey @ManishEarth

ManishEarth

hey :)

Broadness has nothing to do with links, it has to do with the topics covered. The current one asks for notes coming from all categories of physics. Physics is incredibly broad

Emilio Pisanty

Hunter

Sure I understand, but would that also be the case for the topic regarding the books? Why isnt that one considered to be too broad?

ManishEarth

@Hunter Look at the date on that one

The story of the book policy is that initially they were allowed (leading to that books question)

Then they weren't, due to a gradual maturation of network policy

Then we wrote that policy I linked you to, which made them on topic again

@Hunter so the books question links to other books questions. Which is sort of okay, since there aren't that many. Yours asks for links to various notes in all topics of physics -- that is broad

Emilio Pisanty

12:16 AM

@Hunter The overarching books question is also under discussion here: meta.physics.stackexchange.com/questions/5307/…

ManishEarth

We have at max 3 book questions per topic. Not so with notes per topic :p

Hunter

ok, fair enough, is there any possibility of making a wiki post with links per topic?

This wouldnt be too braod?

Emilio Pisanty

@Hunter Not really

ManishEarth

@Hunter Links to what?

Emilio Pisanty

It's just that no one has really had the time to do it

ManishEarth

12:18 AM

Links to questions on physics.SE about lecture notes? That would work, but we don't have any such questions

@Hunter but you don't need to worry, I proposed an alternative

All we do is that we take the notes links from that question, and incorporate them into the community wiki (CW) answers of the book questions (which already list books)

book questions can be easily converted into book+resource ones.

Hunter

Ok, what is the alternative? I think it would really be beneficial for this site to have a post containg links to free lecture notes.

ManishEarth

^

Hunter

ah fair enough, i didnt see your answer.

I actually really like that idea

I believe that one way or another we should have a post containing links to free lecture notes

but i guess we both agree on that

its just that we need to find the best way to do this

hwlau

12:59 AM

@EmilioPisanty True physicists type pure latex!

ManishEarth

@hwlau true physicists define all their latex commands on the spot!

Want to use \vec? Use pure pixel latex :p

Kyle Kanos

1:31 AM

Ugh, \vec is hideous. Just use \mathbf and everyone knows it's a vector

ManishEarth

@KyleKanos yeah

I have a habit of \vec now, but I usuallt renewcommand it to mathbf

Brandon Enright

Huh I always thought sin(x) and sin(x)^2 had different shapes but they're the same shape if you adjust their phase, frequency, amplitude, y offset

This produces the same curve: plot sin(x) with lines, (((sin((x + (pi / 2)) / 2)**2) - .5) * 2) with lines

You learn something new every day.

Kyle Kanos

1:46 AM

@BrandonEnright: How did you discover that?

Or, rather, come across that

Brandon Enright

I was sitting here doing random things and listening to Pandora and an Arctic Monkeys album came up which has a sinewave composed on another sinewave on the album cover and I thought the curve didn't look quite right like maybe it was a bit too steep for a sine wave so I figured it must be sine(x)^2 or something like that. So then I thought "what is the shape of sin(x) anyways?" and plotted it. It looked like the same shape so I just looked at it and figured out what adjustments it needed

So I just looked at sin(x) and sin(x)^2 and adjusted the second to match the first. No real math insight at all.

I think that implies any chain of multiplication of sin(x) and cos(x) can always be reduced to a single sin(x) given the proper adjustments

Yeah, seems that way. This is the same curve: plot (sin(x * 2) / 2) with lines, (sin(x) * cos(x)) with lines

Alright the counterexample is sin(x) * cos(2x) is clearly not a simple sine wave shape

Makes sense. Any product of sine waves of the same frequency reduces to another sine wave. Once you mix frequencies they don't reduced to a single frequency wave anymore.

I'll stop talking to myself now :-p

Kyle Kanos

Hmm

It's interesting though

I do want to point out that you don't need to type with lines when plotting functions in gnuplot (that's what I'm assuming you're using, as it looks that way)

dmckee

@BrandonEnright Don't you recall your basic trig identities? Half-angle and double angle formulas imply this.

Brandon Enright

@KyleKanos Yeah gunplot. "with lines" is a bad habit on my part.

@dmckee Hmm you're right. I hadn't thought about that. It's been too long since I needed any of those. I should look those up again.

Kyle Kanos

2:02 AM

hosted.ap.org/dynamic/stories/A/…

^ Crazy

dmckee

I've been noticing that my upper division student didn't recall them either. Well, the oscillations chapter of Marion and Thorten helped with that.

Emilio Pisanty

2:34 AM

0

A: Community Promotion Ads - 2014

ManishEarth

2:54 AM

@EmilioPisanty btw, this ad is awesome :)

Also the recursion ad :p

hwlau

@BrandonEnright Don't worry, that's is how numerical guys rediscover a mathematical relation

ManishEarth

3:23 AM

@EmilioPisanty Btw, I switched the script over to github.com/Manishearth/Manish-Codes/blob/master/StackExchange/… , and updated the stackapps post

It's more efficient now

But there's no autoupdating

Emilio Pisanty

4:12 AM

@ManishEarth I'm not quite sure what that means.

ManishEarth

6:42 AM

@EmilioPisanty The script is in a different place now, and is better. The old one used to redownload itself often, which isn't necessary

Physics Meta

7:21 AM

0

Q: Is it rude to answer to quickly?

I have recently started partaking in the joys of SE. And at first I aspired to have thousands of rep points and badges, so I started answering questions and asking questions. But now I don't care about the rep points I just like knowing that I am helping someone, the same way some SE user has hel...

discussion

APARAJITA

9:24 AM

Why will that be rude, u r trying to help people , n that's very good

Physics Meta

10:10 AM

0

Q: Why are my questions downvoted?

It seems like just giving an answer or asking a question someone doesn't like causes you to lose reputation yet the people who downvote are not required to list why they did so. At this point after only using the site for a day I am regretting signing up. Most people on here seem nice and provide...

discussion homework down-votes

ManishEarth

2:07 PM

@emiliopisanty Around?

I know you were working on converting old book posts to new ones (so was I, a bit). Any idea what the current status of that is? As in, how many have yet to be converted? I'm thinking of asking for some community effort to wrap it up on meta, if there aren't too many left I'll just do it myself.

Gigi10012

Hello

can i use MathJax in chat?

Emilio Pisanty

2:30 PM

@Manish I'm around but I need to shoot. I'm not sure what the status is. I'll have a look tonight or tomorrow. My overall impression is that there's still quite a few, but I don't know what the basis of that is so treat it as a complete guess.

ManishEarth

3:49 PM

@emilio no need to look into it too deeply, just wanted your general impression, thanks

Arafat

4:45 PM

v^2-u^2=2as .is the law valid in relativistic case?if the answere is no,then how it be modified?

ManishEarth

@Arafat if all the numbers are measured in the same frame, yes

Relativity deals with switching between frames, and doesn't really modify what happens in a given frame

General relativity is a different beast, you'd have to throw in a couple of $g_{\mu\nu}$s into that equation

dmckee

4:57 PM

@Arafat Be aware that that equation assumes constant acceleration, and it won't be constant in cases involving very high relative velocities without great effort on the part of the experimenter. Indeed there are absolute limits on how long a constant acceleration can be maintained.

Physics Meta

9:49 PM

1

Q: How tell the difference between the following modes of unresponsiveness to your question: unnoticed, unanswerable, trivial, confusing, or apathetic?

How does one distinguish between any of the following reasons why he or she has not received a response to his or her question: (1) The question is unnoticed by many. (2) Not many feel confident or qualified to provide an answer. (3) The question is too trivial. (4) The question is too confus...

feature-request

Gigi10012

10:03 PM

Hello. I have one question: I want to solve shrodinger equation for a photon. here's what i did:
$$
E\Psi = - \frac{\hbar^2}{2m} \nabla^2 \Psi + V\Psi
$$
$$
-\frac{2Em}{\hbar^2} \Psi=\nabla^2\Psi - \frac{2mV}{\hbar^2} \Psi
$$
$$
\nabla^2\Psi - \frac{2mV}{\hbar^2}\Psi +\frac{2Em}{\hbar^2} \Psi =0
$$
$$
\nabla^2 \Psi -\frac{2m}{\hbar^2}\left(V-E\right) \Psi = 0
$$

$$
\nabla^2\Psi +\frac{2m}{\hbar^2}(E-V)\Psi=0
$$

$$
E = \hbar f
$$

$$
\nabla^2\Psi+\frac{2m}{\hbar^2}(\hbar f-V)\Psi =0
$$

$$
V =0

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