The h Bar

1:24 AM

@Real I agree. If we would be around 10 times more, it had probably a significant chance

@Real The main problem with the current system, that it creates continous conflicts and sick directives (f.e. closing and later deleting interesting exercises), while it is not really attractive for research level members.

David Z

@Real We've tried that before. It was a rather spectacular failure.

@Ulthran What @DanielSank said, and also, learn math. Being very comfortable with calculus is a huge advantage. If you do go into physics as a career, then later on you will have the chance to specialize somewhere on the spectrum between theoretical and experimental physics. For theory, you need to know math very well, and for experiment, you need to be good with tinkering.

2physics

1:40 AM

I have a question about the papers on arxive.org website, I wanna now if they publish any paper? Are their published papers peer reviewed? and if people can refer to its papers?

anybody can help?

0celo7

@2physics are you the guy with the grandpa

2physics

@0celo7 what do you mean?

@0celo7 I don't know.. maybe I'm the grandpa :D does it make difference?

0celo7

perhaps.

did you make a post about your grandpa

2physics

no

why did you ask?

0celo7

1:58 AM

clearly someone was asking about their grandfather

2physics

@0celo7 okay, it was not me.

@0celo7 both of my grandpas have passed away.

@0celo7 can I ask a question related to the nuclear physics here?

0celo7

yes

We do not guarantee you will get an answer

or that if you do, it is correct

2physics

alright, I haven't searched it yet btw.

when the electron is in its wave form, what makes it bounded(didn't find a better word! lol) to the nucleus?

if you want to explain it to a high school guy, how'd you do that?

0celo7

2:19 AM

Dunno, I'm not a physicist

2physics

@0celo7 thanks.

DanielSank

2:33 AM

@DavidZ FWIW being good at math makes experiment a lot easier too.

0celo7

@2physics np

@ACuriousMind I took a 3x3 determinant correctly oh I'm so happy

Ulthran

@Ocelo7 Now try a 5x5

0celo7

@Ulthran I'm not in high school, so no.

Ulthran

@Ocelo7 :P Is that so useless it can only be done in high school?

0celo7

yes

currently doing quantum mechanics homework

Ulthran

2:44 AM

Currently on my 15th hour of stoichiometry... So... Much... Fun...

0celo7

to be fair I use stoichiometry a lot at work

What do you do?

undergrad research

Chemistry?

solid state physics

2:46 AM

Ah

I would imagine it's a bit more fun when you're doing it as a means to an end rather than just doing questions 1-99a-z though

0celo7

it's not fun

and it's one calculation

then you make the thing

Secret

I just figure out possibly the simplest proof that division by zero will collapse any algebraic structure it is present in:

Suppose we have a set with elements a,e and closed under @. Given two axioms 1) a finite sequence of e@e@e=a and 2) e is an identity under @. Then by closure a@a=e or a@a=a

However note that by axiom 1, a@a=e@...@e@a. Then by repeatly using axiom 2 we get a@a=a. Thus if a is not at least a neutral element of a we have a contradiction. Moreover by using axiom 1 twice a@a=e@...@e@...@e. Using axiom 2, we get a@a=e

Therefore a@a=e=a. Thus the set has only one element e QED

Shing

3:09 AM

I am almost driven crazy, it took me so long, but I still can't figure it out how to install numpy into my python

Secret

What is numpy?

0celo7

something that rhymes with lumpy

Shing

3:49 AM

@Secret a package in Python to do linear algebra/scientific computation

Noah P

6:45 AM

chat.stackexchange.com/transcript/message/31873112#31873112 Aww @JohnRennie

alarge

7:16 AM

@2physics arXiv is a preprint website, so most things there have either been submitted or already published in a peer reviewed journal. You can cite papers off of arXiv, but typically you'd cite the version that got published (but in some fields the review process may take too long).

@Shing If you're on Windows, the easiest way forward is to probably use Anaconda or some other Python distribution. On other platforms the problem doesn't really exist.

@BernardMeurer How about checking out the courses on Coursera, edX or Khan Academy, and if you're not into watching videos, see what books they recommend.

John Rennie

@NoahP :-)

@SirCumference: you don't need calculus to analyse linear motion in special relativity. However you do need calculus to understand accelerated motion. Even if you are only interested in linear motion, understanding the (very simple) differential geometry that describes SR will make a huge difference to your understanding of SR.

But unless you're 0celo7 and doing screwy calculations for fun, only a basic understanding of calculus is needed to understand SR well.

John Rennie

8:02 AM

@NoahP BTW I passed the info about Crest on to my brother, and it's something the school already does. He mentioned there's a similar scheme his school does called Headstart - I don't know if you've ever come across that one.

Noah P

8:21 AM

@JohnRennie I've heard of them, but I don't think our school offers them

@JohnRennie @DavidZ Do we call this homework?

0

Q: How to prove my mathematical induction that a pendulum follows SHM?

Could someone please tell me how I can prove that a pendulum is following SHM. I know the differential equation and the angle I used is 20 degrees. It is also fine if the proof or conjecture is by lagrangian mechanics. Thanks.

mathematical-physics

John Rennie

I'd close as insufficient prior research, though I've given the OP a chance to respond.

Noah P

Okay

@JohnRennie When a magnet attracts a metallic ball, would I be correct in saying that the energy is drawn from the magnetic field and transferred to KE of the ball?

John Rennie

It's not as simple as that.

If you consider an isolated system there is an energy stored in the magnetic field. For example if the isolated magnet was an electromagnet you would need to put electrical power in to create the magnetic field.

However when you have two objects the total energy is a property of the system and can't easily be pinned down to any single object.

Noah P

But would the introduction of a steel ball then reduce the magnetic potential of the magnet and increase its own?

And then the MPE of the steel ball is transferred to KE as they are attracted?

John Rennie

8:36 AM

Not necessarily. I don't see any reason why the presence of the unmagnetised ball should have any large effect on the magnetic field.

Noah P

So when it is attracted to the magnet, where on earth is that energy coming from?

There must be some sort of negligible effect?

John Rennie

Potential energy doesn't have an absolute value. It looks as if we must be getting energy from nowhere as the ball falls in, but that's only because the absolute value of the potential energy isn't defined.

Noah P

Okay

John Rennie

The way to look at this is to consider a cycle involving letting the ball fall in, then taking it back out to it's original position.

Noah P

That makes alot more sense

0

Q: Does a magnet create energy?

I know what i am asking is not possible , but the scenario what i am pondering over I cannot explain. So let's assume their is a huge magnet subtending from the top of the burj khalifa (Tallest building, Dubai). The magnet is so powerful it can pull objects from the ground below. I keep a series ...

electromagnetism

See the first comment; completely non-sensical IMO

John Rennie

8:43 AM

If you find you can get a net amount of energy out there's obviously a problem because you'd have non-conservation of energy.

But as long as the net energy change balances out to zero there's nothing to worry about.

Noah P

@JohnRennie You call that a problem? I call it a miracle, and a solution

John Rennie

If it's any consolation I remember getting very puzzled about exactly this point as an undergraduate. It seemed to me that there must be negative energies involved, which i found most disturbing.

Noah P

::shudders::

Secret

0

Q: Prove, give counterexample or show trivial conclusion of the existence of mathematical objects with empty sentences?

Recall in classical logic a sentence $\phi$ is a boolean valued statement that may be true or false (To narrow down the scope, we restrict ourselves such that the empty string has its usual properties being an identity element wrt concatenation). Then $\phi(M)$ is a statement about some mathemati...

proof-writing formal-languages

My experience told me that I have to be careful not to let any of my questions closed. Because my questions are generally too weird that once closed the chance for them to reopen is close to zero no matter the edits

Put it in another way, once the question is closed, people will have an excuse to no bother about it anymore because there is too much weirdness to resolve in order to make the question meaningful

I am kinda glad this phenomenon is less common in my experience in PSE because physics have restrict the number of possibilities of me asking weird things

Another phenomenon is that generally, even if an edit is done to the question to clarify concerns raised in the comments, most people generally don't retract their close votes. Therefore, my philosophy is that you must get the question right before it attract the first close vote as once that happens, you are done and it will be closed

Noah P

9:03 AM

@Secret Completely agree with that

See the comments of this question:physics.stackexchange.com/questions/269040/…

Secret

To me, most of the time, if a quesion is closed it is the same as the community saying the following:

"This question is not interesting, and we don't fucking care whether you will elaborate that to us because we don't bother to understand"

Noah P

I think that's a little harsh @Secret

Secret

well, maybe that's only for a few cases where the comments are not being read by the users. I have seen couple of examples where there are no response when the OPs ask for clarification in the comments and try to fix their questions

for PSE, this phenomenon is more common in the homework like questions

The good news is that at least for PSE, based on the latest correlation data DavidZ collected, close votes are not strongly correlated to interest, thus when we finally fix that homework like closing reason, there is a way to improve the situation

David Z

9:58 AM

@NoahP eh, I wouldn't, but I would consider it unclear

@Secret I might have goofed up that analysis a bit - I fixed some issues with it and the interest correlation came back, though not as strong as before. Anyway, I'm currently working on a meta post with details.

Secret

ok

Emilio Pisanty

11:16 AM

@JohnRennie Can I ask what this was?

Emilio Pisanty

11:29 AM

It looks relatively close to the money to me, though there's still some way to go in firming it up.

John Rennie

11:46 AM

@EmilioPisanty We were having yet another ~~argument~~ constructive discussion about the homework policy and Daniel challenged me to provide a definitive description of the current policy. That was my attempt. I left it deleted so that only the high rep users would see it.

But Daniel doesn't agree with that policy, ACuriousMind seems ambivalent and DavidZ says it's pointless anyway as the idea is to eliminate the term homework from the policy.

As of right now I have absolutely no idea what any changes are intended to achieve. That answer is the way I think things should work, but I seem to be in a minority of one.

Emilio Pisanty

12:04 PM

@JohnRennie That's a grand state of affairs.

John Duffield

@NoahP : it isn't. You do work when you pull the magnet and the ball apart. In similar vein you do work when you lift the ball. It's all fairly straightforward stuff, see my answer. The books always balance.

2physics

@alarge thanks. so, since some of the submitted papers may be rejected by the referees of peer reviewed journals , therefore we can't cite the papers on arXive I mean we better not to use them as references. right?

Noah P

12:18 PM

@JohnDuffield Answer looks good, but what if I had two steel balls at a distance, and then I instantaneously magnetised one? Then theres no work done in moving them apart (I see they your answer addresses this, but the comment I replied to did not)

John Rennie

@EmilioPisanty Tell me about it :-(

alarge

12:41 PM

@2physics Sure you can use them as references. Peer review is no guarantee of correctness either. If the paper did get rejected, it'll probably be resubmitted to some other journals until it goes through.

2physics

@alarge yeah, you're right.. thank you for your answer & help.

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