The h Bar

vzn

00:26

@Obliv good academic/ scientific work is "selfless" in general. likely "our kids" will face many of the issues the superintelligence book raises. there are "only" ~2 decades between generations.

@SirCumference try Code Review

Sir Cumference

@vzn Oh crap

Wrong person, wrong chat

Sorry

user507974

00:47

guys

is there a name for this equation

${C(x,t)-C_s}\over{C_s-C_0}$ C_s might be some other subscript in many contexts

DanielSank

01:40

@BernardMeurer <3

Bernard Meurer

@DanielSank <3

That was positively unexpected hahaha

I literally just sat in my chair

DanielSank

@ChrisWhite I have figured out SQL in the past...

What's "gini"?

@BernardMeurer Then our meeting was fated.

Bernard Meurer

Gini is a coefficient to measure distribution

DanielSank

Forget that blonde.

Bernard Meurer

it's used to measure how unequal wealth is distributed in countries usually

At least that's the gini I know

Never! She only cooks texan <3

DanielSank

01:43

@BernardMeurer I'm not even sure what that means.

What is Texan food?

Wait a second, she's American?

Bernard Meurer

Yeah she is dood, hadn't I mentioned that?

Lel

DanielSank

@Jiminion Is that a Groucho Marx line?

@BernardMeurer yes but I was confused because the information was conveyed through some bizarre description of her sister's friend or some such thing.

Bernard Meurer

@DanielSank I have trouble being clear a lot of times

FreezingFire

05:04

I hope this is the right place to request an answer to the question here: physics.stackexchange.com/questions/250330/…. A short description: in electrostatics, if some conductor is earthed, what happens to it? If this isn't the right place, where am i supposed to request answers of willing users? Thank you very much!

John Rennie

@FreezingFire the "Earth" behaves like a giant capacitor i.e. you can push charge onto it or pull charge off it without changing its voltage (very much).

FreezingFire

Umm, yes, but actually i am not able to apply that concept to a specific problem (i.e. use it mathematically), that is mentioned in the question (too long to put here). Could you help me with it?

user54412

@Slereah There are the occasional papers I never read too closely. Once we discovered that galaxies really are distributed homogeneously beyond a certain scale, interest in this waned a lot, since it probably would only ever be a small correction to things.

FreezingFire

@JohnRennie Umm, yes, but actually i am not able to apply that concept to a specific problem (i.e. use it mathematically), that is mentioned in the question (too long to put here). Could you help me with it?

John Rennie

05:24

@FreezingFire OK let's take your case (a). Plate B starts off with a charge +Q, so it's attracting electrons onto plates A and C.

However electrons can't flow onto plates A and C because there is nowhere for those electrons to come from. OK so far?

FreezingFire

@JohnRennie Yes.

@JohnRennie Actually, when the plates are not earthed, i am able to tell the charge, distribution as i have said in my last comment on Farcher's answer! But anyways, i would like to hear you out completely...

John Rennie

When you close the switch S1 you are connecting the plate to an effectively infintiely big ball (the Earth) of mobile charges. So charge flows off the Earth and onto plate A. Because the capacitance of the earth is so big there is no assciated change in potential.

So a charge -Q flows off the Earth and onto plate A.
Plate C is unaffected because it still has no way for charge to flow onto or off it.

skill patrol

Congratulations @ChrisWhite and @JohnRennie on your room owner appointments.

user54412

^ the temptation to delete that message just to be ironic...

skill patrol

:-D

it's nice to see non-mods get the job

FreezingFire

05:36

@JohnRennie Okay, so what i understand from this is that the Earth remains practically unaffected, but then why the specific value of -Q appears on the plate? Why not some other arbitrary value of charge? Again pondering a bit more, it seems to me that the two plates want to behave like a capacitor, so that they have equal charges on opposite plates. Am i correct in thinking so?

John Rennie

Yes, the plates are behaving just like a capacitor. Indeed they are a capacitor.

I'm trying to think of a simple way to explain why the charge that flows onto plate A is equal and opposite to the charge on plate B. Give me a moment to think about it ...

Actually I'm going to have to drop out for a bit. I'm currently working and something has come up.

Is it just the issue of why the charge on plate A is equal and opposite to the charge on plate B?

FreezingFire

05:52

@JohnRennie Yes. I understand that the positive charge will attract a negative charge from the earth onto the plate A (because of attractive force), but i don't understand why only a value of -Q is attracted! It could probably attract a lot more (or less)! Also, i am not able to connect this to the concept that earthing "only" sets the potential of a point to zero. Thank you for your interest in this! :D

lucas

06:28

Hello dear John Rennie.

Are you there?

John Rennie

I'm around, but I'm at work now so I may need to drop offline from time to time

lucas

Thank you.

I answered a question, but they downvote me.

Do they want me to leave this website?

Why they don't like me?

Can you help me to know?

John Rennie

This answer:

-1

A: plz solve my question

We use the polar coordinate. $\sum F_\theta=mgcos\theta=ma_\theta$ $a_\theta=gcos\theta$ While body is on the sphere, r is constant. So, we have: $a_\theta=R\alpha$ $\alpha=\frac{gcos\theta}{R}$ $\alpha d\theta=\omega d\omega$ $\frac{gcos\theta}{R} d\theta=\omega d\omega$ $\frac{g}{R} (s...

lucas

yes

John Rennie

The question posted by Bratin Kundu is just an attempt to get us to do his homework.

That is, he wants us to help him cheat.

lucas

06:34

Did he downvote me?

John Rennie

And we don't do that in this site. I don't know who donvoted you, but I expect it was because you are helping someone cheat.

knzhou

@FreezingFire Earthing sets the potential of plate A equal to the Earth. That means the integral of the electric field, along a path starting at the Earth and ending at, say, the left end of plate A, is zero. If the plates are big, having plate A and plate B have opposite charge will guarantee this happens, because then the field outside the two plates will be nearly zero.

lucas

How can I know that it was cheat?

John Rennie

Because it's obviously just a homework question.

lucas

When I answered that question it wasn't blocked.

John Rennie

06:36

Bratin Kundu isn't asking about any fundamental concepts in physics. He has just copied the question from his homework into this site.

lucas

If they continue like this, I loose features.

Comment, for example.

I want to help the others. I like learn and teach.

John Rennie

I understand that you want to be helpful, and that's why most of us are here on this site. But you help people most by enlarging their understanding of physics. Just doing their homework for them doesn't achieve this.

lucas

Thank you very much because of your time. May I ask a little question else?

Do you have time?

John Rennie

Yes, please ask.

lucas

Do you think I am stupid? May you tell your idea comfortably?

Sorry for my poor English.

skill patrol

06:45

if you judge a fish by its ability to climb trees, it will go through its life believing it is stupid

lucas

I guess they think that I know nothing about physics. Do you think same?

Please simple sentences.

skill patrol

do you understand what my last post means?

lucas

I am using dictionaries

What do you think about my abilities?

skill patrol

even native speakers use dictionaries :-)

John Rennie

I doubt anyone thinks you are stupid. Your answer to the question is a perfectly good answer. My guess is that it was downvoted because you should't be encouraging homework questions, not because it was a bad answer.

lucas

06:50

Thank you. Forgive me because of bothering you. I hope chat you in the future if you want. Thank you again. Good luck.

John Duffield

@Jiminion : of course fields really exist. According to Einstein, a field is a state of space.

skill patrol

07:12

Do you @JohnDuffield have a thesaurus?

Slereah

hello

so anyway

Non-perturbatively, $\varphi^4$ is trivial

Do we know about the triviality or non-triviality of other interacting theories

(of the SM)

Like do we know if EM is trivial or not

Bass

@Jiminion Please note that almost all experts on this site do not agree with many statements by JohnDuffield.

Slereah

Why the "almost"

John Duffield

07:28

@skillpatrol : sure.

John Rennie

@Jiminion Hmm, that's not my intention. If you think I'm getting a bit negative that's something I should look at ...

Slereah

Hm

In LFT, I guess that the energy is gonna be something like...

$$\langle \hat T_{\mu\nu} \rangle_\omega = \lim_{\Delta t \rightarrow 0}\int_{\varphi(t,\vec{x}) = \varphi_\omega(t,\vec{x})}^{\varphi(t,\vec{x}) = \varphi_\omega(t+\Delta t,\vec{x})} (\prod d\varphi(x)) T_{\mu\nu} e^{iS}$$

Does that sound about right

Slereah

07:57

Does that sound like a slice of fried gold

yuggib

@Slereah no one knows whether $(\varphi^4)_4$ is trivial or not

user116211

Slereah

I have read it a few times

Is it only a hunch?

user116211

Book - An Introduction To Algebraic Topology by Joseph J. Rotman

yuggib

$(\varphi^4)_{\leq 3}$ is not trivial, $(\varphi^4)_{\geq 5}$ is trivial

Slereah

08:03

I see

user116211

@Slereah you saw it earlier?

yuggib

(at least by means of lattice regularization and then limiting procedure)

Slereah

Same thing as classification of manifolds :p

Damn dimension 4

Why do we have to live in 4D

yuggib

:-D

the reference for triviality are this

this

and probably this book

as far as I know

Slereah

There doesn't seem to be a lot of stuff on LFT and non-linear operators

yuggib

08:09

@Slereah what do you mean by LFT and non-linear operators?

classically?

Slereah

I mean operators of the type $\langle \hat \varphi(x) \hat \varphi(x) \rangle$

yuggib

that is not an operator...

Slereah

The product of more than one operator at the same spacetime point

$\hat \varphi(x) \hat \varphi(x)$

IF YOU PREFER

Mister picky

yuggib

still not an operator

Slereah

Maybe but still it is commonly used

yuggib

08:11

and if it was, it would be linear

Slereah

How else do you compute the energy of something

yuggib

it is a linear operator acting on the space of quantum states

Slereah

You know what I mean :p

Then again, i suppose that I can use the usual method

$$\lim_{x \rightarrow y} \langle \varphi(x) \varphi(y) \rangle$$

yuggib

good luck in giving sense to that

usually distributions behave pretty badly in one point

or when multiplied

Slereah

Yeah that tends to be bad

But there are regularization procedures for it

yuggib

08:14

take a look at him

he works on that

Slereah

neat

I wonder what those procedures translate as in path integrals

IIRC the simplest is just really to substract the vacuum expectation of Minkowski

it's a pretty simple quick and dirty scheme

yuggib

I don't know

or better, I don't remember

when I did that physically, we used either dimensional or mode regularization

Slereah

What is mode regularization

yuggib

you expand the path in a Fourier series and cut high modes

Slereah

Oh

So it's just the energy cutoff thing

yuggib

08:17

it is not covariant

Slereah

yeah I recall

yuggib

but still works

Slereah

Substracting the Minkowski vacuum only works in flat space, unfortunately

It's equivalent to normal ordering

yuggib

we used mode reg here

Slereah

We?

yuggib

08:19

@Slereah yeah but it is always not sufficient

Slereah

Which one are you!

yuggib

:-D

regulars here know

;-P

Slereah

I hope you're not Falconi

Of the Gotham Falconis

yuggib

I'm a mobster yes

Slereah

Then again I'm not sure I can trust someone from the university of ballony

yuggib

08:21

we taught you all what a university is

Slereah

08:35

blah

I should go back to doing Peskin

Chapter 3 exercizes are so not fun

Can you calculate the stress energy tensor in a scattering btw

I'm not sure I've ever seen it done

I guess the in and out are pretty easy since it's basically free but can you do it around the collision

Like can we know the energy densities in a collision event

Perturbatively or otherwise

I mean I guess the natural way would be to get the SET from the propagator as a perturbative series, but since I've never seen that done, I am suspiscious of whether that's a good idea

yuggib

09:21

I don't know

Slereah

Hm

maybe I should give it a try once I'm done with Peskin

Danu

11:13

Is the "HEP Post Doc Project" website down already?

...wonder what happened

Slereah

Slander lawsuits?

skill patrol

too many "rumors"

Slereah

I hear this professor steals PHD students bones to grind them into flour for his ogre bread

skill patrol

don't believe everything you hear :P

yuggib

12:07

@Danu it was doomed

I mean, it is good to have some sort of feedback on PhD/Postdoc advisors

but with anonymous comments on the internet you can only obtain legal issues

The Dark Side

16 hours ago, by user507974

Feel tempted to add a feature request:

Ping ACM every time anyone posts that.

But the only problem would perhaps be, with too much pinging, ACM would be attending to all sorts of stuff which is homework like/ otherwise off topic for the site.

Which means a major timesuck, which'll work like a negative feedback loop.

And then, ACM will stop responding to pings, like the recent "Why are you pinging me for that" explosion?

But nevertheless, this supernatural gimmick pinging system is an irresistible itch.

David Z

12:23

@TheDarkSide y'know it could be done... :-P

The Dark Side

:P

skill patrol

well, without 0celo7 around he's got a lot of free time :P

yuggib

@skillpatrol the poor guy

skill patrol

such are the dangers of pushing the envelope one too many times

yuggib

12:38

?

Danu

@yuggib I assume you're not aware of the HEP Rumor Mill? :P

yuggib

@Danu I'm proudly HEP free since the end of 2008 ;-P

however a quick google search suggests there are no (possibly defamatory) comments there...

Danu

12:59

@yuggib Fair enough :)

Secret

13:25

This integral pops up in my research project (convolution of a gaussian and a maxwell boltzmann)

Not only it is nonelementary, it does not even have a closed form in terms of known spaecial functions (and Mathematica is known to have a lot of crazy special functions defined)

currently trying to figure out the best algorithm to numerically curve fit with it

yuggib

are you sure it has no closed form?

completing the square and using the gaussian integrals for powers of $t$?

it will involve some change of variables etc, but nothing impossible

(at least if you are integrating on the whole positive line)

Secret

Well, I never took noticed that I can complete the square. Currently calculating it now...

I am so bad at integral intuition

yuggib

13:40

theoretical physicists have a professional deformation towards completing the square :-D

Slereah

PROTIP

Don't trust Wolfram Alpha to do complicated integrals

Get yourself

The Book

$user image$

yuggib

good ol' gradstein

Slereah

useful for integrals and hammering in nails

yuggib

a functional tool!

Secret

@Slereah Bonus point that matlab have trouble on that integral too. As for manually, after being enlighted by yuggib of a simple thing that I overlook, it seems the result is promising... I am expecting it might be some kind of gamma function because of a gaussian and a sqrt term

ACuriousMind

14:10

@yuggib It's a consequence of our fetish for the harmonic oscillator, I think ;)

yuggib

@ACuriousMind does there exist something else?

Slereah

Everything is a SHO

GR is nothing but a spacetime of harmonic oscillators

Little springs make up spacetime

ACuriousMind

@yuggib Probably not

Maybe Atwood machines :P

Slereah

5

Q: What is the terminal velocity of a sheep?

Inspired by this question on Gaming.SE Using actual in-real-life physics, what would the terminal velocity of a sheep actually be? I would assume it would be around 50m/s, but I might be wrong. Bonus question: What would the terminal velocity of a chicken be? Animal-friendly answers preferred.

Do real physics and experiment, I say

Secret

14:26

ok it reduces to something nice
$$Gaussian * Maxwell Boltzmann=\int_{-\infty}^{\infty}\sqrt{A-bx}e^{-x^2}dx$$
which can be easily evaluated into something involving a gamma function

ramsay

How to find this:$$\int^{+r}_{-r} \sqrt{\dfrac{r^2}{r^2-x^2}}$$
i know to find integral if this were to be an indefinite integral but his is a definite with limits how to proceed?

ACuriousMind

@ramsay If you know the indefinite integral, what stops you from just applying the fundamental theorem of calculus?

yuggib

@Secret I hope there are some absolute values in that square root... ;-)

ramsay

but i am getting confused, i replaced $x$ by $\sin \theta$ but i don't know what limits will become if i change $dx$ to $r\cos \theta d\theta$

yuggib

hey hey

you can't use $r$ as a variable of integration

ramsay

14:34

hein! i didn't get you (sorry)

yuggib

which change of variables do you want to make?

ramsay

i wanna change $x $

yuggib

i.e. $x=\sin\theta$?

ramsay

oh, hoho! i made typo $x=rsin\theta$

yuggib

ok

ramsay

14:37

so $dx=rcos\theta d\theta$

yuggib

then when $x=r$, $\theta=\arcsin 1$

ramsay

oh, i got it thanks @yuggib :-D

Secret

$=CONSTANT\left(\left[\sqrt{A-bx}\right]^{\infty}_{-\infty}\right)$

...??? that... does not look good...

yuggib

@ramsay no prob

@Secret why? I really don't think so...

the integral (apart from the problem of negative square root) is indeed convergent and finite

and the negativity of the square root will only give you an imaginary part

ramsay

a silly question about GR: einstein said it was the earth which was accelerating up not the apple(which is accelerating down in earth's frame), then what happened on the other side of the earth?

Secret

14:44

@yuggib How to evaluate $$\lim_{x\rightarrow -\infty}\sqrt{A-bx}$$ because just looking at its graph it does not seemed to converge at all?

Slereah

>limit

It diverges to $-\infty$

Limit of a function

In mathematics, the limit of a function is a fundamental concept in calculus and analysis concerning the behavior of that function near a particular input. Formal definitions, first devised in the early 19th century, are given below. Informally, a function f assigns an output f(x) to every input x. We say the function has a limit L at an input p: this means f(x) gets closer and closer to L as x moves closer and closer to p. More specifically, when f is applied to any input sufficiently close to p, the output value is forced arbitrarily close to L. On the other hand, if some inputs very close to...

chain rule

and algebraic limit theorem

ramsay

@Slereah are you forgetting $i=\sqrt{-1}$, aren't you?

Slereah

$i\infty$ then

ramsay

sounds cool :-D

Slereah

Depending on where you put the branch cut for the function

i guess

Secret

14:51

Weird, let me check my workings again, a maxwell bolzmann and gaussian should not convolve to get a divergent thing

yuggib

@Secret yeah, but the integral there converges

John Rennie

@ramsay you are implicitly thinking of acceleration as the second derivative of some position variable $a=\frac{d^2x}{dt^2}$. However the acceleration referred to in this case is proper acceleration defined as $a^{\mu}= \frac{du^{\mu}}{d\tau}+\Gamma^{\mu}_{\alpha \beta}u^{\alpha}u^{\beta}$.

yuggib

this is sure

no doubt

it is not what you wrote

it will be something involving gamma functions

and the constants $A$ and $b$

but finite

ramsay

@JohnRennie makes sense(but not 100% since i don't know vigourous GR)

vigorous*

John Rennie

rigorous ?

Slereah

14:59

vigorous GR is when you lift GR books every day

Stephani is a good workout

John Rennie

@Slereah most GR books are too heavy to lift!

ramsay

hehe

Slereah

Nah

Hawking Ellis is pretty light

Physics Meta

15:10

-1

Q: Conservation of momentum (angular and translational)

A ring of radius R and mass M lies on its side on a frictionless table. A bug of mass m rests on the ring. The bug starts walking on the ring with constant speed v relative to the ring. Please Describe the motion of ring relative to ground frame. (In some questions the ring is being pivoted, but...

discussion

lucas

15:29

Hello dear John. Do you have time?

FreezingFire

@knzhou Whoa! That clears it up pretty well! Thank you so much for your help! :D

John Rennie

@lucas Hi Lucas. Yes I'm free at the moment.

lucas

Thank you.

Do I bother you?

If you busy, I can come later.

barrycarter

Dear John letter?

John Rennie

@lucas No, I wouldn't be in the chat if I wasn't happy for people to ask me questions :-)

@barrycarter hello stranger!

barrycarter

15:37

@JohnRennie LOL :) Hi there!

John Rennie

been off doing proper work? :-)

lucas

@JohnRennie May I ask why my question is blocked?

barrycarter

I was gonna say! I got more done in the last 2 days than in the weeks since I started chatting.

John Rennie

@barrycarter it is a massive time waster. But then I only hang around in the chat when I have the time to waste :-)

barrycarter

@JohnRennie I'm retired, but pesky things occasionally require me to view that large scary ball of fire in the sky.

John Rennie

15:39

@barrycarter retired as in completely retired?

I ask because I retired a few years ago but rapidly got bored and started working part time again.

barrycarter

@JohnRennie I once claimed I was constantly bored and had an infinite amount of time to kill. This is apparently not true. Yes, completely retired. I tutor students and do programming for fun, but only SS pays me.

John Rennie

I work for my old company 6 a.m. to 8 a.m. doing the early morning checks to ensure nothing has died.

barrycarter

@JohnRennie ARGH! I have seriously been considering that. I can't wrap my mind around working when I don't have to.

Jiminion

@JohnRennie I don't. I think it's a reflection of your efforts to explain very complicated subjects.

John Rennie

@barrycarter It suits me as I wake up early anyway, and from 8 a.m. the day is mine :-)

barrycarter

15:41

@JohnRennie I was going to say-- getting up at 6am wouldn't be good even if I DID need the money.

Jiminion

@DanielSank Yes, a variation of a Groucho Marx line. (I think the original had to do with reading a good book.)

John Rennie

@barrycarter when I was a student you'd fight to get me out of bed before lunchtme, but as I've aged I think my body clock has shifted to a shorter day length.

barrycarter

@JohnRennie hmmm... I've returned to staying up nights (sometimes) in my old age. Ironically, I'm probably p at 6am British time.

@JohnRennie Some people believe 24 hours isn't natural. The earth used to rotate faster :)

Secret

barrycarter

@Secret Cool red arrow.

Secret

15:44

I tried to integrate this by integration by parts, and then I got the aforementioned divergent sqrt term

I don't know how to integrate this in terms of gamma functions because gamma function is not defined for negative integers

barrycarter

@JohnRennie You're only an evil moderator here, not on the Physics site, right?

John Rennie

@lucas I voted to close your question because I couldn't understand what you were asking. The question didn't make sense.

Secret

The integral in question
$$\int_{-\infty}^{\infty}\sqrt{K-\sqrt{B}t_3}e^{-t_3^2}dt_3$$

where K and B are independent of $t_3$

John Rennie

@barrycarter correct, but I'm not a chat moderator just a room owner. For example I can't suspend you. All I can do is move messages to trash ("trash" is a room set aside for junk posts) or "kick mute" you.

barrycarter

@JohnRennie Kinky... but you can't edit questions on the actual site right?

John Rennie

15:46

I'm not sure what "kick mute" means, but I think it's a 5 minute suspension - sort of a time out to cool off.

barrycarter

@JohnRennie You do realize that it probably just pisses people off more, right?

@Secret I could run Mathematica on it, but that would be of zero help to you.

@Secret I suspect that, with proper values of K and B, this might be a probability distribution.

John Rennie

@barrycarter I have to agree with you. If I were suspended for 24 hours I'd probably have cooled off after sleeping on it. But if I were suspended for 5 minutes I'd come back incandescent with rage. I can't see myself ever using the kick mute.

barrycarter

@JohnRennie The 30m isn't bad either. But 5m is really just making it worse.

John Rennie

Possibly the kick mute is meant as a last resort measure while we scream for the real mods.

e.g. if someone has lost it and is screaming obscenities.

barrycarter

@JohnRennie Ah, while you wait for backup, makes sense. Plus I suppose you could do it multiple times, although, again, that would just piss people off more... which actually sounds kind of fun.

@JohnDuffield I would like to publicly thank you for sending me a signed copy of your book.

17

Q: My question was closed on Phys.SE. Can you recommend me another internet site where my question might be on-topic?

My question was closed1 on Phys.SE. Can you recommend me another internet site where my question might be on-topic? Here we keep a list of other internet sites that might help students2 of physics. One site per answer. To keep the list at a reasonable size, please only include sites which fulfil...

discussion closed-questions homework faq-proposed

John Rennie

15:52

@barrycarter aha, see:

56

A: Impose a re-entry delay on users kicked out of a chat room

This has been implemented now. The short story is: room owners can kick abusive users, who will then be banned from re-entering the room for a certain time. Of course you want not just the short story but all the dirty details, so here they are: In the user popup that appears when you click on ...

barrycarter

@JohnRennie Do you have sufficient magic powers to edit the question above or at least combine all the answers into a single answer?

John Rennie

The first kick-mute lasts one minute, the second five minutes and the third half an hour

barrycarter

@JohnRennie With great power comes great responsibility. But with a crappy little power like this, you get nachos.

John Rennie

@barrycarter :-) I am a petty god.

barrycarter

@JohnRennie Aren't they all :O

John Rennie

15:55

@barrycarter on the main site I have no special powers. You get a few privileges with a high rep but nothing dramatic. I could write a new answer combining all pervious answers, but I couldn't delete the previous answers.

barrycarter

@JohnRennie You are worthless to me :P

John Rennie

In any case I suspect people like having the separate answers voted on separately. It puts the most useful links at the top.

barrycarter

@JohnRennie Trueish, but I think this is more of a list question, even more so "stop bugging us and go look at these sites", in the hope they'll find their answer and won't come back. I'm trying to give a better "canonical" answer to homework questions.

@JohnRennie Who has the power to edit templates?

John Rennie

@lucas I just didn't understand the point you were trying to make. If you pick any point in the rolling object it moves in an epicycle like motion so it doesn't have a centre of rotation, let alone two of them. I can't see why you think there is a paradox there.

@barrycarter I am worthless to you again I'm afraid :-)

barrycarter

@JohnRennie I already knew you had feet of clay. You're up to the knees now.

John Rennie

15:59

I'm really a golem and clay all the way through

Gustavo6046

Hi guys

barrycarter

An interesting question: are there any points on the wheel that trace out a path that doesn't cross itself.

John Rennie

Hi

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