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Galen

01:33

Is this question more likely to receive an answer on physics.se?

https://mechanics.stackexchange.com/questions/90204/does-a-log-linear-leak-tell-us-anything-about-the-properties-of-the-leak

1 hour later…

Silly Goose

02:51

i have survived sylow

3 hours later…

John Rennie

05:47

@Galen Hi Galen :-)

RewCie

Slept with my AC open, how I've cold

Chad morning everyone

John Rennie

@Galen The question isn't ideal for the PSE since we're not keen on questions that are working through a problem. However if you want to discuss it here that would be fine. Your graph looks exactly what I'd expect as I'd guess the rate of pressure loss would be proportional to the pressure i.e.

dP/dt = -kP

for some constant 𝑘

When we solve that equation we get an exponential decay as your graph shows. It's the same maths as for radioactive decay.

RewCie

I've tried a lot of daring things in my life, this is one of them

Using word instead of LaTeX

Galen

06:16

@JohnRennie Thank you for looking at my plot, and for the feedback on suitability for PSE. I appreciate your perspective. And we agree on the math! :P

I'm up for some discussion; thanks for offering. What's your impression of my speculation that the hole causing the leakage should be approximately constant in size if the pressure decays according to such an ideal exponential decay? My imagination suggests to me that if the hole was getting bigger (in terms of cross-sectional area) with respect to time that the dynamics would likely differ from dP/dt = -kP. Does that speculation make sense …

I guess how the dynamics differ would depend on the rate equation for how the cross sectional area of the hole changes.

John Rennie

Yes, as a general rule we'd expect the flow rate to be proportional to the area of the hole and also to the pressure difference across the hole.

Galen

Nice, that answers to questions at once! :)

two*

John Rennie

The actual details for anything other than some idealised cylindrical hole are complicated, but the overall result stays the same.

Galen

Right, differences in initial conditions and boundary conditions.

The rate constant can't reliably tell us anything about the (constant) size of the hole without knowing modelling the shape of the coolant system, right?

John Rennie

Yes, relating the rate constant to the geometry of the hole would be exceeding difficult for any but the most symmetrical holes. In general modelling fluid flows has to be done numerically with a biiiiiiiiiig computer unless it's a very simple system.

The flow is described by the Navier-Stokes equations and these are notoriously intractable.

Galen

06:25

Haha, okay. I don't think it is worth the effort for my car maintenance! :P I recall that being able to prove anything substantial about the solution set of the Navier-Stokes equation is a millenium prize problem. I guess the turbulence (chaotic flow) seems to be the tricky bit.

I'm going to head off. Thanks for helping me clarify my thinking on this subject, @JohnRennie

John Rennie

Yes indeed. No-one has won the million dollars yet! :-)

Bye :-)

6 hours later…

Mad

12:13

when it is talked about electron ions collusions or nuclear stopping power, electronic stopping power. What is meant with these collissions? Do they actually hit each other like biliard balls or is it the coloumb exchange force between the two?

1 hour later…

Feynman_00

13:16

No, we mean there is an interaction. In a classical picture you could think of Rutherford scattering for example

The collision you mention could be modeled using hard sphere potentials (which is not our case), Rutherford scattering is due to Coulomb potential

Physics Meta

13:55

Q: Why is my account blocked from asking questions?

I have asked genuine and very accurate question on this site and my question have been never downvoted except 1 and each and every question has been answered. If my questions had some problem they would never had been answered please see to it.

4 hours later…

Obama2020

17:30

Hello, I have asked a question on stack exchange physics.stackexchange.com/questions/734360/… do you think it’s understandable enough to get an answer

John Rennie

18:13

Warhammer vs Physics

For example:
Warhammer 40K: In the grim darkness of the far future, there is only war!
Physics: In the grim darkness of Chapter 11 of Goldstein, Poole, and Safko, there is only Chaos!

ACuriousMind

@JohnRennie lots of stuff missing there ;) e.g. both have a strange obsession with paths/ways associated with number eight (Physics, WH)

(in reality, in both cases likely to be a questionable appropriation of Buddhism :P)

Slereah

18:29

the chaos star is from Moorcock's Eternal Champion

it just symbolizes chaos by things going in every direction

The symbol of order is just a single arrow

"The origin of the Chaos Symbol was me doodling sitting at the kitchen table and wondering what to tell Jim Cawthorn the arms of Chaos looked like. I drew a straightforward geographical quadrant (which often has arrows, too!) – N, S, E, W – and then added another four directions and that was that – eight arrows representing all possibilities, one arrow representing the single, certain road of Law. I have since been told to my face that it is an "ancient symbol of Chaos" and if it is then it confirms a lot of theories about the race mind.

ACuriousMind

@Slereah Yes, but Khorne's association with the number eight and an eightfold path is a bit more than just the star

Slereah

I dunno, every chaos god has a number?

Someone had to end up with 8

due to en.wikipedia.org/wiki/Strong_law_of_small_numbers

Feynman_00

Why would someone write a book about Lie Groups adding an appendix about linear algebra and not on group theory? :P

ACuriousMind

@Slereah there's probably multiple steps here, it's perfectly possible that Khorne ended up with 8 first and then someone called his path the eightfold path as an allusion to Buddhism. WH (especially early lore) is often explicitly parodying real-world concepts or history so I don't feel this is that far-fetched

@Feynman_00 because you really don't need to know much about general group theory to understand Lie groups! Their entire structure is in the algebra, and so linear algebra seems a fine choice to me.

no point in knowing about Lagrange's theorem or Sylow groups (which is what a traditional intro to "group theory" would be about) or whatever when you're looking at Lie groups

Feynman_00

That's relieving

But I find it funny that the author feels the need to remind me what a vector space is but not what e.g. a group is :P