The h Bar - 2014-01-20

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12:26 AM

@ArjunNagarajan Hooke's law is the empirical rule for the force needed to compress a spring (or the force with which the spring pushes back): F = -k \Delta x. Where k is called "the spring constant" and is a property of the spring in question.-

@ArjunNagarajan Impedance matching is a technique for making two parts of a AC circuit get along well. If the impedances are mismatched it the signal will be attenuated and reflected at the boundary between the parts of the system.

5 hours later…

user54412

5:39 AM

@ManishEarth Hackathon = shortish period of time (24-48hr) where you code with your fellow computer geeks, eating junk food and not bathing

user54412

:P

7:22 AM

@ChrisWhite lol

We coded in my department lab (the CS dept, which was helping MS organize the event, has a large but stuffy lab with annoying Net connectivity). The girls' hostel canteen is nearby, and there actually is good food there (not just junk food), so not totally true on that part

But we did have a lot of chips to munch on throughout. The organizers provided food, but for us stable Internet (Git, and MSDN/MDN+Google+Stack Overflow) was way more important.

3 hours later…

Waffle's Crazy Peanut

10:43 AM

@dmckee Meh, I hate him!!! - especially because I had to cuddle his theory throughout my first year of ~~hell~~ >_<

3 hours later…

1:31 PM

Gaaaahhh!!!!

Start of term!

user image

Post closures as off-topic tagged homework, by date.

data.stackexchange.com/physics/query/edit/161237#graph

Four times the rate we had in December :(.

Impressive

@EmilioPisanty What language is used there?

Waffle's Crazy Peanut

@KyleKanos SQL

Hmm. Wonder if it's worth learning yet another language to find some data.

Waffle's Crazy Peanut

@KyleKanos There are already lots of data. Learn by browsing through them :P

Yeeeeaahh, I'm trying to graduate.

Waffle's Crazy Peanut

1:41 PM

Hehe :D

And making the data.SE graph work is annoying

@ManishEarth Another reason for me to say No thanks

@KyleKanos sql is pretty simple actually. It's a query language, not a programming one. But JOINs aand GROUP BYs can become quite icky

Plus I have to figure out super time stepping today

heh

1 hour later…

Waffle's Crazy Peanut

2:43 PM

@ManishEarth: Right now, I'm uploading my video... But, I forgot about attributions

I mean, I used 3 or 4 images from the internet (which display only for about 4-8 seconds)

Should I attribute them in the video?

@Waffle'sCrazyPeanut Even if there's a copyright on the image, your use ought to apply to the fair use clause.

Waffle's Crazy Peanut

@KyleKanos Those images don't have any copyrights on them

2 are from wiki, they don't have copyrights

@KyleKanos: Oh, teaching is there - so, it's not a problem I guess :D

Thanks :)

Everything on wiki is GPL'd, meaning it's free to use!

Waffle's Crazy Peanut

Oh, alrighty then :D

Now, there's only one problem

As a no-good-in-English speaker, my accent sucks (in my video) :/

Hi folks, is my answer correct about the following figure?

user image

Waffle's Crazy Peanut

2:57 PM

@CodeMocker which answer?

@KyleKanos Or for a slightly more structured approach google "software carpentry". But I mostly do databases by money-see-monkey-do, just like Waffle's says.

Right after the red thread is cut, the instantaneous acceleration of $m_4$ is $\frac{g(m_1+m_2-m_3-m_4)}{m_4}$.

the instantaneous acceleration of $m_1$, $m_2$ and $m_3$ is 0.

@dmckee Getting paid is a good reason to do something.

3:18 PM

@KyleKanos not everything. The images have individual licencing

Wikipedia:Image use policy

This page sets out the policies towards images—including format, content, and copyright issues—applicable on the English-language edition of Wikipedia. For information on media in general (images, sound files, etc.), see . For information on uploading, see , or go directly to . For other legal and copyright policies, see . Requirements Whenever you upload an image, you should meet the following minimal requirements. # Always tag your image with one of the . When in doubt, do not upload copyrighted images. # Always specify on the description page where the image came from (the origin,...

They have fair use images on WP too.

Uploaded images must fall into 1 of 4 categories: (1) your own work (which you have to declare as GPL) (2) fair use work (which you can use anyway) (3) Public domain (which is free for all anyway) or (4) made by someone else but GPL'd

"fair use work (which you can use anyway)" -- that's the point, fair use policy is very annoying and hard to comply with

AFAICT, Fair Use applies so long you are not trying to make money off the use of the content

3:23 PM

Read through WP:NFC

Wikipedia:Non-free content

Wikipedia's goal is to be a free content encyclopedia, with free content defined as content that does not bear copyright restrictions on the right to redistribute, study, modify and improve, or otherwise use works for any purpose in any medium, even commercially. Any content not satisfying these criteria is said to be non-free. This includes all content (including ) that is fully copyrighted, or which is made available subject to restrictions such as "non-commercial use only" or "for use on Wikipedia only". (Many images that are generally available free of charge may thus still be "no...

I'm skimming through now (started before you linked too)

heh

Now note that the NFC as Wikipedia has it is to satisfy international law. If you look at the fair use clause I linked previously, it says Examples of fair use include commentary, search engines, criticism, parody, news reporting, research, teaching, library archiving and scholarship.

If Waffle is using it to teach, fair use applies 100%

Waffle's Crazy Peanut

3:50 PM

@KyleKanos Of course, I am using it to teach :D

Is physics ultimately just about how things move and what are the related concepts for that ?

How can this lead to knowing everything about the universe ?

Waffle's Crazy Peanut

@L-L Actually it's "how" things work (move is just a part of it) ;-)

if it is just ultimately mechanics

@Waffle'sCrazyPeanut Can you quote an example where things aren't ultimately related to some sort of motion

I mean even in classical mechanics

Waffle's Crazy Peanut

@L-L quantum mechanics :P

It hangs with probabilities

the study of fields and forces ultimately originated from knowing $\vec{r(t)}$ of the particle

@Waffle'sCrazyPeanut Yes but ultimately just trying to which part of space and time a particle is likely to occupy at an instant, which just turns out to not be predictable in absolute terms

Of course you get to meet many exotic particles like photons etc. but ultimately just mechanics is there at the roots

Even in relativity

and QFT

Waffle's Crazy Peanut

4:01 PM

Okay, do you really wanna know something, or is this a debate? :D

No, I want to know

I mean actually when I thought about it, it just came down that everything is about how a particle moves and what are the related concepts to explain that whereas I was under the impression that physics is much more than that

and another question I have in mind

2

Q: Landau's argument for dependence of Lagrangian on magnitude of velocity

In chapter 1, of Landau-Lifshitz Mechanics' book, Landau through isotropy and homogeneity of space and homogeneity of time proves that the Lagrangian must depend of magnitude of velocity of the particle. This seemed fine. But he didn't give a reason as to why it must depend of $|v|^2$ and not on...

classical-mechanics lagrangian-formalism

Related to an answer to this question. Here simplicity is used as a reasoning for justifying why a particular answer should be correct

I am not sure if this argument is strong enough

Waffle's Crazy Peanut

@L-L What do you mean by "much more than that?" You just said that everything has motion in its roots. Then? o_O

@Waffle'sCrazyPeanut I want to know if there's something that I am missing

Well, motion of energy to be precise(r).

:)

Hee hoo

Waffle's Crazy Peanut

4:27 PM

@KyleKanos: Upload complete: youtu.be/rw9rrVR453A

(Pardon me with my style of speech :D) - I did try :)

@AmalMurali Hey!!! :D

@Waffle'sCrazyPeanut You need a British accent.

Waffle's Crazy Peanut

@KyleKanos: Dunno what accent I'm using now :P

Not a British one.

Waffle's Crazy Peanut

Hah!!! :D

@KyleKanos Well, that's all you ca expect from an average Indian :D

@Waffle'sCrazyPeanut This is true.

I thought the video was good. A little odd to start a lecture series with acceleration, but it still worked.

Waffle's Crazy Peanut

4:40 PM

@KyleKanos And, I can assure you that out of 40 or something students in our class, about 5 speak fluent English, about 10 try and suck all the time (like me), while the rest don't even bother trying -_-

@KyleKanos Yeah, I thought of starting with basic inertial items like velocity & acceleration, but that's old school <-- everyone would've learned that. So, I skipped into :D

And, thanks for the review :P

1 hour later…

5:50 PM

-1

Q: How many females visit this site?

Recently there has been a lot in the media about how to get more females into studying the sciences, especially physics and mathematics. I have three related questions that I think may help. Are you a female with tertiary scientific qualifications visiting this site? Are you a female without ...

discussion statistics

2 hours later…

Brandon Enright

7:56 PM

I feel like a total asshole for VTCing that "How do you explain to a 6 year old..." question.

@BrandonEnright Did you VTC before it became a popular question?

Brandon Enright

No I just woke up, saw it, and felt it is off topic. Just VTC'd 5 min ago.

Lame. I thought it was a good question.

Brandon Enright

I wrote a detailed close reason.

Reading...

That's debatable.

Gotta suck to be a mod to clean up the dumb comments.

Brandon Enright

8:02 PM

It seems like they don't even try to cleanup bad comments on stackexchange anymore

I see questions with 200 comments and half should be removed

I think it's because SE is just too big

There constantly 100k questions in the close queue

Brandon Enright

@KyleKanos That's CRAZY.

Yep. There's 6.5 million questions posted there

Now compare that to our ~28k

Brandon Enright

I know they get something like 500 questions a day. I wonder if their high-rep to low-rep user ratio is worse than ours?

We have very few active > 3k users but I could totally imagine our ratio being better than theirs.

I imagine that it is worse than ours.

There's 68 thousand pages of users there: stackoverflow.com/…

Brandon Enright

8:06 PM

The SE dev should make the page count overflow and wrap at 65535 just for entertainment purposes

Page 27353 is the transition from 1 rep to 2+ rep: stackoverflow.com/…

Almost 40800 pages of 1 rep users.

Brandon Enright

Man okay their ratio has to be worse than ours.

Hah...with 36 people per page, that's 1.5 million 1 rep users on SO.

Brandon Enright

Reminds me of an ultra-modern version of the beach boys song with the line "two girls for every guy"

There is a place out there. Not California but StackExchange where all of your flagging and voting dreams can come true.

Page 1519 is where the transition occurs for 999-1000: stackoverflow.com/…

What is considered "high rep"?

Brandon Enright

8:18 PM

3k is where the rep transition make a big difference for closing stuff

and 10k is where it makes a really big difference for most site cleanup needs

Okay...I'm gonna do a bit more research on SO real quick

Brandon Enright

@KyleKanos Manual binary search.

@BrandonEnright Really? I never really found much use for 10k.

@BrandonEnright Precisely

@BrandonEnright It's funny how so many people don't know that trick

Brandon Enright

8:20 PM

@ManishEarth If you mean funny as in "haha the world is fucked" then yeah it's hilarious.

yep

:P

SO has (all numbers approximate) 5100 users at 10k+, 19,400 users at 3k+, 54,700 at 1k+ and 2.4 million total users

@KyleKanos And currently, 400 questions with bounties. Math has 50, we have 3. We should rethink this ad: meta.physics.stackexchange.com/a/5296/8563

That's an almost 1:500 for 10k+ and 1:123 for 3k+

@EmilioPisanty Maybe make it an order-of-magnitude thing? Something like There are approximately 10 questions with bounties

Brandon Enright

@KyleKanos They it wouldn't need to be a dynamically generated thing. It could just be a static image.

8:32 PM

@BrandonEnright Not a bad idea

@KyleKanos No, really, though: we need to consider whether we should be advertising this. Other sites have a much higher count there; if someone comes from there and pops their head into physics, they'll think "ah, so there isn't really that much there...". Maybe we'd do better with something like this one: meta.mathematica.stackexchange.com/a/1168/1000.

@EmilioPisanty That wasn't meant to be a serious comment :(. But I do like your suggestion more of using the unanswered questions as a draw. I've actually been meaning to make a meta post about them, just haven't gotten around to it

8:55 PM

0

Q: A change of units in Bethe formula

I'm reading through the following paper: Monte Carlo simulation of non relativistic electron scattering by W. Williamson and G. C. Duncan. In the following paragraph, I want to know how to arrive at $(2)$ from $(1)$. (It's basically a change of units) : Bethe has derived an expression which...

unit-conversion

Any suggestions?

1000 * 2 / 11.5 is about 174

There's one suggestion.

The problem is with the 7.83 .

@KyleKanos

Are you sure N=rho*N_A/A?

9:12 PM

Take a look at equation 2 here:
http://en.wikipedia.org/wiki/Bethe_formula#The_formula

Then I'm out of ideas. Sorry

Thank you very much for the effort.

@GraceNote, is dimension10's idea feasible? — Emilio Pisanty 2 days ago

I wonder how that managed to ping Grace

@ManishEarth As it's somewhat related to chemistry, what's your suggestion about my question?(above, change of units....)

N is the number of atoms per cm^3.

Then is N=rho*N_A/A correct?

/busy

Brandon Enright

9:26 PM

/iwantapony

3

10:05 PM

@BrandonEnright well I would like to, but some people complain when comments are cleaned up. So we've kind of backed off. At least on this site, we don't usually go around proactively cleaning up comments, we'll just focus on the ones that are flagged.

Brandon Enright

@DavidZ Comments don't usually bother me. I rarely flag them. I haven't seen any reason to complain :-)

Yeah... it mostly becomes an issue when people put information in comments and expect it to stay there permanently

10:26 PM

@BrandonEnright by the way: that is what effective moderating feels like much of the time.

There is little or no positive correlation between popular questions and good questions.

4

(There may actually be a negative correlation.)

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