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There is a question I have regarding profile views as shown on my homepage. If a person views a profile twice then will the homepage mentioned it as two profile views or one ?

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T Abraham

03:28

Hello,

is anybody available to chat?

Gowtham

04:21

maybe :)

Kyle Kanos

I'm here, but barely

T Abraham

05:01

do you want to talk?

Gowtham

whatsup

T Abraham

hi... I am working on a project, I discussed it with @DavidZ ...

I wanted help... are you available?

here's the conversation:

22 hours ago, by T Abraham

can we talk about path integrals?

Gowtham

i probably wont be able to give useful help , am no expert on calculus.

or QFT

T Abraham

what math level are u studying?

Gowtham

05:16

I am in material science , here only because of my interest :)

doing my masters currently

T Abraham

ok...

well... nice talking to you...

Arc676

Anyone up for a conversation on the Doppler Effect with light?

T Abraham

ok...

Arc676

The Doppler Effect makes sense with sound, because if the source moves forward it's physically impacting the medium the waves are moving through. However, light doesn't need a medium. Does this mean that light Doppler shifts are just waves interfering?

T Abraham

grt question... I will try my best at anwsering...

you know... I think that your explanation of Doppler effect is wrong...

Bcos doppler effect is just about frequency.. not bcos it is physically impacting the medium...

quoting wikipedia:

"When the source of the waves is moving toward the observer, each successive wave crest is emitted from a position closer to the observer than the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrival of successive wave crests at the observer is reduced, causing an increase in the frequency. "

the key part is "causing an increase in the frequency"

@Arc676 I hope that helps...

Arc676

05:34

Thanks, I will check that article

In the Wikipedia article it states that the velocity relative to the medium must also be considered with sound. Does this mean that when the wind is traveling in the same direction as the siren the Doppler effect will be reduced?

T Abraham

unfortunately, i am not sure...

however, i think that it doesn't make a difference

@JamalS are you available?

Simha

@Arc676 I think the reason you feel that light undergoing doppler shift without a medium is unintuitive is because you are explicitly comparing a purely longitudnal wave (sound) with a purely transverse one (light). Maybe a more apt comparison would be waves on water..

Gowtham

i think wind only affects the intensity of sound received and not the doppler effect of sound or velocity of sound in the medium, and regarding light you should read wiki articles on Relativistic Doppler effect and General Relativity. I think the only answer i can think of is the red/blue shifts is due to the relative velocity between the source and observer ,

T Abraham

i agree w/ @Gowtham

Arc676

Since sound is a longitudinal wave, where is the amplitude?

The wind could increase the wavelength if it moves in the same direction as the wave but that won't increase intensity

Gowtham

05:48

how does the "wind increase the wavelength if it moves in same direction of wave" happen

Arc676

I'm not entirely sure it could work. In a longitudinal wave, particles vibrate in the same direction as the wave. If the wind is moving in the same direction as the wave as well, it will push the air further so the air particles already moving "forwards" will be pushed further.

T Abraham

that's why I thought it might not be true...

If it did, maybe the world would be very different!

Arc676

?

T Abraham

because changing wavelength of sound, light, etc. could be useful applications...

Simha

@Arc676 In longitudnal waves, the amplitude is part of the wavelength itself, and both are related, unlike in transverse waves where amplitude and wavelegth need not be related at all..

Arc676

06:00

I see. Is there some sort of equation to find the amplitude having the wavelength? With the slinky-style diagram of a longitudinal wave is it possible to label the amplitude?

Gowtham

cosmoquest.org/forum/…

Arc676

Thanks

Gowtham

Look for Clausius's answer in this : physicsforums.com/threads/…

Derek 朕會功夫

07:02

anyone here

Arc676

Yes

Derek 朕會功夫

Can anyone explain a question regarding wavelengths?

Arc676

I can try

T Abraham

me too..

Derek 朕會功夫

So I got an equation here: y(x, t) = (0.002 m) sin((64.8 m^-1)x + (303 s^-1)t)

T Abraham

07:05

what about them...

Derek 朕會功夫

To find the wavelength I do 2pi/k = 2pi/64.8

but then apparently it's not the same as the answer

T Abraham

ok..

Arc676

so what are your value for t

Derek 朕會功夫

Is there something I did wrong that I didn't notice?

t is a variable

T Abraham

@Arc676 how does that matter?

Arc676

07:07

Well if y is a function with parameters x and t you need to define them right? In a 2D graph x is just the x co-ordinate

Or is there something I'm missing?

Derek 朕會功夫

@Arc676 This is a 3d graph, describing a wave moving in time

Arc676

I see

T Abraham

i'm pretty sure it is a mutlivariable fucntion

Derek 朕會功夫

yea

so 2pi/64.8 is the wavelength right??

T Abraham

I think that you have to convert sin into cos.. or does is not make a difference?

Derek 朕會功夫

07:09

sin and cos are just shifting the graph to the right by pi/2

T Abraham

yes..

gota go..

Derek 朕會功夫

so nothing should change

ok

Arc676

Well I tried graphing it

Derek 朕會功夫

how did it go

Arc676

I defined your function as f(x,t)=0.002*sin(64.8x+303t)

then graphed z=f(x,y)

would that be correct for your wave?

Derek 朕會功夫

07:12

yes

I believe 2pi/64.8 is indeed the correct answer, as I see from various source like hyperphysics.phy-astr.gsu.edu/hbase/waves/wavsol.html

I bet it's the answer key that's incorrect

hwlau

@Derek朕會功夫 it is correct

Arc676

just out of curiosity, u realize that graphing z=f(1,y) yields exactly the same result right?

Derek 朕會功夫

@Arc676 what do you mean by that

you shouldn't get the same result since you are now only looking the x=1

just looking at how one particle in the wave moves in time

Arc676

it might be a limitation of my graphing app

Derek 朕會功夫

@hwlau thanks for the conformation

confirmation*

Arc676

07:18

(Tex math doesn't work)

Derek 朕會功夫

man I hate these online problem platforms

@skullpatrol it will do the calculations from left to right so I don't think that's a problem

skullpatrol

I just realized that :)

hwlau

@Derek朕會功夫 what is that platform

Derek 朕會功夫

@hwlau that's smartPhysics, if you are wondering

hwlau

@Arc676 it does somehow work, people need a script for it to work

Arc676

07:26

I see

hwlau

and they use it here often

Arc676

I would assume so. Math is an essential part of physics

hwlau

@Derek朕會功夫 Just send the tutor/instructor an email with screenshot to explain it

Derek 朕會功夫

@hwlau Given that it's already the end of the semester and this is an optional exercise, I don't really have the feeling to report it

:/

hwlau

@Derek朕會功夫 how stupid do you think of the system, or is it just manual error

Derek 朕會功夫

07:35

@hwlau I think overall the system is not bad, especially how you can get instant response, but when you get a wrong answer all you get is a "cross" and you don't know where your mistake is at

hwlau

@Derek朕會功夫 It is how automatic system worked. At best, they will have a sequence of question guiding you with some feedback

If the one who make it is patient to do so

BTW, you name look so strange

Derek 朕會功夫

@hwlau why is that?

hwlau

@Derek朕會功夫 Sound strange

Derek 朕會功夫

@hwlau you mean the chinese text after my name?

hwlau

:19094284 There is a button to upload/ image

@Derek朕會功夫 yup

Derek 朕會功夫

07:41

@hwlau I just put that there cause it sounds funny :)

It doesn't really make any sense

hwlau

@Derek朕會功夫 it does make some sense, but strange "Derek I know kungfu"

Derek 朕會功夫

@hwlau Looks like you know chinese too

hwlau

@Derek朕會功夫 yes

usually you will only find it strange if they know it

except the shape

Derek 朕會功夫

@hwlau Actually I know chinese too, if you take a look at my location in the profile

hwlau

@Derek朕會功夫 me from HK too

Arc676

07:47

@Derek朕會功夫 That's clever

Derek 朕會功夫

@hwlau Seems like I guessed it right, by looking at your last name

@Arc676 What is clever?

Arc676

The Chinese bit. Especially how its not the most commonly used characters for the meaning you want to express

The first 2 are traditional chinese aren't they?

Derek 朕會功夫

@Arc676 They are

Arc676

:)

Derek 朕會功夫

But 朕 actually has more meaning than just "I"

hwlau

07:51

@Derek朕會功夫 are you us or hk people or you just stay there?

Derek 朕會功夫

@hwlau from hk but moved to us quite a long time ago

hwlau

@Derek朕會功夫 clever move

and you have lots of rep at SO

I do think US is better for programming jobs

Derek 朕會功夫

@hwlau especially in mountain view

hwlau

@Derek朕會功夫 where are you living, seattle?

Derek 朕會功夫

@hwlau no

hwlau

07:57

Nevermind

Derek 朕會功夫

@hwlau chicago

a great city

Gowtham

heard it has been really cold this winter , is it ?

hwlau

@Derek朕會功夫 how great is it?

Derek 朕會功夫

@Gowtham kind of windy like usual

@hwlau It has a great skyline

and people are great there

hwlau

ic, is it snowy in the winter?

Derek 朕會功夫

08:02

oh yea it snows every year

Gowtham

very snowy and "wind-chilly" too , hehe

hwlau

@Derek朕會功夫 so you can ski there? Is the lake frozen in the winter

Derek 朕會功夫

@hwlau unfortunately there aren't that many place for skiing because there's no hills or mountains in the city, and the lake Michigan isn't frozen either

small lakes are frozen, but I won't walk on them :)

hwlau

Sound nice

So it is not as cold as Canada

and you do a lot of thing out there

Derek 朕會功夫

@hwlau like what?

hwlau

08:09

@Derek朕會功夫 Nevermind. Are there lots of thick snow on the road or not

Gowtham

usually its cleared by local authority i think , but off the road you can see 2 or 3 feet snow or even more depending on the weather

hwlau

@Gowtham you live in chicago too? 2 or 3 feet is quite a lot

Derek 朕會功夫

The city government will clear the road for us, but the dirty snow are all shoved onto the side walk which piles up quite high

Gowtham

2 or 3 feet seems normal , i lived at state college pennsylvania ,chicago and my place can be comparable for snow received i guess,

but chicago is far colder due to windchill effect

hwlau

I would think that the snow is less in the middel part of US because there are not much sea water there

Derek 朕會功夫

08:16

@hwlau you forgot the lake

hwlau

ok

Derek 朕會功夫

see you guys

gotta leave now

hwlau

see you

Derek 朕會功夫

@hwlau you might also want to join our group here if you want :)

hwlau

@Derek朕會功夫 thx, I will take a look

Huy

10:11

Why the invite, @skullpatrol?

skullpatrol

I'm sorry I am on mobile and I hit the wrong button @Huy

Huy

@skullpatrol: And I was already hoping you liked me. =(

skullpatrol

I do pal :D

You're cool @Huy

Please accept my apologies.

Huy

Fine.

Danu

11:30

So I recently started a petition to have a second course in GR in my degree, and it turns out there is quite a lot of interest. However, now that the plan has become quite feasible, I'll have to actually come up with what kind of topics I'd be interested in learning about

This has proven to be quite a difficult question. In my degree, there is only one course on GR, but there are courses on 1) Cosmology 2) QFT in curved spacetime 3) "Black holes and instantons" (?)

...so any proposed course should not have too much overlap with any of those pre-existing courses.

ACuriousMind

@Danu: So, uh, what did you have in mind when you started that petition?

Danu

like.... "more advanced GR"

Turns out it's really not obvious what that is.

ACuriousMind

The three courses you just cited sound to me like they are exactly that

Danu

I was thinking of stuff like... (note that I only know these words, not their actual content) ADM formalism, conformal diagrams, maybe singularity theorems...

I also saw this interesting book by Penrose & Rindler on Spinors in curved spacetime

Huy

That's no good.

Danu

11:34

What isn't? :P

Huy

The book.

Danu

Penrose & Rindler? What do you dislike about it?

oh, oh yeah... also Cartan formalism!! @JamalS

ACuriousMind

Do you already treat GR mathematically by looking at frame bundles, jet bundles, and stuff? If not, I'd say that would be quite fitting for a mathematical physics degree, too

Danu

^nope, do you have a reference book?

Our GR course is extremely physical

...it's taught by Prof. Mukhanov! ;D

Huy

@Danu: Did you use a textbook in your GR course?

ACuriousMind

11:39

@Danu Not really, but the reference list, for example, on the Wiki article for covariant field theory looks like a starting point

Danu

@Huy Not really... Mukhanov seems to freestyle. But take Carroll's book as an approximate equivalent to get some idea

(without the final chapter on QFT in curved spacetime, of course - Mukhanov will teach from his own book for that haha)

Huy

I've heard good about Carroll's book.

Danu

Very good book - I read it about 1.5 years ago as an undergraduate and was able to understand almost everything :)

ACuriousMind

@Danu I had not heard of him before, but it seems you've got quite a famous lecturer there

Danu

He is one of the fathers of inflation, yes :)

And he's epic

Huy

11:41

@Danu: Our GR course followed Dirac's and Pauli's book. It was rather mathematical, too.

Danu

@ACuriousMind Just check this out youtube.com/watch?v=S06-xP4jK6g

ACuriousMind

We followed Schutz. Ugh.

Danu

Lmao

unfortunate

ACuriousMind

Could his Russian accent be more cliche? :D

Danu

@Huy Do you mean Dirac's 'General theory of relativity' or something else?

@ACuriousMind viekter

(vector)

Huy

11:42

@Danu: Yes. That.

Danu

@Huy That seems like literally the worst book to learn GR from as a physicist. 2 pages on the Schwarzschild solution?!

Huy

@Danu: I'm a mathematician. :P

Danu

Yeah... then there's not really any need for 'useful' things ;)

But that does make you a good reference. Any tips on which topics one might want to look into?

Huy

@Danu: It was a course for physicists though.

@Danu: What have you seen already?

Danu

@Huy Carroll minus the appendices

Very little mathematical formalism - quite a lot of physics

...but I'm not interested in purely mathematical things to do - just more advanced things which may (or may not) require more advanced mathematics than basic GR

Huy

11:46

@Danu: Do you mean Spacetime & Geometry or Lecture Notes on GR?

Danu

@Huy The book (although the notes probably cover almost the same material)

Huy

@Danu: Oh, I've never seen the book before. Just a lot of friends telling me the lecture notes are really outstanding.

Danu

The book is an extension/completion of the notes.

Anonymous

@Huy You study Physics?

Huy

@Ashwin: No, technically, mathematics.

Danu

11:48

@ACuriousMind your recommendation about the bundles etc seem a little too superfluously mathematical to me (I don't mind mathematics, but don't want to organize a course on GR just for the sake of mathematics)

ACuriousMind

@Danu Yeah, right as I read your last comment, I thought it might not be what you want to do

Danu

It's also intended for some non-math.phys. students

Anonymous

@Huy Why is that most Thermodynamics books do not cover mass transfer and things?

ACuriousMind

I find it interesting because it shows the similarity to gauge theories, and thus other forces, but it is really not needed for anything physical

Huy

@Ashwin: I don't know, I haven't studied Thermodynamics.

ACuriousMind

11:50

@Ashwin In the grand canonical ensemble, particle number is not constant, and particle transfer is mass transfer, no?

Danu

@KyleKanos Please don't solve this user's homework for him/her (I had quite a long talk before, and it became clear he/she is really missing a lot of basic knowledge of ODE's)

Anonymous

@ACuriousMind Actually not much of Thermodynamics I have done.

Danu

@Huy So, do you have any ideas about what could be interesting?

ACuriousMind

Then "most thermodynamics does not cover mass transfer" is a bold statement ;)

As I understand it, the grand canonical ensemble does/is able to do precisely that.

Huy

@Danu: I can't think of anything off the top of my head, but I'll let you know if something comes to mind.

Anonymous

11:52

Actually I am doing Engineering and my thermodynimics book (Blundell) does not cover it!

Anonymous

Does the one by Greiner have it?

ACuriousMind

::shrugs:: I don't know many books

Especially not on thermodynamics, I rather dislike that subject

(which may just be due to the abysmal courses I had on it)

Simha

12:06

Merry winter bash everyone ! :D

Huy

12:22

Did any of you guys use the feynmf package before to create Feynman diagrams? I have troubles using it.

Danu

Yes

I learned how to do it last week - it's all fresh! :P

I'm using feynmp though

(slightly different command in cmd.exe)

Huy

@Danu: Are you on Windows?

Danu

Yes

Huy

@Danu: I'm using TeXnic Center with MikTeX. I just included the package feynmf and tried the code I found here: de.sharelatex.com/learn/Feynman_diagrams However, I get an error of the form "I can't find file 'diagram' <*> \mode:=cx;nonstopmode;input diagram".

Danu

it's pretty complicated

Huy

12:27

Can you guide me through it?

Danu

so you put that in - that's okay

then you run Latex -> DviPS -> PS2PDF

one time

it should not give errors

then you have to go to the command prompt (strange, I know)

Huy

I don't have that option, I only have LaTeX -> DVI -> PDF.

No postscript.

Danu

ehm... you should be able to change it

there's usually compile options

Huy

In the dropdown menu, where currently LaTeX => PDF selected, I don't have PS, anywhere.

The nearest option to the one you said is LaTeX -> DVI -> PDF

Danu

For this one usually has to go to the settings

there, hopefully, you'll find it

Huy

12:32

No, but I could add it.

These are all available profiles.

Danu

Hmm, okay. I'm not an expert but my friend who taught me to use feynmp always said to use the full chain

Also, other editors do have this as a standard option most of the time

e.g. TeXMaker, TeXStudio

Huy

It apparently isn't, but I'm trying this: tex.stackexchange.com/questions/58729/latex-dvips-ps2pdf @Danu. I'll tell you if it works then.

Simha

Hi guys, since many of you here are active researchers and theorists, I wanted to get an insiders view as to the recognition scientists get for the work they do.

People tell me the pay scale is miserable and the recognition too. I tell them that as long as my passion for physics keeps burning, I'm okay to put up with it.

Then they tell me that I won't understand some things until I start earning. So I wanted to get an insider's view as to whether this is actually true or not..

And btw, Merry Winter bash everyone !

Danu

I'm not a professional physicist (yet), but you defiinitely shouldn't be in this for the money.

The effort-to-economic payoff ratio is very high

...but you do get the bragging rights (in certain circles, at least)

Huy

@Danu: I get the same error if I run Latex -> DviPS -> PS2PDF

Danu

12:42

@Huy Okay.

Well, let's just proceed with my method

maybe it'll work

Now, you go to the command prompt

are you familiar with how to use it?

Huy

@Danu: I think so.

Danu

Okay. Go to the folder that your files are in

(go to as in inside the command prompt)

Huy

ok

Danu

actually, you can also check the actual folder: is there another file in there with the name of your diagram?

Huy

yes

Danu

12:45

Good

Huy

there is diagram.mf and diagram.mp

Danu

Ok, now that you're in your folder in the command prompt

run: mpost diagram

Simha

@Danu I've heard it's a popular fact among researchers that these days since research work is carried out by large organisations, induvidual effort is no longer valued as in the earlier days..

Danu

(or other name if you renamed the diagram)

Huy

@Danu: Done.

Danu

12:46

does it give you some sensible-looking messages?

Huy

yea

Danu

k

Huy

metapost did something

Danu

now go back to your latex

Huy

and 1 output file was written

Danu

12:46

and run the full chain

good, that sounds perfect

should work now

Huy

still the same error

Danu

ah crap

Huy

+1

Danu

is there a .log file in your folder now?

Huy

yes, for both the diagram as well as the .tex file

Danu

12:47

yeah, okay

the one for the diagram is the one you need

I'm honestly not enough of an expert on latex to help you out much more than this... It's something with your LaTeX

some setting probably has to be adjusted...

to get this chain to work properly

Huy

@Danu: This is MetaPost, version 1.803 (MiKTeX 2.9 64-bit) 16 DEC 2014 13:46
**diagram
(mpost.mp (D:/Program Files (x86)/MiKTeX/metapost/base/plain.mp
Preloading the plain mem file, version 1.004) )
(C:/Users/***/2nd derivative/diagram.mp
(D:/Program Files (x86)/MiKTeX/metapost/feynmf/feynmp.mp) [1] )

Here is how much of MetaPost's memory you used:
301 strings using 4436 characters
1534584 bytes of node memory
922 symbolic tokens
14i,77n,28p,105b,3f stack positions out of 16i,96n,32p,200b,4f
1 output file written: diagram.1

Danu

But at least this is the general idea

@Huy Yeah, this is how it should be

Huy

I'll try rebooting. Works wonders sometimes.

Danu

Latex -> cmd.exe mpost [name] -> Latex

good luck

Huy

Nope, still exactly the same error message. @Danu

Danu

12:54

I'd suggest goin to the TeX chat - they're pretty helpful

Sorry I wasn't able to solve your problem!

Simha

13:10

@Danu I see you specialize in mathematical physics and are also pretty active as a science historian. I wanted your views as to whether the origin of math as a tool in physics was purely accidental or not.

I've heard many such an argument. I don't find it to be true, however, since math is clearly the most efficient way of dealing with science since time immemorial..

But when did scientists exactly begin to realise it ? Was it after the emergence of calculus, or much before it ?

Kyle Kanos

13:32

@Danu It definitely seemed like he/she was missing a lot of basic knowledge of calculus really

Kyle Kanos

14:07

@Simha Well, there was Zeno's paradoxes that required a bit of math (e.g., halving distances) to describe something physical (Aristotle's rebuttals also show signs of calculus).

AnjumSKhan

Consider a 10000 kg weighing body is placed on a weak small table. Naturally the table will break and the body will accelerate through it. In that case for the body we can write mg-N = ma , where a is accel of the body. And thus we can find the normal force N by table on the body .

Jim

@AnjumSKhan what was this in response to?

ACuriousMind

@Simha The Unreasonable Effectiveness of Mathematics in the Natural Sciences

"However, it is important to point out that the mathematical formulation of the physicist's often crude experience leads in an uncanny number of cases to an amazingly accurate description of a large class of phenomena. This shows that the mathematical language has more to commend it than being the only language which we can speak; it shows that it is, in a very real sense, the correct language."

AnjumSKhan

@Jim I asked a question in the forum and now I am asking my doubt here.

@Jim It is related to Newton's 3rd law.

ACuriousMind

@AnjumSKhan We ain't a forum. Also, I don't understand your question

Kyle Kanos

14:17

Your question was answered though?

AnjumSKhan

@ACuriousMind We say the table exerts a forceequal and opposite to that applied by book on the table and so book remains at rest.

@ACuriousMind I was wondering then , why a massive book will break through the table.

ACuriousMind

@AnjumSKhan Because the table cannot withstand so strong a force?

Kyle Kanos

@AnjumSKhan Obviously the answer is the force due to the book is greater than the force the table can withstand

AnjumSKhan

@ACuriousMind thats what I am asking, then where is the 3rd law ?

Kyle Kanos

Newton's laws say that forces in equlibrium are equal and opposite and produce no net acceleration

The breaking table is not in equilibrium with the book

Gowtham

14:20

@AnjumSKhan when it falls there wont be any normal force if thats what you are asking
it is "free fall" once the table breaks

Jim

when the table breaks, the book is not exerting its entire weight on the table. only enough force to make the table accelerate with the book is applied and that is reacted upon the book. But it does not cancel the weight of the book, so both table and book fall

AnjumSKhan

@Gowtham So normal reaction on the Book by the table can be found using mg-N=ma ?

Jim

if the table is massless, yes

AnjumSKhan

@Gowtham m = mass of book, a = accel of book after breaking the table

Gowtham

when the table breaks there is no "normal" i think . and the book has a=g

Jim

14:22

when the table breaks, a is not g

AnjumSKhan

But still when we keep a book on table, so N must be there ?

Jim

the acceleration of the book is less than g because some of the force is used to complete the breaking of the table. Once the table is fully free to fall, then the table and the book will have acceleration of g.

Gowtham

depends on how slow or fast you actually place it on the table i think , when the force exerted by the book on the table reaches the critical or breaking point the table is gonna break and book is gonna fall through . but once the table breaks and when there is no contact b/w book and table, there is no normal and the book should be in free fall

AnjumSKhan

Then how 3rd law is acting here in the entire scenario ?

Jim

If I had a video camera and silly putty, I could make such a demonstration to explain this. The point is, the table will only provide as much normal force as it can withstand. Any additional force applied makes it move. The book will make the table move with it, but it will not apply the entirety of its weight to do so. Only as much force as is required to make the table move with it is applied to the table. This force is opposed by the table, which slows the book's acceleration.

The excess force is not applied to the table and is used to make the book accelerate through the table

AnjumSKhan

14:34

@Jim lot of confusion, will do more reasearch on this. thankx.

Gowtham

@AnjumSKhan as Kyle Kanos said when two bodies are in EQULIBRIUM , then newton laws are valid. So till the breaking point its valid . after that if the configuration of the table is awkwardly such that it can maybe hold the book then we can talk about normal forces. but if it breaks in my knowledge the book should just be free falling without at g

Danu

@KyleKanos Yeah... and didn't seem willing to learn to do some basic stuff before jumping into more difficult matters... an all-too-common problems, especially amongst those who haven't been studying all that long yet :P

@Simha Purely accidental? What do you even mean by that

Jim

@Gowtham Newton's laws are always valid in classical problems. Not just equilibrium. They are easier to see in equilibrium, but in every case an applied force is still opposed by a force of equal magnitude. In non-equilibrium cases one must remember that the entire force on one object is not fully applied to the other

ACuriousMind

@Danu There are people who believe (or pretend to believe) that science and math are not intrinsically connected - that it is a mere historical accident that today's science is so heavily relying on mathematics

Danu

@ACuriousMind I'd venture to guess that these are not mathematicians... nor physicists or otherwise mathematically educated scientists

ACuriousMind

14:39

You're not wrong

Kyle Kanos

I'm reading the AMS paper (finally) and the following made me laugh: Figure 4 shows the behavior of the positron fraction at low energies, from 1 to 35 GeV.

A few GeV is "low energy."

Gowtham

@Jim ok my statement was wrong. All i can say to @AnjumSKhan when there is action there is equal and opposite reaction . When the table breaks, the action i.e the weight of the body wont act on the table anymore. so there is no reaction . i dont know how to explain in a more simple way .Sorry

Danu

@KyleKanos Of course, on cosmological scales! :D

Gowtham

If the sub-site like chemistry.SE is in beta , does that mean not much moderating is done ? all i am seeing is lots and lots of homework type problems O.o

ACuriousMind

@Gowtham Are homework type problems even off-topic there?

Gowtham

14:48

well its not mostly off-topic but blatantly and openly asking for direct solutions without any prior attempt

For Eg : chemistry.stackexchange.com/questions/21787/…

he is asking for equations :D like sometimes i think people dont even use google and just blindly use the site like an answering machine :P

ACuriousMind

It seems that the moderators/3k users are lazy, then :P

Danu

@Gowtham History of Science and Math is in beta, and I am one of its moderators. I certainly try to maintain high standards (though homework is not really a problem on HSM)

Gowtham

@Danu ok. when i first visited this site i was also clueless but still somone posted that common thing about the site

this "Hi and welcome to the site! Since this is a site that encourages learning, you will get much more help if you show us what you have already done. Could you edit your question with your thoughts and ideas?" and i tried to do solve first and only post after that :)

@ACuriousMind i noticed yesterday you were discussing dota 2 with one of the users , you like the game ?

Simha

@KyleKanos Good point. I was thinking science's real breakthrough was clearly Newton's era, which saw the emergence of calculus, and thus it resonates with the fact that math is indispensable to physics.

Jim

@Gowtham Physics.SE tends to be stricter than most about homework-like problems. If we didn't do that, we'd become AppliedMath.SE

ACuriousMind

14:57

@Gowtham I played DotA years ago, and @Phonon is trying to get me to come back and play DotA2, but I haven't played it yet.

@Jim ::shudder::

Though, physics is "just" applied math, of course ;) (I won't link the infamous xkcd again)

Jim

@ACuriousMind sixteen times is probably enough

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