Mpemba effect

Crazy Buddy

Dec 3, 2013 01:19

None interested in Mpemba? Duh...

So, I did the experiment (somewhat okay-ish) on Sunday

At first, I took readings once every 10-15 mins or so...

Both cups are wholly identical, made of silver. I placed a thermocol below, in order to prevent non-uniform heating because the hot water may transfer the heat to the frost faster and may eventually get colder soon.

Brandon Enright

@CrazyBuddy Which experiment?

Crazy Buddy

@BrandonEnright Mpemba effect - I've been speaking about this for a long time..!!! :D

... Then, I placed a container (not lid) above the cups. So, heating takes place only by conduction via the metal. Whenever I take the readings, I take both cups out, measure the temperature and put both back in, at the same time.

Brandon Enright

Interesting.

I've only seen you talk about the wing size / speed thing recently.

Crazy Buddy

@BrandonEnright But, umm... it's home experiment. It didn't come out to be right. Hot water didn't freeze fast (I can't speculate a thing) :/

@BrandonEnright Yeah... Now, this one :P

Brandon Enright

@CrazyBuddy Reading wikipedia, it sounds like you should try to reproduce some of the describe circumstances

ManishEarth

Dec 3, 2013 01:29

@CrazyBuddy I have prettier plots!

Brandon Enright

@ManishEarth I love gnuplot :-)

ManishEarth

(band structure of graphene along an arbitrary circuit, just made it to test a procedure I wrote)

@BrandonEnright yeah!

Crazy Buddy

@ManishEarth What the???!!!! O_O

Awesome anyway... (though I dunno what that is...) :D

(continuing)...The next day, I had a guilt-feeling whether I had disturbed the system often by taking measurements every 10 mins. So, I did the experiment again, with water which was once boiled then cooled. Now, I measured every 30 mins and got more or less the same plot. o_O

Brandon Enright

@CrazyBuddy do you have a infrared (laser) thermometer?

Crazy Buddy

Brandon Enright

Dec 3, 2013 01:33

Also, do you have glassware?

Crazy Buddy

@BrandonEnright Nope... O_O

@BrandonEnright Like what? Spectacles? or lenses?

Brandon Enright

@CrazyBuddy beakers / conicals

@CrazyBuddy do you have some Amazon-like service easily available to you in India? Something that would sell laser thermometers and glassware?

Crazy Buddy

@BrandonEnright Nah... But, umm... won't beakers (after closing the lid) take too long to freeze?

Brandon Enright

@CrazyBuddy The listed explanations of the effect suggest it could have to do with convection / evaporation which means you shouldn't seal the container

Crazy Buddy

@BrandonEnright Even if we had, I'm not really in a nice condition to buy it :/

Brandon Enright

Dec 3, 2013 01:35

@CrazyBuddy I asked because I'd buy them for you if you did.

Crazy Buddy

@BrandonEnright Yeah, I read those... But, Physics FAQ looks nice ;-)

math.ucr.edu/home/baez/physics/General/hot_water.html

@BrandonEnright For that, I placed a tupperware container above, so that water wouldn't evaporate

Brandon Enright

@CrazyBuddy But it seems to me you should actually encourage evaporation

By, for example, adding acetone to the water

Crazy Buddy

@BrandonEnright OIC, so I should allow hot water to evaporate?

Then, it's obvious that the experiment would work... Right?

Brandon Enright

The suggestion that extensive evaporation of the hot water to reduce the volume is one way the effect works sounds very reasonable

@CrazyBuddy It still seems pretty non-obvious to me. One could totally imagine a case where anything you do to increase evaporation also delays freezing enough that it always loses

I think if I were to try to demonstrate the effect I'd heat one container of water to above the evaporation point of acetone and another to just below it and then add equal parts acetone to both

and then pop both in the freezer. I bet the hotter one will win

Crazy Buddy

@BrandonEnright Wait. Letting the hot water to evaporate (by not using any tupperwares above), the temperature can be easily reduced... Isn't that so?

@BrandonEnright That's cool..!!! Maybe, I'll try getting some acetone here :D

Brandon Enright

Dec 3, 2013 01:44

@CrazyBuddy Indeed it definitely reduces the temperature but at a cost of making it hotter. Which wins? The Mpemba effect claims suggest you can make the benefit of evaporation outweigh the drawback of the heat

@CrazyBuddy Very high proof alcohol could be almost as good a choice

Alright I need to go but it sounds like a fun experiment so you should keep posting about it as you try stuff :-)

Crazy Buddy

@BrandonEnright I will... Better I'll bookmark the conversation :D

For now, (till I do my next) the confusion is this...

Hot water, initially having a difference of more than twice that of cold water, at the final stage differs only by a degree...

How can both freeze at the same time? o_O

(... is exactly where my confusion lies)

@BrandonEnright BTW, regarding the IR laser thermometer, is it fast?

(reply when you come back)

For instance, my thermometer takes about 15-20 seconds to reach equilibrium :/

@ManishEarth: You have any suggestions?

Brandon Enright

Dec 3, 2013 02:36

@CrazyBuddy Instantaneous.

@CrazyBuddy You can see me use one in this video: youtube.com/watch?v=OVq1Phi2bTA

Anonymous

Dec 3, 2013 03:36

Is anybody there?

Brandon Enright

@Anonymous Yep

Anonymous

I have a quantum mechanics question, can you help?

Intro

Brandon Enright

@Anonymous To be honest, probably not but go ahead.

Anonymous

I'm just a little confused with singlet and triplet states, my professor said they related to the s and p orbitals in chemistry, but I'm not quite sure how-I thought p orbitals held 6, not 3 electrons...

Brandon Enright

@Anonymous Manishearth may be able to answer but you'd do better in the chemistry chat

Anonymous

Dec 3, 2013 03:45

Away I go~ Gracias

Wait the chem stack exchange is not nearly as lively

Crazy Buddy

Dec 3, 2013 03:56

@BrandonEnright I asked that because my thermometer is based on conduction (probably thermocouple I guess)

@BrandonEnright Hmm... I've subscribed to your channel somewhere in the past (but, haven't seen your videos) :D

Brandon Enright

@CrazyBuddy I don't actually fully understand how laser thermometers work and it's a question I've been meaning to ask on the main site

Crazy Buddy

Well, what do you do there?

@BrandonEnright Ask it away :D

Brandon Enright

@CrazyBuddy In the video I linked I get nylon very very hot with mineral oil

Crazy Buddy

@BrandonEnright No, not that... Generally, what do you do?

Brandon Enright

@CrazyBuddy Oh my official title is "Information Security Investigator" but what that really means is that I'm an information security professional and I specialize in incident response and forensics

Basically I'm on the defense side of hacking although I do spend a lot of time maintaining my offensive skills too.

Crazy Buddy

Dec 3, 2013 04:05

Oh... nice :)

Brandon Enright

I personally focus mostly on "big data" analysis, machine learning, and a bunch of math and statistics for sifting through large quantities of data

It's a pretty good job which allows me to pursue almost anything I want (within reason) for hobbies

Crazy Buddy

@BrandonEnright like what? NSA? :P

Brandon Enright

@CrazyBuddy No I work for a (very) big technology company and I focus on corporate security.

What the NSA does, doesn't surprise me but really pisses me off.

Crazy Buddy

Hehe :D

Looks like our Gamma-question got a nice revision :)

3

Q: Can one show that ${\gamma^5}^\dagger = \gamma^5$ directly from the anticommutation relations?

Is it possible to show that ${\gamma^5}^\dagger = \gamma^5$, where $$ \gamma^5 := i\gamma^0 \gamma^1 \gamma^2 \gamma^3,$$ using only the anticommutation relations between the $\gamma$ matrices, $$ \left\{\gamma^\mu,\,\gamma^\nu\right\}=2\eta^{\mu\nu}\,\mathbb{1},$$ and without using any specific ...

Brandon Enright

@CrazyBuddy Yeah I voted to reopen. It was a pretty good edit. We don't see a lot of those.

Crazy Buddy

Dec 3, 2013 04:11

Within 8 hours, I've been shot by two users for VTC'ing the question :D

Brandon Enright

@CrazyBuddy Shot?

Crazy Buddy

@BrandonEnright comments :)

one here, and one under one of my blog posts :D

user54412

Dec 3, 2013 04:28

@Anonymous the p orbital has total orbital angular momentum quantum number l=1, meaning it allows for 3 projected orbital angular momentum quantum numbers m=-1,0,+1...

user54412

...but the electron also has 2 spin "angular momentum" possibilities, and these are independent of the orbital numbers

Anonymous

But I thought they were called spin triplets?

user54412

@Anonymous yes, but everything doubles because wherever 1 electron is allowed, another with the opposite spin is also allowed

user54412

basically, the full state of an electron is the (tensor) product |position> x |l,m> x |s,sz>, and that last term gives the factor of 2

user54412

the middle term is the singlet for s-orbitals, triplet for p-orbitals, etc.

Crazy Buddy

Dec 3, 2013 04:51

Hiya @ChrisWhite :)

user54412

@CrazyBuddy Hi there

Crazy Buddy

Dec 3, 2013 05:07

sigh Internet disconnected...

@ChrisWhite So, have you selected your gravatar? Fast Chris..!!! Hatzz are coming :D

user54412

hmmm, I wonder if there are any galaxies that look good in hats

Crazy Buddy

You're still greenish... Even John Rennie has brought his facebook profile pic :D

@ChrisWhite Duh... Why? No faces? At least, select a comic face or something :P

BTW...

3 hours ago, by Crazy Buddy

How can both freeze at the same time? o_O

^^^ What do you think?

user54412

@CrazyBuddy well, they can't freeze at the same time, at least not if the masses of water are equal

user54412

but they can freeze arbitrarily close in time

Crazy Buddy

@ChrisWhite Can they?

user54412

Dec 3, 2013 05:18

well, if you put the samples in, say, a blast freezer, then they would both freeze quite quickly

Crazy Buddy

Wait.. I think I get it now. The curve is exponential. Right?

Newton's law of cooling

user54412

yep

Crazy Buddy

That the rate depends on the initial temperature... :D

@ChrisWhite Yay..!!! I get it.

user54412

your first graph seems a bit weird with the cooler sample - it looks linear rather than exponential

user54412

the second graph looks better

Crazy Buddy

Dec 3, 2013 05:21

@ChrisWhite Because, like I said, I disturbed them often -- I have to take readings, ya know :)

Open the freezer every 10 mins...

The hot water isn't affected much, because it's at higher temperature, while the cold water isn't... Right? :D

while the second one, I noted the values once every 30 mins :D

user54412

@CrazyBuddy that sounds right - if the ambient air in the freezer temporarily goes from, say, 28 F to 40 F, then T_cold - T_air is affected a lot, but T_hot - T_air isn't

user54412

and the time derivative of T_cold is proportional to T_cold-T_air

Crazy Buddy

@ChrisWhite Isn't it the other way around? T_hot-T_air is affected lot, while T_cold-T_air isn't? o_O

Or, am I confused? -_-

user54412

Suppose T_hot = 100 F and T_cold = 45 F, with T_air = 30 F. Then ΔT_hot = 70 F and ΔT_cold = 15 F. Now if T_air goes to 40 F, ΔT_hot becomes 60 F and ΔT_cold becomes 5 F. The hot water will cool at 60/70 it's original rate, while the cold water will cool at 5/15 its original rate.

user54412

hmmm, I just searched a term on wikipedia, and it took me to the hindi page rather than the english page

Crazy Buddy

Dec 3, 2013 05:35

@ChrisWhite Oh, I get it... I thought exactly the same - but got confused with the language :)

The h Bar

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