The h Bar - 2016-09-15 (page 4 of 4)

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10:03 PM

@0celo7 So I'll guess. (A) "Initial" means right after the fission and before they have had time to slow. (B) "Total" means either summing over the two heavy fragments or summing over all fragments including the neutrons. I'm inclined to guess the former because the latter is a considerably harder problem.

cool.. I agree but actually I've always used word and never had a problem. also there are many software packages that you can install on word to type any kind of equations and formula easily , maybe that's why many people like me don't try to change their usual methods and don't spend time on learning new tools

@Sanya My Father used word to do his thesis about 10 years ago. He didn't know LaTeX and it was what his advisor used. He backed it up several times a day at the advice of some fellow students and recent ex-students, and just as well: word ate his live copy several times.

@dmckee happened to me 2h before printing

thought I would go nuts

@Sanya I'll bet. Gives me the chills.

word ate his live copy several times. what does it mean sorry?

10:08 PM

@2physics That means the version he was typing on simply stopped opening. Totally corrupt. Restore from backup and throw away a couple hours of work.

I've heard a rumor that it does that less now, but I don't use it enough to know.

haven't happened to me yet.. but it has an option to save your work automatically for example every 30 secs.. I don't like MS products actually obviously their main purpose is to make money .. but it's not that bad using word. Although I agree what @DanielSank says and surely I'll start to learn and use Tex soon.

@Sanya how much did you pay for your MS word package?

@dmckee But how do you do d)?

I don't even know how to start c)

10:23 PM

@0celo7 Conservation of energy for D. Including the mass.

@dmckee conservation of what energy?

I don't know the initial energy of the uranium or the slow neutron

And treat the two heavy fragments as a two-body breakup for C. It's won't be much better than a 1% estimate, but so be it.

@0celo7 The initial nucleus can be taken as at rest, and they problem tells you the kinetic energy of the heavy fragments (part D actually nails down the intended interpretation of part C).

@dmckee So...I take the initial KE = 0?

Ignore the slow neutron?

@2physics I've had the autosave be corrupted :P

@dmckee So I get $BE=\frac{1}{2}m_{Ag}v_{Ag}^2+\frac{1}{2}m_{Rh}v_{Rh}^2$ and $m_{Ag}v_{Ag}=m_{Rh}v_{Rh}$?

where $BE$ is the energy from part b)?

No...

$160=\frac{1}{2}m_{Ag}v_{Ag}^2+\frac{1}{2}m_{Rh}v_{Rh}^2$

user218912

@0celo7 finally doing engineering?

yes, it's also harder than everything else

no clue what I'm doing

user218912

10:35 PM

xD

@IceLord so when am I getting my copy of Lee

user218912

for your birthday?

no

for being right about Shankar

user218912

I didn't bet.

user218912

I'm just blind or I don't know how to read.

user218912

10:38 PM

@0celo7 I have a question about lorentz transformations

user218912

$x^T \eta x$

user218912

what does the transpose do?

user218912

am I being retarded?

what is $x$

if it is what I think it is...yes, you are.

user218912

how come when you drop the indices and work in matrix form the transpose appears when proving that $\eta$ is invariant under lorentz transformations.

user218912

10:40 PM

$x$ is just a coordinate

user218912

it could be $\Delta x^T$

user218912

???

user218912

ignore that.

@0celo7 really?! sorry to hear that. dosn't it happen to Tex docs never?

10:55 PM

@2physics not that I know of

user218912

I figured it out @0celo7

@IceLord good.

user218912

it's basically just the definition of the dot product.

user218912

i'm retarded

correct

on both counts

user218912

10:56 PM

:)

user218912

@0celo7 wow :(

user218912

@0celo7 from now on on my retarded questions are you just gonna not answer and let me figure it out in the time?

user218912

because it works.

ok

ok?

@dmckee halp

for part d), do I set the KE of the 4 neutrons + KE daughters = binding energy?

so the energy from b) - energy from c) then divide by 4?

user218912

11:03 PM

@0celo7 how come you're doing graduate level math but struggling with first year physics when you once were doing graduate level physics?

@IceLord You would struggle with this too

user218912

nah

user218912

and that's dodging the question by attacking me.

Basic physics is extremely difficult

I don't know what's going on at all

user218912

perhaps...

11:05 PM

there's no way to know if what you're doing is correct

a mathematical proof is correct or it's not

a mathematical physics argument is correct or it's not

a basic physics argument can be bullshit through and through and still be "correct"

user218912

is that why you like math now?

yes

user218912

idk I find proofs boring

user218912

in linear algebra we were like spending an hour proving things about $\mathbb{Z}_p$

The only thing you know is 100% correct in life is a good proof

11:16 PM

@0celo7 what is a a good proof

@2physics glad you asked

user image

two very good proofs

user image

what

did you click on it?

yup it works

weird

well that's a good proof

what is a Watt, anyway

@2physics I have some favorite proofs

@SirCumference have you figured out the error of your ways

11:24 PM

@0celo7 No! You haven't showed me a darn source

for what holy crap

How on Earth am I going to find any error?

@0celo7 To this

Implying it changes more than a few microseconds

Day length fluctuations

The length of the day, which has increased over the long term of Earth's history due to tidal effects, is also subject to change on a shorter scale of time. Exact measurements of time by atomic clocks and satellite laser ranging have revealed that the length of day (LOD) is subject to a number of different fluctuations. These tiny fluctuations have periods which range from a few weeks to a few years. They are attributed to interactions between the dynamic atmosphere and Earth itself. The International Earth Rotation and Reference Systems Service monitors the changes. == Introduction == In...

idiot

I'm going to transfer laundry to the drier

I expect you to understand this when I come back

drier?

dryer?

the thing that makes clothes not wet

Dammit

Since when were you good with geology?

I thought you were a subatomic particle or GR person

I am a geometer

Geometry started off as the study of the Earth

11:27 PM

@0celo7 yea it looks beautiful. and this is also one of my favorites:

So you happen to know about geodesy?

user image

@0celo7 Wait, hold on a sec

user image

Isn't it just deviating by milliseconds?

it can help calculating $\pi$ digits

@2physics Can it? I mean, it can, but it's an alternating series with the denominator growing linearly so would probably take forever to approximate $\pi$ efficiently to say some $10$ digits.

Not very efficient.

11:38 PM

@SirCumference Yes.

@0celo7 Go back to not caring about planetary sciences

That's part of astronomy

@BalarkaSen Yes, it's horribly inefficient.

@BalarkaSen I think Newton used it to compute 43 digits by hand.

Pulling that number out of my ass, but it was something crazy.

the Leibniz formula can be used to calculate π to high precision (hundreds of digits or more)

poor Newton

Leibniz formula for π

See List of things named after Gottfried Leibniz for other formulas known under the same name. In mathematics, the Leibniz formula for π, named after Gottfried Leibniz, states that 1 − 1 3 + 1 5 − 1 7 + 1 9 ...

11:41 PM

@SirCumference Sigh.

Stop trolling.

Oh goddammit

@2physics Eh? No. Look in the section on "Convergence"

The speed of convergence is very, very slow.

Like I said: "Calculating π to 10 correct decimal places using direct summation of the series requires about five billion terms"

Say, probably a stupid question, but did Newton ever say $F = \frac{dp}{dt}$? It seems more likely he'd say something like $F = p'(t)$

My teacher always said he said the former

I see you're quoting from below "high precision etc" but accelerating that series would not give you the same formula.

He would probably write $F=\dot p$ because that's his notation.

11:43 PM

@0celo7 I thought Newton's notation for derivatives used $f'(x)$?

Certainly not for time derivatives

@0celo7 Oh really? My teachers never mentioned that

@0celo7 You don't care for astronomy?

@BalarkaSen Nah

@BalarkaSen He lives a poor life

11:44 PM

Why not, @0elo7?

@BalarkaSen Don't see the point

Well he seemed kind of interested when he asked that question about charge coupled devices

the point is to go through a wormhole and time-travelling of course

@SirCumference don't remember that

@BalarkaSen You mean time dilation? That's the only way I see time-traveling happening

@0celo7 Here, 0celo

11:46 PM

I mean time travelling.

scifi 101

@BalarkaSen What do you mean, time traveling?

@SirCumference That was for a class I am not willingly taking.

@BalarkaSen don't see the point

@0celo7 Oh. So did I help you out then?

no

...I'm trying man

11:47 PM

@BalarkaSen I did. it still "can help calculating $\pi$ digits" and also one of my favorites :D

You crush me...

sure, it's a nice formula, @2physics

@BalarkaSen The closest thing I can think of is time dilation

Which theoretically could work

uhhh

dude. i am speaking scifi, not special relativity

don't be tedious like 0celo

11:48 PM

8.1E6 kg coal in a day seems like a lot

:P

@BalarkaSen I thought you were talking about astronomy?

nah

D:

I don't know crap about astronomy.

11:49 PM

See, this is why I've never watched star wars

or star trek

heh

me neither

They seem too fake and outlandish

weirdos

@0celo7 Welcome to Physics SE chat!

In seriousness, the amount of astronomical innacuracies in space movies is, well, astronomical.

I don't think writing a textbook on general relativity is the point of space movies.

11:51 PM

weird you would say that

@BalarkaSen Nah; real space movies would involve incredibly dangerous, sickening and boring trips

currently holding a GR textbook

...are you watching me @BalarkaSen

Being trapped in a cramped space ship, your body falling apart with no gravity...

But yeah, when people say they know everything there is to know about general and special relativity from watching "Interstellar", that's something

@BalarkaSen Tell me about it

11:52 PM

*Interstellar

(I think)

I've seen so many questions on Astronomy SE about things people have seen in Interstellar

@0celo7 Nope, you're right

@BalarkaSen are you doing dimensional analysis in school

kinda sorta

Then there are questions like this

user image

worldbuilding.SE

11:54 PM

@BalarkaSen I need to convert 3000MW to kg coal/day.

All three parts of that question are cringeworthy...

I got 8.1E6

seems like a LOT

but maybe 3000MW is a lot

then again 3000MW is 4kg Uranium

But seriously @0celo7, I never understood how you could be apathetic towards astronomy

so that is a lot

I mean, it's got loads of GR and QM

11:55 PM

@SirCumference Does absolutely nothing for me

@0celo7 So?

@0celo7 yikes lol. you mean you want to find out how much coal you need to burn a day to get 3000MW power?

Isn't it cool at least?

I don't see the purpose.

@BalarkaSen it's interesting that more than 2 hundred years before this formula being proposed for pi with 10 correct decimals. sb has calculated it to 16 decimal places of accuracy and hardly anybody knows about him.

11:55 PM

@BalarkaSen Yeah.

@0celo7 Okay, so what's the purpose of nuclear physics?

coal burns at 32 kJ/g

Or QM?

@SirCumference Bombs

Or GR?

11:56 PM

I'm just checking to make sure I didn't make a stupid mistake

In his numerical approximation, he correctly computed 2π to 9 sexagesimal digits[11] in 1424,[3] and he converted this estimate of 2π to 16 decimal places of accuracy

@BalarkaSen Perhaps...though I'd hope you guys aren't planning to make bombs

lemme write out the calc

I am not, for sure

I do humble math

$$3000MW=3\times 10^6 kW=3\times 10^6\frac{kJ}{s}\times\frac{24\cdot 60^2s}{1d}\times\frac{1g}{32kJ}\times\frac{1kg}{1000g}$$

11:57 PM

@BalarkaSen You an astronerd? Physics nerd? Or just interested in pure math?

@SirCumference Bombs, yeah.

@0celo7 ._.

No, but besides destructive capabilities?

There's not much "useful" in theoretical physics. It's just an amazing subject.

Peace keeping, not destructive.

@0celo7 Okay, try and add nobility to weapons of mass destruction

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