12:01 AM
Ah, haha, nice!
(Y)

12:41 AM
@dmckee Assembled with a couple other grad students (that are vastly more experienced than me) a "1%" prototype of the "millicharge" particle detector. I didn't realize gain variances between PMTs were so high.

OK, a silly question had me envisioning what has to be the silliest piece of NIM plug-boarding done in quite some time:
Now, you could DAC the data, smooth the output with an appropriately chosen analog filter, split the line, differentiate one half with an op-amp then perform an analog zero-crossing detection and use the output to latch the other signal (which has gone into an appropriate delay line) and finally ADC that to get your answer. I could even wire the analog part in NIM if I had a big enough cache of modules and couple of crates, but ... it would be silly. Really, quite silly. — dmckee ♦ 13 mins ago
@GPhys Yes, the gain matching step of any compound PMT-based detector is time consuming, picky, and very important.

@JohnRennie need physics assistance

our signal looks like single photoelectrons - test setup is going to be shipped to CERN with 12 cooled PMTs to be installed at an unused drainage tunnel near the CMS interaction point
I guess the idea is that after the setup is demonstrated working, then everybody involved can apply to fund the full experiment

@GPhys Prototypes are great fun because they are small enough to understand in toto, quick enough to follow through all stages of the project, but real enough to be relevant.
You'll learn all kinds of stuff on that kind of project.

1:34 AM
space-waves! theyre called LIGHT! o_O

@Secret that is an awful way to think about things

2:22 AM
@rob I need someone worldly
@dmckee an experimental physicist could work

@0celóñe7 I wasn't paying attention. Am I worldly?

@rob paying attention to what?
you sound worldly

@0celóñe7 What do you need?

@rob I need to raise a monitor ~4"
what common items can I use to put it on
not books

@0celóñe7 Bricks. They're cheap at hardware stores if you don't like the ones you find lying around outdoors.

2:26 AM
@rob is there a brick getting place in Knoxville
near Vol Hall preferably

@0celóñe7 Lowes/Home Depot

@rob I can't see myself going there at 2230

@0celóñe7 This has to be done now?

@rob ideally, yes
I used books for the same purpose at home

@0celóñe7 Use books that you're not planning to read before you go to the hardware store tomorrow.

2:29 AM
but here I don't have books I want to prop up a monitor with

Were you planning to read every book you own tonight?

@rob no

@0celóñe7 Problem temporarily solved

@Slereah up early?

Yep

2:46 AM
@Slereah what are you up to

Working on my vidyah gehm
the boring parts
User interface

my books seem to have broken this shelf in my apartment
trying to avoid it completely collapsing
@Slereah do a better job than bethesda

Gonna be hard
I'm no UI expert and I work alone

3:08 AM
@Slereah Bethesda has no UI experts either

Bethesda does that lazy thing where they use the same UI for both consoles and PC
Even though the UI is completely different

@rob @BalarkaSen found a use for some topology books

-1

Many a times, there are questions which are absolutely vague and have no meaning in them, like: If I fall from a great height, will I overcome the speed of light? Now, these are off topic questions, but there are no proper flags for this. Generally I flag this as very low quality, but many times...

3:47 AM
@0celóñe7 angry reacts only

4:00 AM
@BalarkaSen name two books better suited to the task

4:26 AM
Hey, I want to know, the speed of a particle which is thrown with initial velocity u, when it's at half of it's maximum height
(it's thrown vertically upwards)

@RaviPrakash find the energy, get the velocity from the energy.

I got the answer as u.
'u'
Is it correct
@EmilioPisanty I have never tried finding that way
Are you showing? @EmilioPisanty
I did: v = √(2gh) , put h=(u^2)/2(2g) and got v as u/√2
(earlier I did a mistake, I putted h as u^2/2g) :P

looks ok to me

I also think :)
Can I ask one more thing @EmilioPisanty :)
Tell what is the acceleration of particle under projectile motion at the highest point of its trajectory

4:41 AM
gravity

Yes!
Me too..
If a ball thrown up is caught by the thrower after 4 seconds then the maximum height attained by the ball will be: what?
I think it's 20 m

Landau&Lifshitz takes up like a third of my book room and I don't even own the entire series

I did: got that h = u and so h = u^2 / 2g , which gives h = 20
Am I wrong?
since for upward journey, h = 2u - 1/2•g•t^2 and for downward it's h = 1/2•g•t ^2 solving these two gives h = u, is it possible
Okay, leave these..
How many of you have given International Physics Olympiad

5:00 AM
@RaviPrakash gravitational acceleration
0

Steady state with respect to the rod being heated from one end is the state when the temperature of each section of the rod becomes constant. Now, it's very similar to equilibrium but I wonder if it's possible to reach this state before equilibrium. If yes, how? Moreover, heat is always going t...

Good morning @JohnRennie

Morning :-)

2 hours later…
6:55 AM
Morning

7:06 AM
Mornin'

@JohnRennie If a ball thrown up is caught by the thrower after 4 seconds then the maximum height attained by the ball will be: what?
I think it's 20 m.... Am I correct

Hi Ravi

Hi John
I'm from India

Ignoring air resistance the trajectory is symmetric i.e. the ball spends the same time going up as it does coming down.

Okay
Then?
That means 2 sec

7:09 AM
So the ball starts with some velocity $u$ and takes 2 seconds to get the top of its trajectory at which point the velocity is zero.

Yes

Then it takes 2 seconds starting with zero velocity to fall back down to the ground

Using that idea, h = 2u - 1/2•g•t^2 and for downward it's h = 1/2•g•t ^2 solving these two gives h = u
(as for downward, u=0)
so h = u^2 / 2g , which gives h = 20m

Yes, the equation that relates distance to time is $$s = ut + \tfrac{1}{2} a t^2$$

Yes, it's second equation of motion

7:12 AM
If we just consider the downward part of the motion we know $u=0$ and $t=2$

:) yes

So we get $$s = \tfrac{1}{2}g ^2 = 2g$$

I too put the same logic as you
Then 2u = 2g
Cancelling 2 from both sides , u = g

The equation that relates velocity to time is $$v = u + at$$

Yes

7:14 AM
Again considering just the downward part of the trajectory we have $u=0$ and $t=2$ so $$v = 2g$$

Okay, then

It is 2g, not 20m.

Oops, ignore that!

Unless they have specifically asked you to take g=10.

Yes because I take g = 10m/s²

7:18 AM

Then, don't

What i take the value of 'g' does it affects the final answer?

@RaviPrakash: it's nice to leave things like $g$ as symbols unless a question specifically asks you for a numerical result.

Not by much. But, it is just "wrong" to take g=10.

7:21 AM
Yes
Then, if i leave it as 'g' then what to do next ?

Because g is never 10

It helps you see the importance of parameters like $g$ in your equations, and it means you could in principle use the equations on other planets where the gravity is different from Earth.

@JohnRennie Yes, i got it.... :)

What to do after i got v= 2g
In downward part of journey?

7:23 AM
Wasn't the question about max height?

Yes

Didn't you get the answer to be 2g?

Yes

Cool. Hope we have been helpful. :-)

Yes, and special thanks to @JohnRennie

7:28 AM
@RaviPrakash you're welcome :-)

Anyway, I need to rush off to college. Good day all.

Cya

From where all of you are?
US
Can white holes exist?

it is unlikely

I think its a situation when a black hole is too massive that it brusts releasing massive amounts of energy.... (I m not sure, fully ..)

7:41 AM
No, that is not how white holes work

@RaviPrakash I'm afraid the usual science fiction descriptions of white holes are wildly inaccurate. A white hole is a theoretical object that is effectively a black hole but with time running backwards.

I'm not 100% sure what scenario would be a white hole creation

However a white hole, at least the simplest type of white hole, requires the universe to have existed for an infinite time, which obviously isn't the case since the Big Bang was only 14 billion years ago.

I suppose it would be the black hole evaporation backward

So it seems very unlikely that white holes actually exist.

7:46 AM
Which would be... positive energy flowing inward, negative energy flowing outward
Which I don't think is a likely scenario

Not to mention, the possibility of all the various shades of grey holes in between :-)

8:19 AM
is black hole a non manifold point or just like a point of singularity of the metric
what even are these shitz

a black hole is the region inside the singularity
it's just a subset of the manifold
the singularity is part of the completion of the manifold

isee.winrar

@JohnRennie I too agree. Do you know what incident happend in 2006 like gamma ray brust

@RaviPrakash you mean GRB 060614? These guys suggested it might have been a white hole but I suspect most astrophysics think this is rather fanciful.

8:46 AM
We should have a "solar eclipse" event in here, no?

Black holes can be defines quite fancily

@JohnRennie yes, its fanciful..... If white holes were to exist, why do they disappear after short time..

A black hole is defined as $\mathcal{M} \setminus I^-(TIF)$
or something similar

why we don't have mathjax here in chat?

21

As a workaround while this request is pending, there exist several client-side workarounds that can be used to enable LaTeX rendering in chat, including: ChatJax, a set of bookmarklets by robjohn to enable dynamic MathJax support in chat. Commonly used in the Mathematics chat room. An altern...

8:51 AM
We do^ @RaviPrakash

How @skullpatrol

Click on the question.

I did but i didn't got how to.. Help me

instructions are given here: math.ucla.edu/~robjohn/math/mathjax.html

Those are the best instructions^ @RaviPrakash

8:56 AM
Okay

2 hours later…
10:49 AM
"everything was solved 100 years ago
todays physicists are theorists"
How did I miss this?
Also, someone please teach me how to quote a message.

> Quote
Ok, so that works
Do "> Quote". Make sure to put in the space.

> Balarka

> Rats I don't know your name

No but, how do you quote it in a way that the sender's username is also displayed?

Oh, huh good question
Why not just put in a -
> Also, someone please teach me how to quote a message - Avantgarde

10:55 AM
lol not very legit :P

#simplelifehacks

Don't believe everything you read on the internet - Newton

lol

It's everyday bro - Jake Paul

England is my city - Nick Crompton

11:10 AM
@Avantgarde When did Newton have internet?

@Avantgarde you mean like this?
16 mins ago, by Avantgarde
No but, how do you quote it in a way that the sender's username is also displayed?

in The Sphinx's Lair, 8 mins ago, by Wen1now
If you put 'of the day' in front of anything, it makes it sound really important. Also, sometimes people make the assumption that you'll give more things 'of the day'.

Of the day of the day: Of the day

I've just bought myself this:
i.e. a giant mouse mat. And it's great.

Mouse mats are pretty good. But isn't that too big?

11:18 AM
For years, decades even, it's been annoying me that mouse mats always slide around a bit when you move the mouse. But this mat is big and heavy and the weight of the keyboard holds it in place.
So, finally, I have a mouse mat that DOESN'T MOVE!

Can you move the mouse smoothly over that?

Yes, it's topped with fabric just like the usual small mouse mats.

How much did it cost? :^)

Euros or pounds?

11:25 AM
Pounds sterling my good man! Pounds sterling!
We Brits don't use Euros!
Though the way the exchange rate is falling any day now the pound will only be worth one Euro.

It is close to 1 Euro, no?

Anyone else from UK get A/AS grades today? :/

It was worth 1.4 Euros before Brexit!

That's a good deal with the 6 month warranty.

11:28 AM
The pound was strong during mid-2015. It has been falling freely since.

Whether a six month warranty on a mouse mat is worth anything is debatable. It's not as though it has any parts that could go wrong.
£5.75 is probably quite a lot by Indian standards, but I bet if you were buying it in India it would be a lot cheaper.

@JohnRennie never heard back from you...

@0celóñe7 what did I miss?

I have a shelf above my desk that might collapse
I need to know how to know

How to know whether it will collapse?

11:39 AM
Yes
It makes some creaking noises
I had it full of books
Then I removed half

I doubt it's possible to predict a collapse. You'd need to know the strengths of all the joints and the only way to measure those would be to stress it to the point where it fails, in which case the point is moot.
Work out the largest weight you're every likely to put on it, then load it to double that weight. If it survives you should be fine. If it fails you're down one bookcase but at least it didn't fail when you had something fragile and valuable on it.

If it breaks I will get charged for it
I'm not worried about what's on it, but my monitors are right below

@0celóñe7 I bet the amount you'd be charged for the books case would be a lot less than cost of replacing your broken monitors!
You could try moaning at the landlord to fix the shelf.

Anonymous
@CooperCape I don't think we've any A level guy here other than you. Have been seeing a lot of FB posts about this since yesterday.

Anonymous
@0celóñe7 Just empty the shelf (?)

Anonymous
11:50 AM
Why take risk...

Oh damn... I only had one AS anyway 'cause we've kind of given up on doing AS exams now...

@Blue cuz it looked nice with books up there
Ridiculous that it seemed to be unstable only half filled

Anonymous
@0celóñe7 lel.

Anonymous
:D

Anonymous
It will look worse if it breaks :P

Anonymous
11:52 AM
Now that I'm taking carpentry classes I think I can easily fix broken shelves. Hehe

This thing looks pretty stable though
I'm surprised the books were an issue
I guess I can put more on my actual bookshelf...

Anonymous
Just learnt the derivation of HUP. Feeling great! :D Oh my dear Cauchy Schwarz :)

I guess this works too
quick book access

Anonymous
I keep my books on a sofa beside me. Too lazy to walk up to the shelf

@JohnRennie does this count as cable gore?