The Factory Floor

overactor

7:06 AM

Someone serially upvoted a bunch of my answers :(

@DaaaahWhoosh I know I'm late, but you should really take wolfram alpha.

bilbo_pingouin

@overactor serial upvoting is better than the other way around, isn't it?

@overactor and for that, I'd simply take a smartphone and make sure I've got 4G connection on the quest site :)

overactor

@bilbo_pingouin But SE will take the rep away, no?

bilbo_pingouin

I don't know if it automatic... so it really depends on how much of a serial effect it is

overactor

7:24 AM

8 answers in a row

bilbo_pingouin

yes I was looking at it. A fair few of them are accepted answers... and while some are on recent questions, some aren't.

So it is likely that you indeed were targeted for a serial upvote. Well in the worst case, just assume you never got that extra rep

overactor

@bilbo_pingouin That's what I'm doing :)

bilbo_pingouin

if you want to clarify, you could probably ask a mod... who might be able to check who's been behind it

overactor

@bilbo_pingouin Also important to note that I have only written 15 answers to date

@TimB can mods do that?

bilbo_pingouin

it might still be a bit early for Tim... he's one hour behind us :)

overactor

7:34 AM

and yet so far ahead with rep...

bilbo_pingouin

that indeed :)

but rep does not prevent sleep

Tim B

8:33 AM

We do have tools to analyse voting etc. The automatic systems catch most though. Obviously I can't discuss just what tools we do or don't have. 8 upvotes may be a coincidence

bilbo_pingouin

it could be. But 8 out of 15 in a short time, and as far as I have seen those were the 8 already most voted... but if it isn't, good for overactor :)

overactor

9:15 AM

20

Q: Would a fighter pilot with an invincible space ship be able to conquer the galaxy?

Setting Not so long ago, in a galaxy not too far away, there were two civilizations at war. Both were at war because the leaders of both wanted more and more power. Both were advanced and mined the stars. Both had an extensive fleet of powerful ships — everything from fighters to transport ships...

@TimB protection seems necessary

@TimB you're speaking from your experience, you have over 300 high quality answers sitting around gathering sporadic upvotes, I have 15 answers. I've never gotten anything close to 8 upvotes on 8 different answers before. But I'll assume the system will catch it if it was not coincidence.

Meanwhile my personal favourite out of my answers remains my lowest voted one :(

bilbo_pingouin

@overactor in principle I should be able to do it (3500 rep), but I don't know how... ^^"

anyway that question is off-topic and should be closed, IMO

overactor

9:31 AM

@bilbo_pingouin It's an edge case imo

bilbo_pingouin

"Any question at least a day old can be protected and unprotected by users that have the privilege." it was asked 14 hours ago

so that may be the reason I can't find any link for it

yep. I can see on on older questions

@overactor I don't think so. It is about the action of the single character. Who had a particular training. Given a special vessel. I don't see how that affects the building of the world.

@overactor tell me about it. One of my favourite answer still has 0 votes.

overactor

@bilbo_pingouin oh

can mods do it more quickly?

bilbo_pingouin

I've never been mod, so I don't know. In any case, you did ping Tim about it, so he might be able to see it.

overactor

What answer with 0 votes are you talking about?

bilbo_pingouin

war tactics with dragons and humans

it was on an old question, so that was probably the reason. And there were already some answers... but nevertheless I like that answer.

overactor

9:43 AM

I'll go and read the question

bilbo_pingouin

well if you've got time to spare, go ahead :)

Tim B

michael is already active on that question so I'll not interfere and mess up what he might be doing

and yes mods can protect immediately

there's also automatic systems that will protect if certain criteria trigger

overactor

@TimB I didn't know that

Hey Tim, what's your favourite underappreciated answer? (out of your own answers)

Tim B

9:56 AM

I don't have a specific one, could list a few

0

A: Implications of 'Respawning'

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0

A: Cloning through mating

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0

A: Would scientists call magic "magic"?

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0

A: Weaponising a city

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0

A: Sky Travel in Dark Fantasy World

The classic case here would be the Pegasus, it's a winged horse so already familiar to people as a mount. You can see them as being a very expensive upgrade on the horse, needed much better food and care, and costing an absolute fortune. They would be ridden or used to pull enchanted vehicles. ...

bilbo_pingouin

(not wanting to interrupt, but Michael did protect the question)

thanks @overactor for the upvote :)

overactor

@bilbo_pingouin You didn't get it because you asked, you got it because it was a good answer.

bilbo_pingouin

yes, but you read it because I mentioned it... otherwise it would have gone on unnoticed ;-) so at least thanks for reading it

overactor

@TimB what just happened is okay, right?

Tim B

10:22 AM

if its a good answer upvote it, no matter how you found the answer

so long as the vote is about the answer not the person it's fine

but being aware of the line and staying clear of it is a good idea

overactor

@TimB Yeah, I'm keeping myself from going through a bunch of answers by a user and upvoting the ones I like

Tim B

yeah, that's starting to push the line

doing a few is fine, especially if you do ones by other people too

overactor

10:54 AM

When is HDE usually around here?

Tim B

11:23 AM

he's US timezone

so I wouldn't expect to see him for a few hours at lesat

overactor

@TimB ok, do we have any other rather profilic users who are rather good at physics and/or math?

Profilic as in, they are sometimes in chat

bilbo_pingouin

I might do some things... depending on needed time ;)

overactor

@bilbo_pingouin I was thinking some more about the galactic bridge question

bilbo_pingouin

what about it?

overactor

And wanted to see if the bridge could actually hold up under its own gravity

bilbo_pingouin

11:37 AM

I'm pretty sure the bridge cumulate a few issues... and gravity is one of them

overactor

So I started by assuming that the bridge was a infinitely long sequence of 10,000kg spheres with 1m between the centre of each following sphere

and tried calculate the total gravitational force on the first sphere:

Tim B

the force will be finite, that's the good news

overactor

result

It's not even that large

approx 1.6 time the force between the first two balls

Tim B

yep, sounds about right

overactor

So then I figured I should reduce the distance between the balls and make them lighter and take the limit of that

first I singled out the infinite sum

Hmm in another tab that gives me pi squared over 6 a squared

pi^2/(6a^2)

So then I checked what the limit did

Okay, this wolfram alpha linking isn't working out very well

huh, now it works?

anyway, the force stays constant, shich is a problem, because the mass is approaching 0

Now I'm pretty sure I made a mistake

I think the problem is that I'm treating the segments as spheres, this works reasonably well at large distances and at largeish sizes

but the different of two very thin rectangles very close to eachother and two pointmasses of teh same weight very close to eachother is what's causing teh error I think

basically, I'm making the road infinitely thin, but still retain the same weight

which results in infinite density

Tim B

11:55 AM

try modelling it as a cylinder?

overactor

@TimB I don't know how to take a limit of that

Tim B

me neither, google probably does though

overactor

I don't know how to calculate the gravitational pull between two cylinders on the same axis

hmm

I guess I could try googling that

bilbo_pingouin

Wait, you want to calculate the total gravitational force on the first sphere? Wouldn't the planet gravitational field overshadow that?

wasn't that the question that wanted to build a bridge from a planet to a star ?

overactor

@bilbo_pingouin I was first trying to see if the bridge would collapse under its own gravity if it gets exceedingly long

@TimB Can't find it, but I did find a way to calculate it

would be easier with squares maybe

still difficult though

I should take the two squares and start subdividing them and consider each segment a point mass

bilbo_pingouin

12:16 PM

first off, if you consider a bridge without any other influence, the gravitational force will probably be worst at the centre, wouldn't it?

overactor

and then take the limit of that

@bilbo_pingouin it would cancel out at the centre, no?

bilbo_pingouin

hm... I'll have to think about it for my lunch time...

the gravitational force might be stronger, but there's less chance of breaking...

bilbo_pingouin

12:43 PM

ok... I think the key point is: which mechanism do you propose for collapsing?

a bridge collapses due to the perpendicular gravitational force from the Earth

overactor

@bilbo_pingouin what do you mean?

gravitational force along the length of the bridge

bilbo_pingouin

what about it?

overactor

if strong enough, it would cause shearing, no?

bilbo_pingouin

shearing is also the result of an external force... if your bridge is perfectly alined, why should it?

overactor

@bilbo_pingouin okay, suppose we rearanged the earth's matter into a cube, what would you say would happen?

bilbo_pingouin

12:51 PM

probably compress back into some sphere... is that what you mean?

you forget that you have forces in 3D instead of your bridge where you are essentially down to 1D

overactor

but there are imperfections

If the force is large enough, it will deform

bilbo_pingouin

yes, but on your bridge, and what you try to calculate, it is perfect, and you limit the study to 1D, and you've seen that the gravitation of one sphere is essentially affected by the nearest neighbours... not so much by the other spheres much further

in fact after the 3rd if you're chemist, the 10th if you're physicist, the effect of the following sphere will be negligible.

it is another history if you place your bridge on the Earth. Even if it's pointing upward. There, the accumulated weight comes to the lowest sphere. But it is an effect of the Earth

overactor

@bilbo_pingouin Yeah, but the spheres are inaccurate

Though I very highly suspect they paint a fairly accurate picture, I'd like to get some math behind it

overactor

1:35 PM

On which stackexchange site would this question best be asked:

Is silent flatulence actually more deadly?

biology, health, chemistry, some other se site?

bilbo_pingouin

chemistry or biology?

ok, consider a bridge of homogeneous material, regular and constant shape and very long in one direction. It has a base of surface $A$ (can be a circle, rectangle, etc.). You slice it in regular slices of thicknesses $d$. Regardless any other force, the gravitational force exerced by the $n$th slice on the very first is $$GmA\rho(1/n)$$

where $m$ is the mass of the first slice ($\rho Ad$)

overactor

Mathjax doesn't work in chat :(

bilbo_pingouin

it does

overactor

you're seeing fancy equations?

bilbo_pingouin

yes, you just need the right script ;-)

overactor

1:46 PM

@bilbo_pingouin aha

@bilbo_pingouin that only works for slices that are rather far away though

bilbo_pingouin

@overactor math.ucla.edu/~robjohn/math/mathjax.html

@overactor $n$ starts from 1

so the total gravitational effect all the $N$ slices has on the first part is $$GmA\rho \sum_1^N \frac{1}{n}$$

which does not converge

ah! Dammit, I was surprised also...

I forgot the squared!

overactor

I already calculated basically what you're calculating

bilbo_pingouin

so $$GmA\rho\sum_1^N\frac{1}{d^2n^2}$$

@overactor except I have no assumtion on the shape, as long as it is continuous

so it works for a cylinder... or a regular bridge... is the section stays constant

overactor

@bilbo_pingouin You're using Newton's law of gravitation, right?

bilbo_pingouin

yep

overactor

1:57 PM

That only works for very large distances, point masses or spheres

If you have none of those three, it's inaccurate

Try making the parts thinner and closer together

That's what I did at the point you're at

But replace the infinite sum with the value its value first

bilbo_pingouin

the point like, I got by having $d$ very small... and there you have your thinner part

overactor

oh, but then m is no longer the same

Try taking the limit of d -> 0

bilbo_pingouin

damn, I again screwed with the squares... $$GmA\rho\sum_1^N\frac{1}{dn^2}$$

since $m=Ad\rho$, $d$ essentially disappears

overactor

that's what I got

but you gotta be careful when taking the limit when d goes to 0

but it does work out, there is a limit and you can just drop all the d's

now here's the problem

the force stays constant, but the mass of the first section approaches zero

bilbo_pingouin

2:13 PM

ok, if you want to take the first one with a different thickness ($D$) you get to $$GmA\rho\sum_1^N\frac{d}{(\frac{D}{2}+(n-0.5)d)^2}$$

with $m=AD\rho$

with that you have no problem if $d\rightarrow 0$

but then it's harder to find the convergence and limit ;-)

overactor

That's quite clever, I expect that will converge nicely and be reasonably accurate

bilbo_pingouin

It does converge, indeed... with $n >> (D-d)/2$, we are left to $\sum 1/n^2$ which does. And the other is finite.

The problem that I have, is that this is the sum of the interaction between one slice and another (even with different width). But the slices also interact with each other... or maybe I'm just overthinking, and I should stop trying to do several things at once... :s

overactor

@bilbo_pingouin By taking the limit we actually have the exact force the rest of the road will exert on the first part I think

James

2:42 PM

Morning

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