The h Bar

Kenshin

7:00 AM

this concludes my pitch

user228700

I'm up to speed about pressure not being everything. Don't jump to osmotic pressure from there!

Kenshin

@Kaumudi.H do you agree that water will flow from A to B due to diffusion

GPhys

I suppose at least a median must always exist

user228700

Yep.

Kenshin

this will increase the pressure in B

user228700

7:01 AM

Hydrostatic pressure, yeah.

Kenshin

now there are two competing forces causing movement

(1) diffusino from A to B

and (2) pressure from B to A

user228700

Right. This pressure and the entropy wanting to increase.

Kenshin

when the flow of water from (1) A to B balances (2) B to A we are at equillibrium

user228700

Right...

Kenshin

and at this equillibrium, we know that the pressure of B is greater than A

we call this pressure difference , the "osmotic pressure"

so we can think of (1) being the osmotic presure which balances (2) the hydrostatic pressure difference at equillibirum

user228700

7:03 AM

It's a little difficult for me to fully digest the fact that the system eventually attains equilibrium despite these opposing tendencies.

Kenshin

@Kaumudi.H well as the pressure in B gets bigger, it causes water to flow from B to A

and the concentrationi difference always causes water to flow from A to B

eventually as B gets more wate,r the flow from B to A matches the flow from A to B

user228700

@Kenshin What, what, what? Isn't the pressure difference the hydrostatic pressure?

Kenshin

and then the system is in "dynamic" equillibrium

@Kaumudi.H yes the hydrostatic difference = osmotic pressure, they balance

user228700

Yeah, I guess that does make sense, but still. Okay.

user228700

@Kenshin Wut? O_o They're not the same?

Kenshin

7:05 AM

@Kaumudi.H well at equillibrum the hydrostatic pressure in B exceeds A correct?

let's call this difference x

x = hydrostatic pressure difference ( by definiition)

user228700

OK...

Kenshin

and we define osmotic pressure to be the hydrostatic pressure difference at equillibrium

user228700

Okay. But they don't balance, no? It's just hydrostatic pressure known by a different name, no?

Kenshin

@Kaumudi.H we say that "osmotic pressure" from A to B, balances the "hydrostatic pressure from B to A

@Kaumudi.H let's think just prior to equillibrium when these are not equal

e.g. at time 0, the hydrostatic pressures are not 0

but water is flowing from A to B

user228700

So whatever this entropy driven process is, that's causing the osmotic pressure, u mean?

Kenshin

7:08 AM

@Kaumudi.H osmotic pressure is a "fictitious pressure" given to describe the entropy driven process

so we can say that at time 0, water is flowing from A to B due to "osmotic pressure"

at equillibrium, the hydrostatic pressure from B to A, balances this "osmotic pressure" from A to B

user228700

Exactly, that's what I meant to ask. Okay, I think it's clear now.

Kenshin

cool

user228700

@JohnRennie: Dyou have anything to add..?

John Rennie

Is it my turn?

Kenshin

@JohnRennie yes it is :)

user228700

7:10 AM

Yeah. I mean, I understood and all. So I don't think I need u to explain all over again...

John Rennie

@Kaumudi.H Ok

user228700

I was just wondering if u have anything to add to the discussion "Kenshin" and I just had..? (@Kenshin: Seriously, it's really weird, switching for "Mew" to "Kenshin" now. What is your real name? O_o)

John Rennie

I think there's a simpler way of looking at it ...

Kenshin

@Kaumudi.H my real name is a secret

user228700

@JohnRennie OK...

user228700

7:13 AM

@Kenshin Sure, sure, 'cause u may be the prime minister of Australia -__-

John Rennie

The pressure on a surface is proportional to the number of molecules per second hitting that surface and bouncing off it.

Kenshin

lol

user228700

Yeah...

John Rennie

Suppose there is some probability P that a molecule hitting the surface will go through it instead of bouncing off, then the number of molecules per second that pass through the surface is the number hitting the surface per second times the probability P.

Kenshin

I thought you said simpler

user228700

7:16 AM

^ x'D Yeah.

user228700

@JohnRennie OK...

John Rennie

So the flow rate through the surface is proportional to the pressure times the probability.

user228700

:-| Okay...

John Rennie

On one side we have pure water at a pressure of 1 atmosphere so the flow rate will be proportional to 1P.

Kenshin

@JohnRennie I see where you're going that's a good explanation too

user228700

7:17 AM

Uh huh...

John Rennie

On the other side we have a mixture of water and sugar. The total pressure is 1 atm i.e. the partial pressure of the water + the partial pressure of the sugar = 1. So the partial pressure of the water must be less than one.

user228700

Yeah...

John Rennie

Let's say the partial pressure of the water is 0.5 atm just to choose a figure, then by the same argument as before the flow rate through the membrane will be 0.5P.

(I really shouldn't have chosen P for the probability as it's confusing with pressure!)

With me so far?

user228700

U really shouldn't have but OK...

Kenshin

@JohnRennie so basically water flows from the pure water side to the solution side?

John Rennie

7:21 AM

So we have a flow rate of 1P from water into the solution and a flow rate of 0.5P from the solution into the water.

And there is a net flow rate of 0.5P from the pure water side to the solution side.

user228700

Yeah, OK...

John Rennie

OK. Now I leave the pressure at 1atm on the water side ...

And I increase the pressure to 2 atm on the solution side.

user228700

Uh, OK...

John Rennie

So on the solution side the partial pressure of the water + the partial pressure of the sugar is 2 atm.

user228700

It flows the other way, yeah?

John Rennie

7:24 AM

And if I assume the partial pressures are still equal that means the partial pressure of the water on the solutuion side is now 1atm.

So the flow rate from the solution side to the pure water side is now 1P.

user228700

Ohh.

user228700

So the flow stops.

Kenshin

@Kaumudi.H the NET flow stops

John Rennie

And we have a flow rate of 1P from the water to sugar side and a flow rate of 1P from the sugar to water side.

Kenshin

it's called a "dynamic" equillibrium

there is always flow back and forth, but the net flow is 0

user228700

7:26 AM

Yeah, OK...

John Rennie

By applying an external pressure to the sugar side I have stopped the net flow.

user228700

Yup. Okay...

user228700

And this is not equilibrium?

Kenshin

it is equiillbrium

a type of equillibrium known as "dynamic" equillibrium, (the most commmon type of equillbrium when dealing with solutions etc.)

user228700

But but but...

Kenshin

7:28 AM

there is flow of water to the left and to the right, but if they equal you don't really notice either compartment changing

John Rennie

@Kaumudi.H we need to be a bit careful about what we mean by the word equilibrium

user228700

Oh, right, okay...

111

Hi, people. :)

user228700

Yeah, okay, I think I understand now...

user228700

Alrighty, thanks, you guys :-D _/\ _

Kenshin

7:28 AM

np

John Rennie

@111 hi

Kenshin

this topic is very important for understanding how brain cells (neurons) work

koolman

@Kenshin why name changed

user228700

^ Not into Bio

111

Okay, john. I'm @AakashTomar. :P

Kenshin

7:30 AM

@koolman cos i like this name better now

John Rennie

Aha! Hi Aakash.

koolman

Oh , what your's real name @Kenshin

Kenshin

@koolman what's yours?

koolman

Koolman

Kenshin

serious?

111

7:31 AM

What is the subject for the discussion today? Something a highschooler can comprehend?

Kenshin

@111 the topic is osmosis

highschoolers likely can't comprehend it

koolman

What yours @Kenshin

111

Well, I know the basics.

But yes, not the details.

Kenshin

@koolman it's a secret

@111 yes it's a battle between the second law of thermodynamics and hydrostatic pressure

John Rennie

@Kaumudi.H the Test match is in Chennai this weekend

user246160

7:33 AM

@111 Hi, where are you from ? :)

Kenshin

and is essnential for the neuronal action potential

111

I'm from India. @Doraemonドラえもん

user246160

@111 State ? City ? I'm from West Bengal.

Kenshin

without osmosis we would never even be able to comprehend osmosis

koolman

@Kenshin where are you from

111

7:34 AM

Well, I'd like to know your location first. I don't divulge extremely personal details over the internet.

Kenshin

@koolman Australia

koolman

Oh nice

111

So you folks are debating on the validity of the second law in the case of osmosis?

user246160

@111 Don't worry. No one can track you only using your city :P

111

I've done a bit of fluid dynamics, so maybe I could add something.

Doraemon, tell me your state and I'll give you mine.

user246160

7:36 AM

@111 I already told you my state

user246160

See above

111

Oh, okay. I'm from Delhi NCR.

user228700

@JohnRennie Don't follow cricket, sorry :-|

koolman

@111 in delhi where ???

user246160

Oh nice :)...class 12 ? @111

Kenshin

7:37 AM

@111 no not a debate we were explaining how osmosis works. The process of osmosis involves the competition between increasing entropy battling against hydrostatic presusre

user228700

@Doraemonドラえもん Dude, u're obsessed :-P

111

Yes. Class 12.

Kenshin

but this topic has been done

@111 what career do you want?

111

Oh, alright @Kenshin.

user228700

@Kenshin U as well :-P

Kenshin

7:38 AM

@Kaumudi.H what do you mean, I have a career

oh u mean i'm obssessed

user246160

@Kaumudi.H I am surprised actually at the number of Indians on SE...where are Russians, Chinese and people from Middle East ? The population here is sooooo skewed !

Kenshin

yea dood

@Doraemonドラえもん that's racist

111

@Doraemonドラえもん I want to be an entrepreneur, but there's a long way, I don't have any quality of an entrepreneur. But I want to start a physics related venture.

user246160

@Kenshin What the hell ?

Kenshin

jokes

but you know russians speak russia, chinese speak mandarin etc., middle east speak middle east

user228700

7:39 AM

@Kenshin Yup. With people's careers :-P

Kenshin

but indians speak english

John Rennie

@Kaumudi.H just as well. The English team isn't doing well.

user228700

:-P I see.

Kenshin

@Kaumudi.H yeah because careers make up alot of people's lives

user246160

I am asking the reason for the skewed population ratio on Stack Exchange and it is surprising that I find only people from Europe, America and India

user246160

7:40 AM

@Kenshin In those countries too english is a second language and so is it in my country

koolman

@Doraemonドラえもん because most of us speak english

Kenshin

@Doraemonドラえもん no @Kaumudi.H says that englihs is a national language of india

user246160

@Kenshin No. It is just an official language and a second language for most.

koolman

@Kenshin but not in day to day life

user246160

Hindi and English are the two official languages but for 99 percent people english is a second language

Kenshin

7:42 AM

but i think more indians know english than chinese do though?

same with Russia

user246160

@Kenshin Why do you think so ? I am curious

Kenshin

@Doraemonドラえもん lemme look up some stats

apparantly 10% of the popuation of india know english

now let me see for russia and china

also note china has internet restrictions which could be why we see less of them

not sure exactly how they are restricted tho

user246160

@Kenshin point!

user246160

china has restricted fb too

user246160

i guess

Kenshin

7:47 AM

for china, according to quora, "That’s less than 1% of the population (the second lowest percentage of English speakers out of all countries in the world)"

so Chinese apparantly don't know english as well as India

now for russia

8% of Russians who can "speak" English.

again according to quora

so India tops the list in % of english speakers, and has the second highest world poopuation

so this is why we see lots of people form india

user246160

Apparently there are 2 people from Europe - JR and ACM in the chat room. 3 people - Heather, Daniel and Dmckee from US, G.bergeon from Canada, and 6 people from India....so I get it now....it is because of the high population, and that dominates the fact that only 10 percent people know english

user246160

good fact :)

user246160

Oh I think DavidZ is from China :)

Kenshin

yeah like 10% of india's population is nearly 50% of USA popualation

user246160

No one from Russia and Middle East over here !

user246160

7:51 AM

And you from Australia

Kenshin

yeah russia has half the population fo the USA, and only 8% of russians speak english so not many

user246160

Is English the national language in Australia ?

Kenshin

yeah

user246160

i see

Kenshin

that's our only language

(but we have many people born overseas )

user246160

7:57 AM

I hope in the future someone invents a good translator app that will allow all people to use Stack Exchange without worrying about language!

user246160

Google Translate is not so effective though.

Kenshin

No but I think it will get better

user246160

yep..i hope

111

Sorry guys, had to go for lunch.

user246160

@111 you are in 12...so will you give the engineering exams ?

user246160

8:08 AM

or will you go for mainstream physics courses ?

111

Of course I will. But not JEE Advanced, I'm too dumb and unprepared to crack it.

I'm particularly interested in Engineering Physics.

user246160

@111 I hate it when people call themselves dumb. BTW without giving JEE advanced how will you get in Engineering Physics ? Only IITs provide that subject I think

111

@JohnRennie What do you think about Engineering physics? Worth it?

Nope, few NIT's too.

John Rennie

@111 I can't comment. As a general rule you will do best at things you enjoy doing.

111

Dumb=10% , Lazy and unprepared = 90%.

Of course. Right, John. But I was wondering what is the stuff those guys do.

By the way, see this. Really cool.

upload.wikimedia.org/wikipedia/commons/f/f4/…

user246160

8:13 AM

Engineering Physics is same as an applied physics degree with some coding experience and some stuff added from electrical and electronics

Kenshin

sounds like a fad

engineering is physics

user246160

The only advantage is that you can complete engineering physics in 4 years and directly apply for a combined MS+PHD degree

user246160

Applied physics is a 5 year course

111

Well, for now, I'll be content if I get it in any college.

user246160

hmm

Kenshin

8:17 AM

Why don't you study computer science?

111

That video uses something really complex called meissner effect. I mean, it says something about superconductors expelling magnetic fields during transition, that's all I can understand.

Kenshin

I think computers will be a big industry in the future

111

@Kenshin Simple, I don't like it. And I don't wanna be the hero of uncles and aunties.

Kenshin

what do you mean hero of uncles and aunties?

111

You did not get the sarcasm. Never mind.

Kenshin

8:19 AM

Probably cutlure joke I don't understand in Australia

111

Yes, exactly, it's a culture joke.

Kenshin

yeah I don't understand

what does it mean "hero of uncles and aunties"

user246160

@Kenshin Every second person in India wants to be a coder due to the high paying jobs :P

Kenshin

oh k

ty @Doraemonドラえもん

111

Thanks, doraemon.

user246160

8:20 AM

And everyone in the family forces them to take coding :P

Kenshin

in Australia it's doctor they want to be which pays the highest

user246160

Welcome :)

user246160

@Kenshin even in india :D

user246160

doctor or coder!

111

Those two are the perfect cheese for the mice.

user246160

8:21 AM

Its sooooo boring and irritating at times....fortunately my parents never forced me

user246160

:P

Kenshin

I think anyone interested in physics should learn coding

111

My parents never do that too.

Kenshin

coding, like maths, is a great tool for analysing the world

user246160

@Kenshin Yes, I agree :)

111

8:22 AM

Of course Kenshin. I'm into some Python and Ruby for now.

But they are merely tools. I don't want a living out of them.

Kenshin

@111 it is privledge to enjoy how to make your living

but if you can find something you enjoy which you can earn a living from, you should do it

111

It's a matter of choice. The first few years, you face rants and taunts for not choosing the better path, but after that everyone stops caring. Plus, you have to struggle for the, say, 10 years (initial), you may even go broke in those 10.

Kenshin

Yeah going broke doesn't sound like fun

you must find balance between income and pleasure

don't seek income alone, don't seek enjoyment alone (you need moderation in both to be happy)

111

Exactly.

Tesla did not know this balance, Edison did. P

:P

Kenshin

indeed

111

8:31 AM

Doraemon, are you in IIT right now?

Just guessing.

user246160

@111 No I am in 12th. Want to be there next year :).

user246160

ManishEarth is from IIT Bombay here.

user246160

He is a moderator

111

Oh, great.

IIT-B requires a great deal of sacrifice on the student's part.

user246160

The sacrifices are justified by the returns you get :)

111

8:35 AM

Indeed. Cannot agree more. IIT's have the best research environment in India.

For my part, I think the farthest I can reach is DTU engineering physics.

user246160

Yes. Bye. I gotta go now :)

user246160

Nice to meet you

user246160

Tata!

koolman

8:55 AM

@Doraemonドラえもん who is manishearth

Secret

9:29 AM

A New History for Humanity – The Human Era

►

koolman

9:54 AM

@Kenshin are you there

Kenshin

10:08 AM

yeah

koolman

@Kenshin see this

physics.qandaexchange.com/?qa=514/…

Kenshin

not bad

I see you state "then we hqve to find the value of U/W"

koolman

If it is ok then please open it

Kenshin

but you haven't defined what U and W are

you should say, where U is .... and W is ....

koolman

@Kenshin they are common terms

Kenshin

10:13 AM

while W is likely work, you should still define it because W can mean anything

koolman

If neccesary i will do it

Kenshin

@koolman I've done a physics degree and I've used W to represent many different quantities. We learn that is always correct practise to define your symbnols

Please define U and W and i'll reope

koolman

Done :)

Kenshin

very good thankyou for putting in the effort to improve this question

i've reopened

koolman

Thank you @Kenshin

I will do for rest later

Got some work ,tal to you later

Bye

Kenshin

10:17 AM

laterz

Slereah

10:39 AM

@ACuriousMind

user116211

12:10 PM

0

Q: Shape of planetary orbits

Why is Venus' orbit almost circular, though mercury's highly elliptical? Further, Why is mercury's orbit most elliptical right after Pluto?

user116211

Insufficient research efforts?

user246160

2:32 PM

Manishearth ♦, Berkeley, CA, United States

14.8k 4 38 87

homework-and-exercises newtonian-mechanics forces electromagnetism electrostatics energy thermodynamics

heather

@Doraemonドラえもん, hello

user246160

@heather Holla :D

user246160

@Ramanujan Were you able to solve the exradii problem ?

Ramanujan

@Doraemonドラえもん yeah,dhmo showed how to solve

user246160

@Ramanujan Oh, good :)

Ramanujan

2:39 PM

@Doraemonドラえもん did you remembered all inverse trigonometry formulae?

user246160

@Ramanujan Yes, most of them I do. But I find the formulae involving solutions of triangles difficult to remember. Inverse trigo is easy once you are able to derive all the formulae by yourself.

Ramanujan