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ACuriousMind
ACuriousMind
12:02 AM
@dmckee Emilio has posted it before, and I think you've also reacted to it before
 
DanielSank
DanielSank
@ACuriousMind ::Tosses potato::
 
ACuriousMind
ACuriousMind
I still can't tell whether Lego Grad Student is dark humor or just depressing.
@DanielSank ::activates automated anti-potato defense system::
(Yes, I have taken precautions for @BernardMeurer's eventual stab at world domination ;) )
 
Bernard Meurer
Bernard Meurer
If by stab you mean success I might just let you survive
 
vzn
vzn
 
Emilio Pisanty
Emilio Pisanty
12:18 AM
@dmckee no, it's a thing. It's pretty new but it's got a hell of a voice, you should check it out. Only problem is it's maybe the bleakest commentary on grad school ever.
I've posted some highlights here before, I'm sure search will bring them up easy
 
dmckee
dmckee
I read the more recent ten pages or so. I identified with bits of it, but didn't want to get into it in more depth.
 
Emilio Pisanty
Emilio Pisanty
Fair enough
There isn't all that much back material tbh
 
vzn
vzn
@EmilioPisanty nice work, reminds me of phd comic. saw the movie somewhat recently, not bad. that reminds me, a lego movie sequel is coming out soon (early) next yr, a lego fanatic salesman in the store just told me... did you see the 1st one?
 
Emilio Pisanty
Emilio Pisanty
@vzn yeah, much the same vein
Except Jorge Cham started head school well past a decade ago, and he pretty much ran out of steam, I think
 
vzn
vzn
@EmilioPisanty lol so did watterson :P ... theres a great documentary on him too... saw it, liked it... :)
 
Slereah
Slereah
12:24 AM
"Anderson and DeWitt were the first to consider the free scalar field in the trousers spacetime. They argued that the crotch singularity produces an infinitely bright flash, which was interpreted asevidence that the topology of space is dynamically preserved. "
Intensely bright flash at the crotch
I like Krasnikov
He is just so very determined to show that time travel is real
 
ACuriousMind
ACuriousMind
12:44 AM
@Slereah Was there really no better word for it than the "crotch singularity"?
 
Slereah
Slereah
@ACuriousMind Due to the topology of the spacetime, it is actually a naked crotch singularity
 
ACuriousMind
ACuriousMind
Wonderful
 
Slereah
Slereah
Do string theorists also like to have fun?
I know they do a lot of pants diagrams
Is there a crotch interaction
 
ACuriousMind
ACuriousMind
Well, you can build all of the 2D manifolds that are the "Feynman diagrams" for string perturbation by gluing pants together
But I don't think they have something that can rival the crotch singularity
 
Slereah
Slereah
that's a lot of pants
the trouser spacetime is pretty poorly known
I've seen like two papers talking about it
 
user228700
12:58 AM
I started a bounty on a Chemistry question and it's ending in 11 hours. Please, if anyone has any thoughts relevant to my question, think about posting them as an answer. I still haven't accepted the single answer that I've received so far:
 
user228700
 
ACuriousMind
ACuriousMind
@Kaumudi I have no idea what the "inductive effect" in chemistry is, but I don't see what is unsatisfactory about the given answer
I read the question and the answer and had a rather strong impression the given answer actually answered it.
 
user228700
No, not fully. The 2nd part of his answer is really confusing. We just had a small discussion at The Periodic Table and still didn't reach any sort of consensus.
 
ACuriousMind
ACuriousMind
@Kaumudi I'm afraid I don't see what's confusing about it, but then again I don't know much about this sort of chemistry
 
Slereah
Slereah
1:54 AM
Is there a smeared version of GR
Where quantities are measured over test functions
I think the Colombeau version of GR is
 
Sir Cumference
Sir Cumference
@ACuriousMind Want to see a magic trick?
 
ACuriousMind
ACuriousMind
Does it involve rabbits?
 
Sir Cumference
Sir Cumference
2:12 AM
@ACuriousMind No :/
 
Slereah
Slereah
2:45 AM
I am currently marathoning Enterprise
The worst of all Star Trek
 
ACuriousMind
ACuriousMind
Your masochistic trait is more pronounced than I ever imagined :P
Although I recently tried to rewatch DS9 and it didn't go too well, either. I didn't remember the acting being that wooden.
 
rob
rob
Heh, I just started re-watching DS9 and I had the same thought. But given the difference between TNG season 1 and the "good" TNG, I'm prepared to hold out for a while yet.
 
DanielSank
DanielSank
@rob DS9 is awesome.
 
rob
rob
I remember that discovering TNG on television as a kid changed my life for the better ... but if a rerun came on where Riker didn't have a beard, it was pretty safe to shut the thing off.
 
ACuriousMind
ACuriousMind
3:00 AM
Hm, I fear if I try to watch TNG again, my nostagia might take a critical hit :P
 
rob
rob
I was excited when DS9 started, but never really got into it ... I wonder whether I watched the first season and never went back.
 
ACuriousMind
ACuriousMind
In contrast to DS9, Babylon 5 was as good as I remembered it when I watched it again.
 
rob
rob
It's definitely more painful to watch Star Trek now that I know more about science than their writers did.
The thing that gets me most is the spurious precision.
"We've contacted these aliens for the first time, and their deflector shields have INCREASED BY TWO POINT FOUR PERCENT, OMG"
 
DanielSank
DanielSank
@ACuriousMind TNG doesn't stand up that well for me.
Some episodes are great, but the show as a whole is less so.
DS9 is a lot more watchable as a show for me.
 
Slereah
Slereah
3:21 AM
Well
I tried to watch Enterprise before
And I gave up
But I'd like to say
I watched ALL of Star Trek
And it's the only one left
 
rob
rob
Next you have to read all the paperback novels, though.
 
Slereah
Slereah
nah
I'm fine with it
I don't think it's even canon
 
rob
rob
And did you find the TOS-inspired animated series?
 
Slereah
Slereah
It was amusing
Especially when Spock summons the devil
Also for some reason there was a Kzinth episode
 
 
2 hours later…
user228700
5:13 AM
Hi, everyone :-)
 
user228700
I've a quick question for anybody who knows some inorganic chemistry.
 
user228700
We have:
 
user228700
$Al: [Ne]3s^2, 3p^1$ and $Mg: [Ne]3s^2$
 
user228700
Since the penetration of the $s-$ orbital is more than that of the $p-$ orbital, it becomes clear that the first ionization energy of Magnesium is greater than that of Aluminum.
 
user228700
The same argument must apply to $Si: [Me]3s^2, 3p^2$. However, we find that the first ionization enthalpy of $Si$ is higher. Is this because the increase in nuclear charge compensates for the reduced penetration of the $p-$ orbital?
 
2physics
2physics
5:41 AM
@JohnRennie : Hi. According your answer to this question, metals can't be used as an antenna in optical frequencies. But actually there is a type of antennas which operates in optical frequencies. How can it be explained then? Thankyou.
 
user228700
6:21 AM
@JohnRennie: Too busy with work these days?
 
John Rennie
John Rennie
@Kaumudi Morning. It's a bit busy this morning, but nothing too serious :-)
 
user228700
I see. Morning :-)
 
John Rennie
John Rennie
6:40 AM
@Kaumudi re your question about screening: the 3s orbital is closer to the nucleus that the 3p oribtal in some vague way that we're not going to fully define.
So you'd expect the 3p ionisation energy to be lower simply because the electron is farther away from the nucleus and therefore the magntiude of the electrostatic binding energy is smaller.
It isn't really a screening effect.
Now as you add elecrons to the 3p orbital the 3p electrons are all at the same distance from the nucleus, and they don't completely screen each other. So each successive 3p electron sees a slightly higher effective nuclear charge.
As a general rule, as you full an orbital the atom gets smaller and the ionisation energy increases.
 
user228700
7:04 AM
Oops, sorry, I'd gone to have lunch!
 
user246160
"A pump is required to lift 800 kg of water per minute from a 10 m deep well and eject it with a speed
of 20 m/s. The required power in watts of the pump will be ? "...can anyone here answer this question? I can calculate the work done to raise the water by 10 m but how do i take into account the work done to eject it with a velocity 20 m/s
 
DanielSank
DanielSank
I don't believe this.
 
user228700
Hmm, OK, it makes sense. Thank you :-)
 
DanielSank
DanielSank
I come home from work, get the mail, see an issue of Physics Today.
Warm up some leftover dinner (sausage and apples) and sit down at the table to eat and read a few articles.
I almost never do this. I usually toss those magazines in the trash immediately.
However, this evening, for some reason, I felt motivated to read a bit.
I open the magazine and browse the table of contents. Oh, neat! An article about artificial intelligence.
I start reading...
The article is about a research group that investigates an AI while it's running and learn things about the nature of consciousness.
Wow!
At some point the article mentions an AI mishap that occurred in 2096.
That's odd... that's in the future.
Then I realize this section of the magazine is a set of articles written as imagined in 2116.
They're all science fiction.
I was so mad that I flipped to the equipment advertisements and read about lock-in amplifiers.
@BernardMeurer @ACuriousMind @Danu you might find that amusing.
 
user246160
physics.stackexchange.com/questions/297096/… Can anyone here answer this question please ?
 
user246160
7:14 AM
0
Q: Power required by pump to lift water and eject it with certain velocity

TheStackExchange A pump is required to lift $m \space kg$ of water per minute from a $h$ metres deep well and eject it with a speed of $v \space ms^{-1}$. The required power in watts of the pump will be? The above question is from my textbook exercise. I have removed the numerical values from the origin...

homework-and-exercises newtonian-mechanics work power
 
user246160
Okay....I solved it now ^...nevermind
 
user246160
(deleted)
 
Swapnil Das
Swapnil Das
Indian Physics journals (with names Physics Today and Physics Spectrum) are mostly problem solving. It is sad that Indians seldom get a chance of experiencing the aesthetic side of physics.
 
user228700
7:46 AM
@JohnRennie: Halp! (Regarding s'thing other than phy/chem/math :-P)
 
John Rennie
John Rennie
@Kaumudi Yes?
 
user228700
You wake up pretty early, correct?
 
user228700
..?
 
John Rennie
John Rennie
Yes, generally about 5 a.m.
 
user228700
And dyou find yourself super sleepy at any other time of day?
 
John Rennie
John Rennie
7:51 AM
No. Not usually. Only after one of my giant weekend lunches :-)
 
user228700
:-P I see.
 
John Rennie
John Rennie
I have always had a tendency to insomnia, so I'm very disciplined in my sleeping habits. I always go to bed at 9 p.m. and I always wake at 5 a.m.
 
user228700
And for how long have u been waking up at this time?
 
John Rennie
John Rennie
If i start changing my sleeping time then I find I can't sleep and feel tired all day.
@Kaumudi Can't remember - years. Though when i was your age I would stay upmuch later and get up later.
 
user228700
Oh, I see.
 
user228700
7:54 AM
Years?! Well, that explains it, then.
 
John Rennie
John Rennie
It's not unusual for intensive studying to mess with your sleep cycle. Especially when you're doing it on your own as you are.
 
user228700
:-/ I see.
 
John Rennie
John Rennie
Studying under those circumstances is a surprising stressful thing to do. I suffered a bit in the last couple of months before my university finals.
 
user228700
Ohh, I see. Cambridge and all, so I imagine that it really was very stressful, eh?
 
John Rennie
John Rennie
I don't think there's a lot you can do about except try to relax as much as possible and bear in mind that it will be over soon ...
 
user228700
7:56 AM
Yes, I guess. Thank you :-)
 
John Rennie
John Rennie
@Kaumudi it's much easier when you're surrounded by your friends. You're certainly doing it the hard way!!
 
user228700
:-P Yeah, I can imagine.
 
John Rennie
John Rennie
I've currently got Star wars IV playing on your laptop to test the battery, and it's really good. You forget what a good film it is :-)
 
user228700
"My" laptop. Boy, that feels nice to hear :-D I dunno when I'll stop thanking u!
 
John Rennie
John Rennie
Obi Wan has just started teaching Luke how to use a light saber ...
 
user228700
8:00 AM
I dunno who either of those two people are :-P I promise to catch up next year!
 
Swapnil Das
Swapnil Das
@JohnRennie 9pm to 5 am is 8 hours. You're really disciplined.
 
DanielSank
DanielSank
@Kaumudi Star Wars
 
user228700
Yep, Ik that!
 
John Rennie
John Rennie
Now they're in the bar in Mos Eisley. Did Han shoot first?!!!
@SwapnilDas I have to be. If you have trouble sleeping then having a strict sleeping schedule is really important.
 
Swapnil Das
Swapnil Das
I see.
 
user228700
8:13 AM
@JohnRennie Who are u hoping will reply? :-P
 
John Rennie
John Rennie
Han shot first
"Han shot first" is a phrase referring to a controversial change made to a scene in Star Wars (1977), in which Han Solo (Harrison Ford) is confronted by the bounty hunter Greedo (Paul Blake) in the Mos Eisley cantina. The change was made for the 1997 Special Edition re-release of Star Wars, and has since been altered twice more. The phrase "Han shot first" is meant to express that "Han was the only one who shot", and is a colloquial retort to series creator George Lucas's explicit cinematic assertion that Greedo shot first. == Scene == Han Solo and Greedo both independently work for Jabba the...
 
Swapnil Das
Swapnil Das
My god, SW is a lot famous than I thought.
 
user228700
Ohh :-P
 
user228700
For anybody having a bad day, BTW:
 
user228700
 
Slereah
Slereah
8:18 AM
 
user228700
That ^ is the Nyan cat, whose body has been replaced by a NAND gate.
 
Slereah
Slereah
Ellis did a paper on singularity classification
 
Swapnil Das
Swapnil Das
@Slereah John Ellis?
 
Slereah
Slereah
Georges Ellis
 
Swapnil Das
Swapnil Das
Ohk.
 
Secret
Secret
8:23 AM
For me, most of my taking a test dreams are reflecting that I have obligations or responsibilities that I don't like and keep on procrastinating them, but it is getting more and more urgent to get them to finish. For example over the past months, I had a couple of dreams where I failed my english, chinese, maths, lab etc. tests and assignments. They can all be traced back to the fact that I keep procrstinating for my driver license test studying cause it is simply SO BORING but necessary
---
Falling teeth dreams often relates to my stress level
typo: peast=past
 
John Rennie
John Rennie
I dreamed I was a middle aged computer nerd - what a horrible nightmare :-)
 
DanielSank
DanielSank
@JohnRennie "dreamed"
 
John Rennie
John Rennie
@DanielSank I haven't woken up yet. This can't be real life, I mean, it's just too absurd :-)
 
DanielSank
DanielSank
 
user228700
@DanielSank x'D I think I've seen that one.
 
Secret
Secret
8:37 AM
[A bit old]
The power of electromagnetism, and yes there are physics there
 
user228700
@JohnRennie "Horrible"?! What about all the amazing stuff u can do now that u keep bragging (:-P) about?!
 
user228700
@JohnRennie: BTW, when was the last time u did this thing with the fixing and shipping a whole laptop and the whole "I am a God" (:-P) thing?
 
John Rennie
John Rennie
@Kaumudi when I was your age I was convinced I'd be the one to find a unified field theory (even though at your age I had no idea what that meant). It turned out to be harder than I thought ... :-)
When did I say I am God?
 
user228700
@JohnRennie Ah, don't we all think that? :-)
 
user228700
@JohnRennie You didn't. I chose to describe the situation like that. "When was the last time u shipped a laptop that u fixed to a person you've known for 3 months?" was my question :-)
 
John Rennie
John Rennie
8:42 AM
It's a fair cop
Jun 10 at 13:11, by John Rennie
General relativity, string theory and the WIN32 API. Truly I am a God like being.
 
user228700
Aha! :-P
 
Slereah
Slereah
@JohnRennie but society is to blame
 
John Rennie
John Rennie
I'm a victim of my upbringing.
 
user228700
Again, aren't we all?
 
Slereah
Slereah
Not me
 
John Rennie
John Rennie
8:44 AM
Reading science fiction during my formative years corrupted my brain and made me want to be a physicist.
 
user228700
^ I have to admit that I too have blamed Minutephysics on my difficult days.
 
John Rennie
John Rennie
ooh, ooh, they're in the trash compactor!!! They're going to die!
 
user228700
@JohnRennie :-P You are evading my question!!
 
Slereah
Slereah
Grand unified theories are so boring anyway
It's always some boring group theory thing
 
John Rennie
John Rennie
Hooray, R2-D2 saved them by hacking into the trash compactor and turning it off. See, computer nerds do have their uses!
 
Slereah
Slereah
8:47 AM
R2D2 is no nerd
He's a midget in a trashcan
 
John Rennie
John Rennie
A protocol droid
 
Secret
Secret
@JohnRennie I like GR, 80% because of time travel and alien spacetimes
 
Slereah
Slereah
That's C3PO
You pleb
 
John Rennie
John Rennie
I recently got told off for calling R2-D2 a robot.
 
user228700
-__- @JohnRennie Okay, u watch that movie and continue to evade my question.
 
Slereah
Slereah
8:48 AM
R2D2 would be a pretty bad protocol droid
He can't even talk
 
Secret
Secret
And I like particle physics, 80% because of chemistry+science fiction
 
John Rennie
John Rennie
I meant astromech droid. I knew that really!
 
Slereah
Slereah
C3PO is pretty much useless really
He uses his skills like once in the original trilogy
To talk to the ewoks
 
John Rennie
John Rennie
Why are the stormtroopers such terrible shots?
 
Slereah
Slereah
Narrative necessity
 
John Rennie
John Rennie
8:51 AM
Ooh, ooh, it's the duel between Obi Wan and Vader!!
 
Slereah
Slereah
Spoiler he dies
 
John Rennie
John Rennie
9:03 AM
@DavidZ I saw the original comment: stop ranting and answer the question. I wondered if anything had kicked off after that. While I wouldn't have posted the original comment myself I have to say I heartily agreed with it.
Watching Star Wars it's striking how grimy the settings are. I wonder if Ridley Scott was influenced by that when making Blade Runner.
 
user228700
@Slereah I'm 17. Haven't had the chance to watch it yet. Why u do this? :'-(
 
Slereah
Slereah
If you haven't watched it yet it is too old for you
You might as well look at a clay tablet
Go back to look at your fancy new movies that you youngsters watch
 
user228700
@Slereah This need not be true.
 
DanielSank
DanielSank
@JohnRennie are you watching ANH?
 
John Rennie
John Rennie
@Slereah the true SFF fan has read Gilgamesh in Sumerian on clay tablets :-)
 
DanielSank
DanielSank
9:12 AM
@JohnRennie yes, the dirt is much of why the movies were so good.
 
Slereah
Slereah
I have read the epic of gilgamesh
It's not a fun read
There's a lot of [LINE MISSING FROM TABLET]
 
John Rennie
John Rennie
@DanielSank 'Fraid so. I'm actually testing a laptop battery - by playing ANH - and of course I've got distracted into watching it.
 
user228700
How is playing the movie=testing battery? You're just gonna wait till it dies to check?
 
Ramanujan
Ramanujan
@Kaumudi hi
 
user228700
Hi :-)
 
John Rennie
John Rennie
9:16 AM
@Kaumudi It's a two hour film. I fully charge the battery, then play the film through, then see how much the battery charge has decreased. The battery should be good for four hours, so it should have 50% left when the film has ended.
 
user228700
Right :-)
 
Secret
Secret
Potato gun in slow mo
NB it is just pretty
 
Ramanujan
Ramanujan
Phenyl used incleaning is c6h5?
 
user228700
Wut?
 
koolman
koolman
Hii @JohnRennie
 
John Rennie
John Rennie
9:19 AM
The phenyl group is $C_6H_5$ i.e. a benzene ring ...
 
Secret
Secret
It appears there's something called a phenyl cleaner
Active ingredients to be look uped
 
Slereah
Slereah
So apparently a lot of the "computing quantum fields on curved spacetimes" papers use a dirty trick
They just use the conformal anomaly to shorten calculations
 
Ramanujan
Ramanujan
@JohnRennie same as google.co.in/… ?
 
koolman
koolman
 
John Rennie
John Rennie
@Secret phenyl disinfectant. It has phenol derivatives in.
 
koolman
koolman
9:21 AM
In this carnot cycle process how can we say net work = qh + qc
@JohnRennie
 
Secret
Secret
Yeah, they use some kind of pine oil extract, which has a lot of phenol and its derivatives
 
user228700
@koolman Did u read the transcript that I linked?
 
user228700
(Poor) JR and I have discussed this before.
 
koolman
koolman
Oh sorry I forget about it . @Kaumudi I will read it now
 
John Rennie
John Rennie
@koolman remember that a heat engine converts heat to work. It takes in a heat $Q_h$ from the hot source and releases heat $Q_c$ to the cold sink. The work done is the difference $Q_h - Q_c = W$.
That follows from conservation of energy.
 
user228700
9:23 AM
@JohnRennie: Let me know how the battery is :-)
 
John Rennie
John Rennie
Any moment, the film is just ending ...
 
koolman
koolman
@JohnRennie is there no work done in both adiabatic process
 
John Rennie
John Rennie
Work is $\int PdV$ so it is the area under the PV curve.
 
koolman
koolman
Yeah
 
John Rennie
John Rennie
@Kaumudi Wow, 69% remaining! That means you'd get a six hour battery life. Gosh, that's longer than I expected.
 
Slereah
Slereah
9:25 AM
Me I'm watching an intellectual movie
Gremlins 2
 
John Rennie
John Rennie
@Slereah Watch Sausage Party!
That is the no. 1 intellectual film of the year!
 
Slereah
Slereah
Sorry, too artsy for me
a real sausage kino
 
John Rennie
John Rennie
Actually I do recommend Sausage Party. It's exceedingly crude and does it's best to insult everyone. Hugely enjoyable :-)
 
user228700
@JohnRennie WOW!
 
user228700
Are u sure u wanna give it to me? :-P
 
John Rennie
John Rennie
9:30 AM
@Kaumudi Just as soon as I've swapped the screen :-)
 
user228700
:-) OK! Will u answer my question now, at least?
 
John Rennie
John Rennie
@Kaumudi you have mail
 
user228700
._. Why did u have to mail me that?
 
user228700
Huh. OK.
 
koolman
koolman
@DanielSank what is the name of book
 
user228700
9:39 AM
@koolman Dude, no. This:
 
user228700
Sep 15 at 7:00, by Kaumudi Harikumar
@JohnRennie Whenever you finish work, if u still feel like it/aren't too tired, I'm still kinda confused about the adiabatic process in that OK, I get that there is no way for the Carnot cycle to reverse without introducing an adiabatic expansion in b/w because otherwise, if we were to traverse back on the same isotherm, the work done by the engine would be zero which is not the type of engine anybody fancies exactly.
 
user228700
Scroll up and the conversation starts.
 
koolman
koolman
Ohk
 
user246160
0
Q: Is $W=\oint{\vec{F}.d\vec{r}}=0$ sufficient condition for conservative force?

TheStackExchangeI learned from my Physics textbooks that there is zero net work (W) done by the force when moving a particle through a trajectory that starts and ends in the same place i.e. $$W=\oint{\vec{F}.d\vec{r}}=0$$ Now, I need to verify whether the force $$\vec{F}=\dfrac{x \hat{i} + y \hat{j}}{(x^2+y^2)...

newtonian-mechanics classical-mechanics forces
 
user246160
Need help with this ^
 
DanielSank
DanielSank
10:06 AM
@koolman Statistical and Thermal Physics or something like that.
@JohnRennie the English are a silly people.
 
koolman
koolman
@DanielSank ohk I will see it If I have enough time
 
John Rennie
John Rennie
@DanielSank Have you seen Sausage Party?
 
user228700
10:23 AM
@JohnRennie Is it any good?
 
John Rennie
John Rennie
@Kaumudi It's kind of adolescent male humour. Whether you'd like it I'm not sure, though I'd guess probably not (you not being an adolescent male :-). But if you want a copy I might allegedly have a copy to hand.
 
user228700
> "It's kind of adolescent male humour."
 
user228700
Ah, that explains why u like it :-P (Jk)
 
user228700
No, no, never mind :-) I've asked for too many movies already :-P And also, me not being an adolescent male :-P
 
user228700
I've a quick question about vacuum and pressure and all...
 
John Rennie
John Rennie
10:29 AM
@Kaumudi Yes?
 
Mew
Mew
vacuum = empty
 
user228700
So there was this guy who connected two hemispheres and pumped out all the air and then couldn't separate them for the death of him?
 
John Rennie
John Rennie
@Mew mine's full of fluff and dust ...
@Kaumudi yes, the guy who hitched two teams of horses to try and pull them apart ...
 
user228700
Yeah, that guy :-P
 
user228700
What was the problem? What's going on, exactly?
 
John Rennie
John Rennie
10:31 AM
Magdeburg hemispheres
The Magdeburg hemispheres are a pair of large copper hemispheres, with mating rims. They were used to demonstrate the power of atmospheric pressure. When the rims were sealed with grease and the air was pumped out, the sphere contained a vacuum and could not be pulled apart by teams of horses. The Magdeburg hemispheres were designed by a German scientist and mayor of Magdeburg, Otto von Guericke, to demonstrate the air pump that he had invented, and the concept of atmospheric pressure. The first artificial vacuum had been produced a few years earlier by Evangelista Torricelli, and had inspired...
 
Mew
Mew
"mating rims"?
 
John Rennie
John Rennie
I love it when physicists talk dirty :-)
 
user228700
@JohnRennie ::reading...::
 
Mew
Mew
lol
 
user228700
Wow. Atmospheric pressure is huge is the point?
 
Mew
Mew
10:35 AM
atmospheric pressure doesn't change
yeah
atmospheric pressure is 1atm
 
John Rennie
John Rennie
101325 Newtons per square metre. That's ten tonnes per square metre.
 
Mew
Mew
Force required to pull apart = 1 atm * area
 
Physics Meta
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user228700
Yeah, that's a lot. This pressure thing is very confusing :-/
 
Mew
Mew
Pressure is just Force/Area
THink in terms of forces
it is the force that's important
Force = Pressure*Area
 
user228700
10:38 AM
Yeah yeah, Ik that, but OK, can u guys help me to figure this out:
 
Mew
Mew
.
._.
 
user228700
 
user228700
That first equation. How does that work!!?!
 
Mew
Mew
easy
follow the tube from left to right
starting from the left
we have the atmospheric pressure Pa pushing down
 
user228700
Yeah...
 
Mew
Mew
10:42 AM
now consider the line they've drawn
obviously the pressure in the beakar at that point equals the pressure of the tube at that point
otherwise there would be movement
 
user228700
Wait, gimme a second to process that.
 
user228700
OK, yeah, I guess that makes sense.
 
Mew
Mew
ok so temporarily I"ll introduce a new varaible Pt (tube pressure)
Pt = Pa + pgh1
agreed?
where Pt is the pressure at that first tube where the line intersects
this is because the pressure of the beaker where the line intersects is given by the atmosphere Pa plus the pressure due to the weight of the water above the line
sorry I meant Pt = Pa + pgh2
 
user228700
Oh God.
 
Mew
Mew
do u get it?
 
user228700
10:48 AM
One second.
 
Mew
Mew
Pt = pressure in the tube
pressure in tube = pressure in beaker at that point
pressure in beaker at that point = atmospheric pressure + pressure due to excess water
 
user228700
Wait!
 
user228700
Yes, all that makes sense...
 
Mew
Mew
ok
so now let Pt2 be the pressure in the second tube (at the line)
 
user228700
OK...
 
user228700
10:50 AM
Same story.
 
Mew
Mew
it should be clear that Pt = Pt2
 
user228700
It wasn't :-/
 
Mew
Mew
oh oops
ok
let's consider instead
the first tube
40cm up from the line
 
user228700
No no, wait!!!
 
Mew
Mew
and call this pt2
 
user228700
10:52 AM
I said it wasn't!
 
Mew
Mew
So let us say Pt2 is the pressure on the left most tube 40cm up from the line
 
user228700
Not isn't!!
 
Mew
Mew
?
 
user228700
I mean to say that it's clear now, but wasn't obvious before u explained it to me.
 
user228700
So in problems like these, I consider that the system is in equilibrium and basically just equate the force...but incorporate area and deal w/ pressure, yeah?
 
Mew
Mew
10:54 AM
wait
let's actually do this one ok?
 
user228700
I thought we were done with this?
 
Mew
Mew
so let us define Pt2 as the point in the FIRST tube 40cm upo from the mark
no
 
user228700
I understand it now! :-)
 
Mew
Mew
so you can derive the whole equation?
 
user228700
Yep!
 
Mew
Mew
10:55 AM
how
 
user228700
So $P_{t_1}$ should be equal to $P_{t_2}$
 
user228700
We have $P_{t_1}=P_a + \rho g h_1$
 
Mew
Mew
so how do you get the full equation tho?
 
user228700
One sec
 
user228700
And $P_{t_2} + 40 \rho g= P_a + \rho g h_2$
 
user228700
10:59 AM
And then we equate $P_{t_1}$ and $P_{t_2}$
 
user228700
Oh wait.
 
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