The h Bar

7:00 AM

@MAFIA36790 Very good.

It's just that one should not do a calculation until the answer is already known :)

user116211

@DanielSank the other post showed if the potential energy $U$ is time-dependent; then the sum of KE and PE is not constant but equals to $\dfrac{\partial U}{\partial t}~\mathrm dt$....

DanielSank

Yes.

So what is the issue?

user116211

But here, in my case, it has been told that the time-derivative of the work-function $U$ has to be zero.

DanielSank

Ohhhhhh

What's "work function" again?

user116211

@DanielSank ;P

user116211

7:02 AM

Wait...

user116211

user116211

Is the visibility right @DanielSank?

Secret

1

Q: Uncertainty principle in macroscopic world

Disclaimer: I am not an expert in quantum mechanics. Uncertainty principle says $\Delta x\Delta p\geq \frac{\hbar}{2}$. I recall having read somewhere that Heisenberg arrived at this result considering interaction of photon with an electron, which implied an in-principle limitation on our measur...

23

Q: Isn't the uncertainty principle just non-fundamental limitations in our current technology that could be removed in a more advanced civilization?

From what I understand, the uncertainty principle states that there is a fundamental natural limit to how accurately we can measure velocity and momentum at the same time. It's not a limit on equipment but just a natural phenomenon. However, isn't this just an observational limit? There is a def...

quantum-mechanics measurement-problem uncertainty-principle observers

If such a thing has not been observed in macroscopic world, doesn't this imply that uncertainty principle is a matter of measurement limitations?

>This sentence screwed and diverted the attention of the question (too bad this is actually the main question..., which is why they said it is an exact duplicate)

THIS is the interesting question:

> But if one accepts this, then it means that in-principle one could make as precise measurements as one wishes. And as as either ΔxΔx or ΔpΔp is made smaller without bounds, the other will rise without bounds, and at some point must be capable of observation in the macroscopic world, no matter how small ℏℏ is.

DanielSank

@MAFIA36790 The visibility is fine.

user116211

@Secret Must have copied it from somewhere ;P

Secret

7:06 AM

Anythign after the arrows

user116211

@Secret Give a space after >

Secret

Always have to race against that stupid edit clock to post messages

user116211

@Secret :(

user116211

@DanielSank: Could I make my argument clear to you?

Secret

I have to do so because ACM cannot in general see that line break messages are actually related, thus I am trying to remove all those linebreaks while keeping the message short

user116211

7:08 AM

@Secret ohh.

Secret

I also need to ensure my messages won't span across many posts, because that is one reason why they are confusing

which is why I use this placeholder approach

DanielSank

@MAFIA36790 The problem is that in multi-line posts, the formatting doesn't work.

user116211

@DanielSank oh.

DanielSank

@MAFIA36790 I think I understand what you're asking but I'm not 100% sure.

user116211

@DanielSank ohh... okay.

DanielSank

7:10 AM

@MAFIA36790, could you perhaps write what is your question in a concise way?

I think you want to say this:

Secret

Some time later, I need to think carefully how the cannonball example can still obey the uncertainty principle... but before then I will need to finish my topology reading first...

DanielSank

1) I understand that if U depends on t, then the energy is not conserved.
2) There is a book that defines the "work function" as a certain combination of U and its derivatives with respect to the velocities.
3) The book says that if the work function depends on t, then the energy is not conserved.
4) How are #1 and #3 related?

Is that an accurate representation of your thoughts?

user116211

@DanielSank Don't take the 2 now; in that case $U$ depends on the velocities $\dot q_i$ but not explicitly on time $t\,.$

DanielSank

Edited

user116211

@DanielSank Hmm; you have exactly wrote what I'm asking.

DanielSank

7:14 AM

Good!

Ok, well, I think in most cases it would not even be considered that $U$ could depend on the velocities.

user116211

@DanielSank But 2) is irrelevant here.

Secret

Hypothesis of the Principle of least resistance for question: Given a question that has multiple subquestions embedded, usually only the easiest and perceived to be most important question will be answered. Mark as duplicate seemed to be function on such levels, as clearly some subquestions are never answered, which is why when questions are closed, the OP tend to complain that it is not a duplicate

user116211

@DanielSank okay.

DanielSank

@MAFIA36790 But #3 requires #2!

@Secret Asking more than one question at a time should be very clearly stated in our guidelines to be a very bad idea.

As you have just noted, posts with multiple questions are full of potential for problems.

user116211

@DanielSank Hmm; as I said; 2) talks about $U$ which depends on velocities but not explicitly on time $t\,.$

DanielSank

7:16 AM

@MAFIA36790 #2 defines "work function".

Without that, #3 is nonsense.

user116211

1) and 3) are talking about $U$ which only depends explicitly on time.

DanielSank

:|

$\text{work function} \neq U$, right?

Secret

Well it's actually more complicated than that. Most question has some kind of chain structure $A \rightarrow B \rightarrow C \rightarrow \cdots$ (to be elaborated, I cannot type fast enough)

user116211

@DanielSank no; it defines $V$ with respect to $U $ such that the sum of PE and KE remains the same when $U:= U(q_i,\ldots, q_n;\dot q_1,\ldots, \dot q_n)\,.$

DanielSank

@MAFIA36790 What's $V$?

user116211

7:18 AM

The case is scleronomic.

user116211

@DanielSank potential energy.

DanielSank

@MAFIA36790 Oh jeez. What's $U$?

user116211

@DanielSank ;P Work function.

DanielSank

@MAFIA36790 OH!

Could you do me a favor?

user116211

Wait.... let me jot down this...

DanielSank

7:19 AM

Please write the definition of $V$.

user116211

clearly....

DanielSank

I mean $U$.

user116211

@DanielSank I'm doing that ;)

user116211

So, $\overline{\mathrm dw}$ is not always integrable; when it is integrable, it can be expressed as the differential of a certain function. This function is the work-function $U\,.$

DanielSank

k

Secret

7:20 AM

where the main question (let's call it #) is preceeded by a chain of reasoning of the OP and the sources he/she found. Since the individual elements $A,B$ that form part of the chain of reasoning are the OP's guess, they are technically speaking, subquestions (because it is not 100% known to be true). This is why when

user116211

That is, $\overline{\mathrm dw} = \mathrm dU\,.$

user116211

Now, the generalised forces can be expressed in terms of the work function as: $$F_i = \frac{\partial U}{\partial q_i}\,.$$

user116211

Till now, okay @Daniel?

Secret

answering questions that has such structure in general, one is effectively answering multiple related questions at once in order. The OP will only be satisfied with the answer only if a key part of the chain of reasoning is addressed

DanielSank

Dude, I don't know what $\overline{dw}$ is.

user116211

7:22 AM

@DanielSank It's the infinitesimal work.

DanielSank

@MAFIA36790 What does that mean?

user116211

@DanielSank okay....

DanielSank

No, I'm serious.

user116211

@DanielSank I'm writing....

Secret

Suppose for poetic reason we call answering a question "killing a question". In order to kill a question, in general you cannot just chop off the head #, you need to chop off starting from the earliest points where the whole chain of reasoning that lead to the question. In other words, answering a question is a hard business because you cannot kill it without killing the entire chain in the most general case. This is where the idea of multiple subquestions came in (Addressing

the chain of reasoning is also part of the question)

user116211

7:25 AM

@DanielSank: $\overline{dw}$ is the infinitesimal work which is defined as $$\overline{\mathrm dw}= F_1~\mathrm dq_1 + \ldots + F_n~\mathrm dq_n$$ where $F_i$ is the force and $\mathrm dq_i$ is the infinitesimal displacement.

DanielSank

@Secret Yeah consider a question that says "I read A, so then it must be B, so I ask, why C?"

user116211

Could I make it clear @DanielSank?

DanielSank

If it turns out that A does not imply B, then this should be stated in the comments, and nobody should answer.

It would be appropriate to vote to close because this question presupposes a false premise.

Or, perhaps, edit the question to ask "Why does A not imply B?", but this will only work some times.

@MAFIA36790 Now we're getting somewhere.

Secret

Yes, then addressing why B is invalid will kill the question, but most people overlook that and go for killing C (because C is easier to kill or already have examples how to kill them), but OP is not satisfied because B is not killed thus logically should lead to C, so to OP, C is still alive

user116211

The present practice is to use the negative of work function to define the forces i.e, $V= -~U$ and $$F_i = -~ \frac{\partial V }{\partial q_i}\,.$$ Here, $V$ is called the potential energy.

DanielSank

7:29 AM

@Secret Yes, this is a mistake on the part of whoever wrote the answer. I don't mean that as an insult. It's an easy mistake to make.

@MAFIA36790 Wait, you jumped suddenly to "work function".

@MAFIA36790 would it be easier for you to post this as a question so I can read the whole thing all in one place without the broken structure of the chat?

user116211

10 mins ago, by MAFIA36790

So, $\overline{\mathrm dw}$ is not always integrable; when it is integrable, it can be expressed as the differential of a certain function. This function is the work-function $U\,.$

Secret

There are a lot of questions (e.g. mine are full of these) that the whole chain of reasoning will broke down because of a false premise. These questions should be VtC plus a comment stating what the false premise is (and optionally, what the correct premise should be if there is one) Alternately, when answering them, one should address that there is a false premise and how the question is invalid, and (if there exists a correct version of it), one can state what should be thought instead

user116211

@DanielSank But this would be then totally a homework query; that would be immediately closed. The question would be like How to proceed from this point to prove that for time-dependent $U,$ law of conservation of energy doesn't satisfy? And the reply would be Where is the effort? That's it.

DanielSank

@MAFIA36790 Now way. You can definitely ask this well.

Secret

I noticed most answerers are ok at noticing false premise and addressing them, but it is not good enough

user116211

7:34 AM

But @DanielSank, did you get the work function now?

Secret

For example, take a look at some of Johnrennie's and Lubo's answers in most questions, they can often point out where the reasoning of the OP gone wrong and what they should be thought instead

DanielSank

@MAFIA36790 Sort of, dude, but it's hard to keep track of stuff.

I don't have the book in front of me etc. etc.

user116211

@DanielSank okay.

Secret

which is why I guess their answers are often highly voted and accepted (another reason might be because their answers are detailed and to the point)

user116211

Then , I would post this as a question.... I'm really desperate to know this @DanielSank.

Secret

7:36 AM

(Warning, long post will be followed, please be aware)
Now back to the example of the "Uncertainty principle in macroscopic world [duplicate]" question. (At least to me, this question can be analysed as follows):

user116211

@Secret Warning not required, we are accustomed to that ;P

Secret

Line by line analysis begins...

QUOTE=Disclaimer: I am not an expert in quantum mechanics.
-> A Polite statement, generally does not carry useful information regarding the structure of the question

DanielSank

@Secret Yes, I typically remove such phrases and in the edit box I put "remove irrelevance".

Secret

QUOTE=Uncertainty principle says ΔxΔp≥ℏ2ΔxΔp≥ℏ2. I recall having read somewhere that Heisenberg arrived at this result considering interaction of photon with an electron, which implied an in-principle limitation on our measurement capability.
->This setence actually has two parts. Let's break it down as follows:

QUOTE=Uncertainty principle says ΔxΔp≥ℏ2ΔxΔp≥ℏ2. I recall having read somewhere that Heisenberg arrived at this result considering interaction of photon with an electron
-> This is some background reading and known model, Call this A

DanielSank

Yes yes, there are two statements.

The first one is background and is fine.

The second is a completely false statement which does not follow from the first.

Secret

7:41 AM

Slow down, we will get to address the truth value of the statements and their connections soon

QUOTE=, which implied an in-principle limitation on our measurement capability.
-> This is the OP's reasoning. Call this B. Now we have the chain fragment $A\implies B$

Note here I am not evaluating the truth statement of the logic yet

Now

QUOTE=Later this view was rejected and uncertainty principle came to be viewed as a fundamental fact of nature herself, and the principle had nothing to do with measurement limitations. If such an uncertainty does not show itself in macroscopic world, it was explained, it is because of the smallness of ℏℏ.
-> This is some other background reading. Call this $C$, $C$ says $A\implies B$ is false

QUOTE=But if one accepts this, then it means that in-principle one could make as precise measurements as one wishes. And as as either ΔxΔx or ΔpΔp is made smaller without bounds, the other will rise without bounds, and at some point must be capable of observation in the macroscopic world, no matter how small ℏℏ is.
-> This is another of OP's reasoning to defend why $A\implies B$ must be true. Call this $D$

QUOTE=If such a thing has not been observed in macroscopic world, doesn't this imply that uncertainty principle is a matter of measurement limitations?
->This sentence has two parts, let's split it up

If such a thing has not been observed in macroscopic world
-> This is one of the subquestions (without actually being one) in the chain. It is asking whethere $D$ is true

QUOTE=doesn't this imply that uncertainty principle is a matter of measurement limitations?
-> This is based on the OP's logic chain that if $D$ is true, then $A\implies B$ is true, then $B$ is true.

DanielSank

yes.

Secret

Summarising the above we have the following structure of the question:

DanielSank

@Secret I find this interesting!

I apologize for my hasty reaction!

user116211

@DanielSank, It's worthy to let you show this quote of Lanczos:

user116211

> The really fundamental quantity of analytical mechanics is not potential energy but work function, although the physicist and engineer are more familiar with the former concept.

DanielSank

7:51 AM

@MAFIA36790 Yes I think this makes sense to me.

user116211

@DanielSank :)

Secret

$$A \implies B$$
$$\exists C : A \implies B \text{ is false}$$
$$\text{Question:} \exists D : D\text{ true }\rightarrow A \implies B \text{ is true} \rightarrow B \text{ true }$$

user116211

@Secret \exists

DanielSank

@Secret what does the backwards E mean?

Secret

there exists

user116211

7:52 AM

@DanielSank It's a universal quantifier.

DanielSank

I don't understand the third line.

Here's my understanding of what @Secret's post means:

1. A implies B.
2. There's a proposition C, which ways that A does not imply B.
3. ???

Secret

3. There's a proposition D such that if A is true then B is true

Therefore even if the truth value of B is the actual question presented, in order to kill the question, we must address D. Now the comment section actually has evidence to support this conclusion:

DanielSank

What the hell?

What does the first line mean :P

Secret

Given the proposition "$A\implies B$" (I.e. I treat $A\implies B$ as one object)

Bernard Meurer

@DanielSank You're still up dood?

DanielSank

7:57 AM

@BernardMeurer dood

Bernard Meurer

I'm in my lab class already lol

DanielSank

Ohhhh, @Secret I think I understand the notation now.

So we could say this:

$$X: A \rightarrow B$$

$$C: \text{not} X$$

@Secret is that correct for the first two lines?

Secret

put $\exists$ before the C, as we only need at least one C for it to hold

but otherwise, yes

DanielSank

Hahaha I'm confused.

:P

Secret

$\exists$ means "there exists"
Now the 3rd line will be
$$\exists D : X ?$$

DanielSank

8:04 AM

Why do we need the second line?

Or is the point just that it exists in the question?

Secret

the question mark (not sure how it will be done in the correct syntax of mathematical logic) indicates this is asking the truth value of this

Well I am listing out all the stuff relevant to the question, We don't actually need the 2nd line to kill this question

DanielSank

@Secret I don't understand this.

Can you say it in English?

Secret

"Is there exists a D such that X" where X is "if A then B"
Or you want me to fully expand the A,B,X also?

DanielSank

@Secret I guess I sort of get it.

$$A: \text{the uncertainty relation}$$

Right?

Secret

When I post what the comments said, it will become a lot clearer

Yes,
and $$\text{ B : Technical limitation in measurement devices}$$

DanielSank

8:10 AM

I think it's more that:

Actually yeah ok.

@Secret could you link the original post again?

Secret

1

Q: Uncertainty principle in macroscopic world

Disclaimer: I am not an expert in quantum mechanics. Uncertainty principle says $\Delta x\Delta p\geq \frac{\hbar}{2}$. I recall having read somewhere that Heisenberg arrived at this result considering interaction of photon with an electron, which implied an in-principle limitation on our measur...

quantum-mechanics uncertainty-principle

DanielSank

$$X: A \rightarrow B$$

$$C: X \text{ is false}$$

@Secret am I getting it right?

Secret

yes

DanielSank

Ah, very good!

Then the OP says "If $C$, then not $B$".

Right, @Secret?

Secret

yes

DanielSank

8:14 AM

Ah yes, this is all rather clear now.

$$D: \text{If }C\text{ then not }B$$

Then OP says "If $D$, we should be able to see $\Delta x$ or $\Delta p$ coming from $A$ by making very precise measurements.

Secret

and when one is very small, the other will be so large that it should be macroscopic (and can been seen). He then said if this phenomenon is never seen, then would that means B is true

DanielSank

@ACuriousMind @JohnRennie I have absolutely no idea why you guys closed this question as a duplicate.

Secret

Now the evidences to support my reasonings:

John Rennie

@DanielSank The question asks: If such a thing has not been observed in macroscopic world, doesn't this imply that uncertainty principle is a matter of measurement limitations?

The duplicate answers that question

DanielSank

@JohnRennie That is an absurdly reductionist view of the question as a whole.

Secret

8:19 AM

->Qmech have addressed that "X is false" is true, but have said nothing about $D$

DanielSank

OP has added an interesting consideration: If we can measure as finitely as we want, then we should be able to see huge quantum fluctuations in one operator by measuring the other.

Secret

@Qmechanic Thank you for the link. It doesn't answer my question though. — Zero 24 hours ago

-> Hence the OP's response as D is unaddressed

DanielSank

Yes, @Secret I mostly see the situation now.

The close votes are misplaced, in my opinion.

Secret

Let me post the remaining comments to complete the analysis, I am glad you understood

"But if one accepts this, then it means that in-principle one could make as precise measurements as one wishes." - no, it doesn't mean that, and I don't know why you think it would. Saying "it has nothing to do with measurement limitations" means that even a perfect experiment free of all real-world imprecisions has these uncertainties, not that there exist experiments which bypass it. — ACuriousMind 20 hours ago

DanielSank

@Secret You don't have to post it.

I can read it ;)

The question is complex.

I'd like to complete our logical diagram of the question.

(I still didn't completely get it)

Secret

8:22 AM

The take home message is in order to kill this question, one need to kill D

and NO ONE has addressed D in the comments as far I have seen

DanielSank

@Secret I'm still working on understanding what is $D$.

...computing...

Secret

Thanksfully OP have reposted D

@ACuriousMind "...even a perfect experiment free of all real-world imprecisions has these uncertainties...". That is exactly my point when I say you can make either $\Delta x$ or $\Delta p$ arbitrarily small until uncertainty principle becomes manifest in the macroscopic world. — Zero 3 hours ago

user116211

@DanielSank: Phew!.... Done!!

user116211

0

Q: Why does the law of conservation of energy doesn't hold true when the work-function $U$ depends explicitly on $t\,?$

[...] the infinitesimal work $\overline{\mathrm dw}$ comes out as a linear differential form of the variables $q_i:$ $$\overline{\mathrm dw}= F_1~\mathrm dq_1 +F_2~\mathrm dq_2+ \ldots + F_n~\mathrm dq_n\,.\tag{17.3}$$ This differentual form is of prime-importance for the analytical treatment ...

classical-mechanics energy-conservation

Secret

(I will let you guys finish before I comment about the typical fate of questions like this. (It is a very common thing for any questions asked on the internet in general))

user116211

8:24 AM

Now, check @DanielSank, if it is clear or is still ambiguous; I'm really tired typing though....

DanielSank

@Secret First of all, bravo and my admiration for noticing that this post is interesting.

@MAFIA36790 Well, you definitely didn't need to include the entire excerpt XD

I think the logic is simple:

$$X: A \rightarrow B$$

$$C: \text{not }X$$

$$D: C \rightarrow E$$

user116211

@DanielSank hmm; I included what I though relevant so that no question arises on terminologies and terms again.

DanielSank

Note that $E$ is "we should observe large fluctuations in $\Delta x$ or $\Delta p$.

$$\text{By observation, }E\text{ is false}$$

$$\text{Therefore, by using contrapositive, }X\text{ is true}$$

@Secret I believe that's the idea, yes?

And yes, I completely agree that the interesting part of the question, which none of the comments or so-called duplicates address, is $D$.

Paging @JohnRennie and @ACuriousMind.

To summarize all at once:

Secret

Yes that's one way to kill the $D$ (which you rephrased it as $C \rightarrow E$). And now the interesting this is: why E is false

DanielSank

$A: \text{The Heisenberg uncertainty relation}$

$B: \text{There's a limit to the accuracy of physical measurements}$

$X: A \rightarrow B$

$C: \text{not }X$

$E: \text{We should be able to observe large fluctuations by making precise measurements}$

$D: C \rightarrow E$

We don't observe $E$, so by contrapositive, $X$ is true, and so $B$ is true.

@Secret is that summary correct?

Secret

8:34 AM

yes

and that's OP's question wrapped up in logic statements

DanielSank

We must address $D$ to kill the question.

But you were going to make a point about this being common on the internet.

I think I already see your point.

I agree!

Secret

Typical fate of these questions are: D was overlooked, OP want to clarified it is D, people lost patience for follow up questions and thus no extra response followed, question effectively abandoned, disatisfied OP

DanielSank

The author of the answers and comments must take time to understand why OP is confused. It's not enough to identify one particular proposition in the chain of logic, say that this proposition is false (and maybe cite stuff) and claim victory.

@Secret, I am very happy you brought this up. Often when I see these questions I just ignore them because I don't want to deal with explaining to OP that $D$ is the problem.

It's much, much worse when there are already statements by other users saying "NO YOU'RE WRONG BECAUSE B IS FALSE AND EVERYONE KNOWS THAT"

In such cases, I just move on, feeling dissatisfied.

Secret

For me I don't (because of my extreme hate of unanswered questions). This is why sometimes to professors and others (and even the chat) they thought I seemed to be interrogating them when I ask them questions, because I am guiding them to kill D

DanielSank

Note that ACM's comment addresses something that's not even in my summary.

Right?

There's actually another line:

$Y: C \rightarrow \text{We can make precise measurements}$

ACM basically said "$Y$ doesn't make sense".

Secret

8:42 AM

Yes and he also have not addressed D. So we can only say he only addressed X indirectly when using Y

DanielSank

I don't think ACM's comment address $X$ at all.

@Secret I strongly encourage you to make a meta post about this.

it is fascinating.

If you do so, please try to make the logical structure/notation very clear.

Secret

I am writing it now, but I am bad at titles, any suggestions?

DanielSank

@Secret "Killing the wrong node in a question's logical chain"

Secret

NICE!

2physics

Hi wrong node killers

:D

what's up

DanielSank

8:50 AM

@Secret Well, I did write the FAQ on titles :)

Secret

@2physics Dramatically speaking: We have identified the source of a very common phenomenon about questions that plagues the internet

It all thanks to my biology teacher of 10 years ago teaching me to think in terms of chains of logic

DanielSank

@MAFIA36790 I think your post could be improved.

user116211

@DanielSank sure tell me the place(s) of improvement.

DanielSank

@Secret I am very satisfied by this discussion. I'm glad I stayed up late this evening.

@MAFIA36790 I left a comment on the post.

@MAFIA36790 Show some effort etc. etc. The usual things with "homework" questions.

2physics

@Secret I read some of your chats but I didn't realize what this phenomenon about questions is, can you explain it?

user116211

8:54 AM

@DanielSank I think $F_i \ne \dfrac{\partial U}{\partial q_i} $ when $U$ is time-dependent.

Secret

@2physics Don't worry I am writing a meta post on it, because it is a very common issue in all questions asked in non face to face media

DanielSank

Hey @Secret in the meta post... it's good to use a real life example.

Note, however, that the real life example is a bit complex. It might be possible to come up with a simpler example. Unfortunately, that simple example wouldn't be from a real question.

2physics

@Secret ok thanks

user116211

My second query was that whether $V= -~U$ still holds when $U$ is time-dependent. i hardly doubt that, though @DanielSank

DanielSank

Your choice, of course. I think in the end, go with the real life example.

Secret

8:56 AM

I planning to use that question to illustrate the concept, we can add real life examples after that paragraph to flesh it out

DanielSank

@MAFIA36790 perhaps yes, just ask that.

It's much more focused.

@Secret Wait, what?

The post is a real life example.

I'm asking if it would help to make up a fake, simpler example.

user116211

@DanielSank oh; the author writes it is still true.

Secret

@DanielSank wait do you mean I should use a simplified example in the meta post, instead of using that question as an example? (As currently I am writing in the PSE meta)?

DanielSank

@Secret I'm not saying you should. I'm raising it as an option.

In the end, I think it's best to use the real question, as you are doing, even if it's complex, instead of a fake simplified example.

Secret

I always use real life examples to mount my point, thus don't worry

Because the truth is "It is that complex"

In fact, I am suspecting why answering questions are hard might be because asking question make use of second order logic

DanielSank

9:02 AM

I'm far too tired to read that.

:P

Secret

Do meta have mathjax?

cause I see only dollar signs

DanielSank

@Secret Nope.

Just do this:

X: A --> B

Secret

ok

2physics

sorry for interrupting, Do you have any suggestions for the ones like me who want to improve their english?

user116211

@Secret I've no idea of higher order logics :(

DanielSank

9:04 AM

@2physics That's a pretty general request.

Secret

@MAFIA36790 Me neither, I just did a brief skim thus I may be wrong (good thing I read fast)

DanielSank

In my experience, those who learn English well do so through movies, television, and speaking with friends.

Secret

but basically second order logic can have relations as propositions

2physics

I mean spoken English

DanielSank

@2physics What is your native language?

2physics

9:05 AM

persian

DanielSank

The only way to improve spoken English is to speak English :)

Hmmm... I was going to suggest Duolingo but I don't think it has English for Persian speakers.

You could check.

duolingo.com

2physics

yea, with english speakers, not with sb who try to learn it and make many mistakes which you may think they are true and may use those mistakes in your speech later

(I'm talking about people around me who are trying to learn it)

DanielSank

@2physics Yes, the only way is to practice with other native English speakers, and listen to English music, movies, etc.

:32502409 Hello

user228700

@DanielSank Hello :-)

2physics

you know my English is not that bad, but it really makes you feel bad when you are trying to explain sth in for example english and you feel you cant convey the meaning as same as your first language.

DanielSank

9:10 AM

@2physics Of course.

user228700

I've got a bit of a homework-tsy question. I hope u(or someone else) will feel inclined to help me out (:P) It's a very simple question and I want to know what's wrong in my line of reasoning, kind of.

user116211

Well @DanielSank, I've become mad with all these..... total unrest, hmm. Yesterday discussed things with ACM till 3.30 am; no sleep; I need to eat that book, but at every step, I'm getting hindrances T__T

DanielSank

@KaumudiHarikumar go on...

user228700

The question is this: "An ideal spring with spring constant k is hung from the ceiling and a block of mass M is attached to its lower end. The mass is released with the spring initially unstretched. Then what is the max. extension in the spring?" What I did, was use the fact that the block is in equilibrium and equated all the forces acting on it-the tension exerted by the spring and the weight of the block.

user228700

So I got Mg/k but the textbook has used the conservation of mechanical energy and come up with 2Mg/k.

2physics

9:15 AM

@DanielSank and sometime I feel I don't understand some english statements completely; for example, last night I was watching a video course , the teacher said "I read off from here" .. I wondered why doesn't he say "I read it from here"?? what does "off" mean here?!

John Rennie

@KaumudiHarikumar At the lowest point the mass/spring aren't in equilibrium because the mass bounces back up from the lowest point.

What you've worked out is the average position i.e. the midpoint of the oscillation.

DanielSank

@2physics It's an idiom.

user228700

@JohnRennie It bounces up..?

John Rennie

Yes, you let go of the mass and it starts to fall down. It falls down some distance then bounces back up to meet your hand again.

DanielSank

@KaumudiHarikumar At the greatest extension of the spring, the block is not in equilibrium.

When you release the block, it oscillates.

user228700

9:17 AM

@DanielSank Oh CRAP!

user228700

@JohnRennie Didn't use my brain effectively enough. Sorry :/

DanielSank

When you release the block, it oscillates.

user228700

Wait, it stops oscillating and settles at the equilibrium position at some point, right..? (This doesn't correspond to max. extension, I know. I just wanna understand what happens next)

John Rennie

@KaumudiHarikumar only if there is some damping. An ideal mass/spring would oscillate forever.

user228700

@JohnRennie OK. Understood. Thanks! :-)

Secret

9:21 AM

::Is going to use his wavefunction superpowers in the meta post::

John Rennie

A real mass/spring would be damped (by a non-conservative force!) and it would eventually come to a halt at the length you have calculated.

2physics

@DanielSank ok thanks.. you know they have translated everything here and they encourage you to use the persian words in math, physics and everywhere through high school and undergrad educations. and then when you start to study the papers which are written in english, or try to write prepare a paper in english, it's kinda hard to find out for example the word for various technical terms.

and you have to go and start to "read off from" elementary english math/geometry/physics books to learn the terms and statements you need! it makes you slow both in learning new stuff through the papers and books and asking questions also in publishing your work.

DanielSank

9:36 AM

@2physics That sounds frustrating.

2physics

yup :)

and when it comes to spoken english , it's way harder..

DanielSank

@2physics "Way harder", not "way more harder".

:)

user116211

Well, @DanielSank, can we define potential energy $V$ for a time-dependent work function?

DanielSank

@MAFIA36790 I'm way, way too tired to answer that right now.

2physics

@DanielSank yes, thanks

user116211

9:39 AM

@DanielSank sleep; sleep; go to bed :)

2physics

@DanielSank I'm confused; google "way more harder" .. many people use it.. how do I have to know which one is right .. this is the problem, to be or not to be .. lol

user228700

@DanielSank: Yeah, how come u're up SO LATE?! :O

user228700

Isn't it like 3AM over there?

Secret

@DanielSank meta post doen. I am currently looking for cross SE examples to enrich it, but check if this version is ok and make necessary edits

0

Q: Major issue in answering and judging questions: Killing the wrong node in a question's logical chain

This is a common phenomenon that plagues not just questions asked on PSE, but actually all of SE and any non face-to-face communication media: To begin, a question is actually built by a chain of reasoning and has a structure. Only by addressing an important node in the chain can a questiono be ...

discussion questions unanswered-questions

Physics Meta

0

Q: Major issue in answering and judging questions: Killing the wrong node in a question's logical chain

This is a common phenomenon that plagues not just questions asked on PSE, but actually all of SE and any non face-to-face communication media: To begin, a question is actually built by a chain of reasoning and has a structure. Only by addressing an important node in the chain can a question be a...

discussion questions unanswered-questions

Secret

9:57 AM

you are right, meta ,this stuff is so common to the point of eyebleed. Here's a cross SE example

3

Q: Why is : $ [ \mathbb{R} [x_1 , \dots , x_n ]^{ A_n } : \mathbb{R} [x_1 , \dots , x_n ]^{ S_n } ] = [ \mathfrak{S}_n : \mathfrak{A}_n ] $?

How to show that : $$ [ \mathbb{R} [x_1 , \dots , x_n ]^{ \mathfrak{A}_n } : \mathbb{R} [x_1 , \dots , x_n ]^{ \mathfrak{S}_n } ]= [ \mathfrak{S}_n : \mathfrak{A}_n ] $$ such that : $ \mathfrak{S}_n $ : the symmetric group $ \mathfrak{A}_n $ : the alternating subgroup of $ \mathfrak{S}_n $. ...

polynomials finite-groups field-theory galois-theory

user116211

10:37 AM

@KaumudiHarikumar: Please don't take offence for my editing- don't write such things; no one is getting offended here. This is silly. If your edit is just, yours will be accepted ;)

user116211

@yuggib o/

ACuriousMind

@DanielSank Well, I didn't close it as a duplicate (otherwise my gold badge would've closed it with the first vote directly), I voted unclear what you're asking.

user228700

@MAFIA36790 I figured that message would be received by only you. Damn. Sorry about that. Well, some people tend to get offended at such things so that's why the disclaimer.

Secret

Fun fact: It seems Chem SE is relatively free of the aforementioned phenomenon. Unlike other SEs, I have search through more than 30 pages and even their meta and found most questions are quite well answered

user116211

@KaumudiHarikumar As I siad, no one gets offended unless some offended words are used or something not just. If your suggested edit is legit, yours would be accepted. The box is meant for showing the crux of the proposed edit, btw.

user228700

10:49 AM

@MAFIA36790 OK, sorry. I'll keep this in mind.

user116211

@DanielSank: You didn't go to sleep?

user116211

weird.

ACuriousMind

After reading it again I see that I, well, really didn't understand the question. I've edited it heavily to remove all the superfluous pseudo-history and reopened it.

Secret

chat.stackexchange.com/rooms/44190/…

BioSE used to have a chat and is now gone, lol

Result from BioSE: Not as eyebleedingly common as in MSE and PSE, but still exists

Instead for the non-examples, an opposite phenomenon is observed: The OP is the one not very responsive to the comments

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