The h Bar

Kenshin

11:00 AM

is that your bank balance?

user228700

My bank balance? Oh, that's less than £2.

Kenshin

then what's 57?

it's very specific

G. Bergeron

@Kenshin Same price for those here, but is that really what you call a good laptop? Gaming computers are known to be really expensive, especially in the laptop format. I never needed a robust GPU

user228700

Yes, £57 = Rs. 5000

Kenshin

oh

@G.Bergeron yeah they're probably overpriced

G. Bergeron

11:02 AM

I don't like british pounds, they make me ruin myself when there. Same for swiss franc

Kenshin

@G.Bergeron I perosnally prefer a desktop because I find all laptops are too slow or have heating issues

G. Bergeron

@Kenshin ? Slow?

user228700

My parents are paying for this. I'm totally broke. I have enough to treat myself to some pastries, perhaps.

Kenshin

YEah a good desktop outperforms the best laptops

G. Bergeron

@Kenshin What are you doing with your computer?

Kenshin

11:03 AM

In the past I've run very large simulations in R

G. Bergeron

@Kaumudi.H Isn't this normal at that point in life?

user228700

@G.Bergeron I sure hope so :-P

G. Bergeron

@Kenshin I don't know I've always used apple computers and I know I'm never doing heavy simulations but never had problem besides RAM with 200+ tabs open in different browsers...

Kenshin

yeah my simluation needed more RAM

I've never used apple though

G. Bergeron

I'm looking into buying GPUs to do computing now, for personal use

@Kenshin We had them when I was a child and they where gray and I guess it sticked with me

@Kenshin For desktops with apple, you pay a bit too much for the brand, but I think the air line is still competitive

Kenshin

11:06 AM

I agree, I think apple desktop would be overpriced

But most dekstops are alot cheaper than laptops for the RAM and performance

You pay more for the portability of the laptop

G. Bergeron

And you get a nice wrapper for unix (os x) but were I to get a desktop, I would just buy components.

Kenshin

to fit all of that stuff in a smaller space

G. Bergeron

@Kenshin And the battery

Kenshin

exactly

G. Bergeron

But I like laptops!

Kenshin

11:07 AM

so cos I do all of my computing at home, I prefer to use all my money for performance rather than portability

G. Bergeron

@Kenshin I can understand, I just never really need the performance

Kenshin

yeah laptops are cooler

koolman

Can I ask my physics doubt ?

Kenshin

@koolman why don't you post it to physics.qandaexchange.com

G. Bergeron

yes

@Kenshin Isn't that for homeworks?

Kenshin

11:09 AM

yes

koolman

@Kenshin I have already posted , now I have a conceptual problem in that

Kenshin

alright @koolman what do you doubt?

G. Bergeron

In any case, going back to work... Good luck with the delivery @Kaumudi.H

koolman

Does kinetic friction does not apply when object rolls without slipping

Kenshin

no that's static friction

@koolman when you walk, it is static friction that pushes you forward do you agree?

because each foot is static with the ground

koolman

11:12 AM

It will reduce the linear acceleration

@Kenshin yes

Kenshin

Similarly with a rolling object, the point in contact with the ground is statically pushing back on the ground

just like in walking

it isn't "scraping" along the ground

koolman

So it will not affect linear acceleration @Kenshin

Kenshin

Basically rolling is just another form of walking, but if you had infinite legs and stepped very quickly

koolman

@Kenshin what about linear acceleration

Kenshin

@koolman it won't affect linear acceleration

koolman

11:19 AM

Why

Kenshin

@koolman this has a good explanation:

lhup.edu/~dsimanek/scenario/rolling.htm

koolman

Ok let me see

Kenshin

wait

@koolman it may not be the best

anyway

basically

why would it slow down?

the friction is static

does the ground slow you down when you run? No

the friction actually helps the ball roll

koolman

@Kenshin it increases its angular acceleration

Kenshin

what?

koolman

11:22 AM

@Kenshin en.m.wikipedia.org/wiki/Angular_acceleration

user228700

@G.Bergeron Thanks :-)

Kenshin

I know what angular acceleration is

user228700

x'D Poor @Kenshin

koolman

@Kenshin then due to friction will it increase

Due to torque

Kenshin

what do you think

koolman

11:26 AM

Increase

Kenshin

and what do you think happens if angular accelartion increases?

koolman

More fast rolling

Kenshin

is this what you observe in real life?

that a ball continues to get faster forever?

koolman

Ah no

But there will be torque

Kenshin

will there be torque?

let's Imagine we release a ball with translational velocity of $v$

but let's suppose the ball has no rotational velocity

this means the object will slide correct?

in this scenario, there will be kinetic friction

that causes the ball to rotate

this will continue to apply to the ball

koolman

11:31 AM

Yes

Kenshin

until the ball is rotating such that the tangential velocity is equal to the translational velocity

koolman

Yes

Kenshin

but note the translational velocity is in the opposite direction to the tangential velocity

this means that the point of the object in contact with the ground actually has a velocity of 0

koolman

Yeah

Pure rolling

Kenshin

so what torque do you think will be generated when an object with velocity 0 (the ball) touches another object with velocity 0 (the ground)?

koolman

11:33 AM

But if a body rolls on an incline plane

Kenshin

this is new, you never stated we were on an incline plane before

but go on

koolman

I forget that

physics.qandaexchange.com/?qa=619/ratio-of-acceleration

@Kenshin then there will be torque

Kenshin

indeed

and as the answer states, presumably the balls wont' slip,

koolman

@Kenshin torque cannot be from gravity

Force due to gravity is at its centre of mass

4

Q: Ball Rolling Down An Inclined Plane - Where does the torque come from?

There is a ball rolling down an incline, with no slipping. If we consider the point of contact between the ball and the inclined plane to be the pivot point (for our torque calculations), then I have noticed that friction is no longer in play, and gravity (and normal force) is the reason for the ...

Kenshin

yeah that answer explains it well

koolman

11:40 AM

So angular acceleration is increasing

Kenshin

when rolling down the hill, of course

koolman

Yeah

Thanks @Kenshin

Kenshin

np

koolman

@Kenshin on inclined plane also there will be no kinetic friction

Kenshin

correct, there will only be kinetic friction if there is "slipping"

which you would ordinarily assume there isn't, becuase if there was it would quickly accelerate the system back to equillibrium again

kind of like the example I gave with teh ball of velocity $v$ and no rotation, given enough time the torque due to slipping will force the ball back to the rolling state

koolman

11:43 AM

Yeah :-)

Kenshin

@koolman good question btw on the site with ur attempt shown

koolman

Thanks

koolman

11:56 AM

@Kenshin what should I do to this question physics.qandaexchange.com/?qa=618/angle-turned-by-disk

Sammy has explained me in comments

Kenshin

just leave it

the comments may help someone else in the future

and maybe someone will come and answer it one day which would help others even more

koolman

Ohk

@Kenshin Actually I have edited with answer

Kenshin

no don't do that

that's confusing

but you can answer your own question in the "answer" section

koolman

Then

Kenshin

I think you should leave the question as it was, and then just add your answer in the answer section

koolman

11:59 AM

@Kenshin but in that answer sammy helped me so he should add the answer

Should I message him

up to you dood

Ohk

Hi

hi

I earned a secret hat

Secret

news.nationalgeographic.com/2016/12/…

Kenshin

12:13 PM

wow

that's awesome

my fasvourite is the klingon Newt

the rainbow serpant has shrunk alot since the time of the aborigines

John Rennie

What was the "where are you hat" for? Did it tell you when you got it?

Something to do with your location in the world I guess ...

Kenshin

@JohnRennie it says it's a secret hat

John Rennie

So it didn't say why it was awarded to you?

heather

hello

Kenshin

nope

AccidentalFourierTransform

12:18 PM

@JohnRennie I got a secret hat too, no idea why

Kenshin

But I got it shortly after closing a few questions

I tried to close a few questions to get the abominable hat

and I got this one with it

Maybe it's for getting 2 hats after 10PM or something

AccidentalFourierTransform

I posted an answer to a question which already had several answers

Kenshin

after 10PM?

AccidentalFourierTransform

and then upvoted several answers in the same question (different question than before)

Kenshin

I didn't do any of that

@AccidentalFourierTransform what country areyou in?

AccidentalFourierTransform

12:21 PM

My hat is different than yours though

Kenshin

oh

AccidentalFourierTransform

its past 13.00 here, in Spain

Kenshin

it's irrelevant i thought you had the same hat lol

Swapnil Das

People get addicted for hats.

AccidentalFourierTransform

yeah, it is fun for some reason

Kenshin

12:22 PM

yeah cos they're awesome

Swapnil Das

Agreed.

@AccidentalFourierTransform You are a physics Graduate?

AccidentalFourierTransform

@SwapnilDas kind of, yes

I graduated recently, I dont have the official certificate yet

Kenshin

doesn't count then

AccidentalFourierTransform

lol ;-)

Swapnil Das

:P

heather

12:24 PM

totally counts

@AccidentalFourierTransform, congratulations!

Kenshin

na the certificate is everything

I bought my certificate online

AccidentalFourierTransform

@heather thanks :D

heather

0

Q: Perturbation Theory for a ring in an Electric Field

particle pf mass m move on a circular ring of radius a.The only variable of the system is the azimuthal angle, which we will call .The state of the system is described by a wave function ψ(φ) that must be periodic. ψ(φ + 2π) = ψ(φ) and normolaized. Now assume that the particle has a charge q an...

quantum-mechanics

Swapnil Das

@Kenshin Ok bro calm down :P

heather

^thoughts on this question?

Kenshin

12:25 PM

@heather i'd close it but I already have my abominable hat

Swapnil Das

@AccidentalFourierTransform Would you mind telling your specialization?

Kenshin

anyone else seen rogue one?

AccidentalFourierTransform

@SwapnilDas I'm studying theoretical physics.

Swapnil Das

@AccidentalFourierTransform Great. Even more specially (Like, string theory, Stat Mech. or GR)?

Kenshin

let me guess

condensed matter/statmech

Swapnil Das

12:28 PM

My guess is GR/mathematical physics.

AccidentalFourierTransform

@SwapnilDas I'm not much into GR. I like quantum field theory.

@Kenshin oh no, not at all :P

Kenshin

I just guessed the most popular branch of theoretical physics

Swapnil Das

I won (mathematical physics) !

Kenshin

no QFT <> mathematical physics

Swapnil Das

Most popular, seriously?

Kenshin

12:30 PM

as in, the one where most people work

not necessarily the one most people like

heather

i just earned a secret hat!

Swapnil Das

Oh. Then fine.

Kenshin

Good Job Heather

which one, same one asme?

Swapnil Das

@heather Yohoo!

heather

same as accidental fourier transform's

should be showing up in a minute

Kenshin

12:31 PM

oh yeah, that's the opposite one of mine

I think it's to do with the December solstice

heather

i did a couple of close vote reviews, then a low quality review, and got the hat =)

Swapnil Das

Do hats show up to the user himself?

Kenshin

and what hemisphere you dwell int

if you're in the North hemisphere you get heather's hat

if you're in the South hemisphere you get my hat

heather

right...

the hat is called "where in the world"

so

Swapnil Das

I wonder what drives so many guys towards condensed matter

Kenshin

12:32 PM

mine is also called "where in the world"

@SwapnilDas because it's easier to find new stuff to work on

there are more unanswered questions in condensed matter than other branches

Swapnil Das

Umm.

heather

umm

no. just no.

Swapnil Das

Not in GR, strings, QFT and so?

Kenshin

no, it's much harder to make a contribution there

GR is pretty well defined

The standard model is also pretty good

String theory is questionable science

We are waiting on a breakthrough

heather

uh...standard model is not complete!

Kenshin

12:35 PM

but breakthrough's are hard, so people prefer condensed matter

heather

quantum gravity! TOE!

but....

there are so many things that bother me here.

Kenshin

in the "publish or perish" culture, most perish when doing quantum gravity

Swapnil Das

Hmm.

Kenshin

@heather there's definitely questions to answer, but they are harder to answer

heather

how 'bout quantum computing!

Kenshin

12:36 PM

condensed matter is easier because it is more applied

heather

oh, yay, new hat showed up

Kenshin

YEs quantum computing is going tob e more popular in the future

Swapnil Das

But yeah, great minds do physics for revolutions, not papers :)

heather

::winces::

Kenshin

but yes definitely lots of room for physicists to work in quantum computing which definitely overlaps statistical mechanics

@SwapnilDas yes but most physicists after age 30 just want a stable job

heather

12:37 PM

i think what makes me extra interested in quantum computing is it is at the intersection of physics, math, computer science, and engineering, aka, all my interests. =)

though of course it's just interesting.

Kenshin

Yeah I think your the perfect age to contribute to it

AccidentalFourierTransform

@heather wait. Are you actually 13?

heather

@AccidentalFourierTransform, year older, but yeah.

8th grade.

Kenshin

You'll be in uni when QM Computing will be expanding rapidly which is great

heather

oh, okay

Kenshin

12:38 PM

well it's very early days right now

heather

sure.

Kenshin

but there will be more investment into it soon I believ

AccidentalFourierTransform

@heather that is impressive, congratulations :-)

you'll be a very successful scientist some day

Kenshin

@heather yes congratulations for being in 8th grade

Swapnil Das

Heather is obviously talented.

Kenshin

12:41 PM

you don't know how old she is though?

maybe she was kept back several years

heather

@Kenshin, i assure you i was not.

Kenshin

oh

heather

@AccidentalFourierTransform thanks, but really, i've had lots of help.

koolman

1:22 PM

Can any one have some easier way as said by sammy for this

physics.qandaexchange.com/?qa=596/rotation-of-a-wheel

Kenshin

yes

koolman

What

Kenshin

i just want to check my simple solution gives the right answer then i'll tell u

koolman

Ohk

John Rennie

Ooh, I've got Where in the world now. I wonder if it has to do with updating your profile info ...

Kenshin

1:31 PM

@koolman ok I know it

@JohnRennie no I think it is doing any action today

I think it is to do with today's date, and your location in the world

congrats on the new hat :)

@koolman r u ready?

John Rennie

Ahhh. I wonder if you got the Moon because it's night time in Aus while AFT and I got the Sun because it's day time here ...

Kenshin

yeah that makes sense

what is AFT

Slereah

ass field theory

Kenshin

oh

koolman

@Kenshin sammy has edited his answer with more easier way is it same you mean

AccidentalFourierTransform

1:34 PM

what @Slereah said.

John Rennie

@Kenshin Accidental Fourier Transform

Kenshin

@koolman my way is just (1) calculate the angular acceleration = 3

koolman

How

Kenshin

oh because angular acceleration*r = tangential acceleration

this is a known formula

koolman

Yea

Kenshin

1:36 PM

and we're given tangential acceleration = 3

and r= 1

so therefore angular acceleration = 3

John Rennie

ass field theory - I thought asses were already quantised. Why do we need a second quantisation approach? And precisely what are asses excitations of? If I get very excited might I end up with two or more asses?

Kenshin

then step (2) calculate tangnetial acceleration at point P

koolman

Ohk @Kenshin

Kenshin

at point P, r = 1/3, angar accleration is the same = 3, so 1/3*3 = 1

so tangential acccleration at P is 1

relative to the disk

but the disk is also moving at 3

so total tangential relative to ground is 1 + 3 = 4

this is the tangential component

the other component is the centrepital component

koolman

Yes

Kenshin

1:38 PM

which is angularvelicty^2*r

AccidentalFourierTransform

kiss my ass to all orders in perturbation theory

Kenshin

= 9^2 * (1/3) = 3

then you just get the resultant force as root of 3^2 + 4^2

@koolman so there is no need to differentiate the position of P as sammy has done if you already know your formulas

koolman

I think it is angularvelicty^2/r

Kenshin

na that's not correct

koolman

@Kenshin hyperphysics.phy-astr.gsu.edu/hbase/cf.html

Kenshin

1:42 PM

@koolman v there is tangential velocity

if you want angular velocity it becomes angularvelocity^2*r

koolman

@Kenshin oh sorry

Kenshin

since angular velocity*r = tangential velocity

koolman

Got it

This one is better , thanks @Kenshin

Kenshin

np

koolman

@Kenshin could you also explain me the edited answer of sammy

How he has get the linear acceleration at point P

Kenshin

1:48 PM

i dunno sorry

koolman

Np

@Kenshin you have the secret hat

Cool

Kenshin

ty

Secret

creepypasta.com/string-theory

Swapnil Das

Hi again!

Secret

2:14 PM

newscientist.com/article/…

The shortcomings for some type of all powerful entity is their domain specific rein. If you can fool them into a realm where they are powerless, they will be controlled very easily

To lure the all powerful into a simulation within a simulation...

Secret

2:49 PM

1

Q: What kind of waves can be/are produced by accelerating strong /weak forces

Accelerating masses are now confirmed to produce gravitational waves. Also it is known that accelerating charges (electrical) produce EM waves. But what kind of waves are produced when particles interacting via strong or weak force accelerate. Are waves even produced at all.

waves weak-interaction strong-force

Bu they are different, and they are insanely short ranged

Suhrid Mulay

3:09 PM

Yipee got a secret hat just now

ACuriousMind

"Where in the world" seems easy to get

user228700

@JohnRennie: Are u around?

John Rennie

I'm here ...

Did you just get my mail?

user228700

Yes.

user228700

U sent it urself..?

John Rennie

3:15 PM

After I mailed you I thought why not just sent the receipt directly to that chap at TNT, so that's what I've done.

user228700

Ah, I see, okay. I'm sorry I read the mail a bit late...just now, actually.

John Rennie

If you've sent a copy as well that's all to the good.

user116211

0

Q: Quantum Field Theory in position space instead of momentum space?

What are the reasons why we usually treat Quantum Field Theory in momentum space instead of position space? Are the computations (e.g. of Feynman diagrams) generally easier and are there other advantages of this formulation?

quantum-field-theory

user116211

1

Q: Position space Feynman rules to momentum space

For example consider $2\to2$ scattering in scalar $\phi^4$ theory. When the in/out coming positions are fixed, it is easy to calculate in terms of contractions. When we fix the incoming / outgoing momenta instead, how can we use the Feynman rules in that case? In principle one can expand all th...

quantum-field-theory scattering fourier-transform feynman-diagram s-matrix-theory

user228700

No, I read both e-mails just now.

John Rennie

3:17 PM

@Kaumudi.H We aren't dealing with the most efficient company ever to grace Hindustan :-)

user116211

Are the two posts above in anyway related?

user228700

:-) No, we're not.

John Rennie

Anyway, hopefully the message will get through.

@Kaumudi.H at least all this hoo haa adds a certain interest to developments. When you finally get the laptop it will feel as though you've triumphed ina great quest! :-)

Incidentally it wouldn't hurt to ring tomorrow and check the e-mails have been received.

AccidentalFourierTransform

with my new hat, my avatar looks like nyan cat :D

ACuriousMind

@AccidentalFourierTransform lol

AccidentalFourierTransform

3:25 PM

@ACuriousMind your hat is too mainstream, sorry

ACuriousMind

I haven't got any of the fancy ones yet :/

user228700

@JohnRennie Indeed, it certainly will :-)

user228700

@JohnRennie Oh, alright, I'll do it.

Lalylulelo

Hi :) Quick question: is it possible to see questions on SE from multiple tags at the same time?

AccidentalFourierTransform

4

ACuriousMind

3:35 PM

@Lalylulelo Yes, just type [tag-1] [tag-2] [tag-3] into the search box to find all questions tagged with tag-1, tag-2 and tag-3

Lalylulelo

thanks!

ACuriousMind

Sigh...if the algorithm for the snaphat is pedantic and doesn't count 30 minutes and 2 seconds as 30 minutes, I can't get the hat for this answer :/

2 seconds!

Lalylulelo

it seems to give the questions that are tagged with tag-1 and tag-2 and tag-3. But is it possible to have questions tagged with tag-1 or tag-2 or tag-3?

ACuriousMind

@Lalylulelo Type OR in between the tags ;)

Lalylulelo

ok, I tried by myself :p thanks !

ACuriousMind

3:41 PM

Thanks whoever voted that up, it appears the algorithm is pedantic

I need to type faster or give answers with less formulae :P