explain xkcd - User contributions [en]

Talk:2974: Storage Tanks

2025-02-08T19:00:51Z

172.70.207.159:

The symmetry of the truss intrigues me. Struts that are diagonal across the faces of the cuboids is normal, but is it a real thing to also use the body diagonal? Never seen that IRL, not sure if it makes sense from the statics. --[[Special:Contributions/172.70.247.82|172.70.247.82]] 22:16, 19 August 2024 (UTC)
: Struts as shown provide some left-right stability, but not as effectively as struts across the face would. They also provide some redundant front-back stability with the struts running along the faces. [[Special:Contributions/172.68.71.90|172.68.71.90]] 14:47, 21 August 2024 (UTC)
: I mentally modeled the flexibility modes, and it very much depends upon whether the verticals are solid (with their resistence to bending playing a big part alongside the incident horizontals'/diagonals' exactvmethod of attachment) or are just sections of rod between a suitable receiver-'node' at each junction.
: in particular, the strength of any one of the three 'boxes' (each level between adjacent horizontal cross-sectional perimeters) is somewhat less secure, as a single level can 'fold' sideways over each side's vertical-diagonal strut (along with the respective front/back horizontals, held 'square' by the internal cross-brscing). Only the continuation and linking with the other 'boxes' really guarantees any innate stability, and if each node is free-twisting then the likely first result of any failure is that the tower topples forwards and/or backwards as it folds up due to the unbraced facing and hindside quadrilaterals.
: But it does depend a lot upon the exact nature of the linkages (which can only be guessed at), and other failure-modes could involve node-slippage if they merely grip the cross-braces to the entirely top-to-bottom poles and there's potential for sliding there instead of primarily rotation (or over-stressed failure in any given length of rod).
: The support (or additional pressure) provided by the access staircase is also probably a factor. It could even be the most important bit in holding it up! ...if firmly anchored at the other end and robust enough in itself.
: I'd definitely add other diagonals (including opposite-type body-diagonals, perhaps tied to the existing one as they pass right across each other), just to be sure. The more the better, of course, but there's probably a limit through diminishing concerns. And too many diagonals primarily in a helical pattern could concentrate forces into a particular type of rotational failure if you also add too much brace-weight in doing so. [[Special:Contributions/172.70.163.120|172.70.163.120]] 15:07, 21 August 2024 (UTC)

Seems like a pretty menial job for the "head of security". I think he would delegate this to a security guard. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 00:47, 20 August 2024 (UTC)
: They may be head of a department of one.[[Special:Contributions/172.70.85.139|172.70.85.139]] 08:50, 20 August 2024 (UTC)
:: That's part of the joke, that the #1 concern of the Head of Security is calculus teachers wielding power drills for class demonstrations. [[User:Laser813|Laser813]] ([[User talk:Laser813|talk]]) 17:33, 20 August 2024 (UTC)

The explanation mentions there might be more complex calculus examples where the shape might not be a cylinder. I think some further explanation could be added that this does not change the pressure (hydrostatic paradox) but indeed change the rate of emptying the object. If differing cross sections are relevant at all. [[Special:Contributions/108.162.221.103|108.162.221.103]] 05:40, 20 August 2024 (UTC)
: Non-prismatic geometries are I think the ones being alluded to here, i.e a frustrum with the pointy end down will have a greater reduction in pressure for a given volume of flow towards the end than at the start, which may offset the reduction in absolute pressure. I've also seen examples where the flow rate is considered constant and the problem is to work out the fluid depth as a function of time, e.g. filling a pyramidal pool from a hose. [[Special:Contributions/172.70.58.4|172.70.58.4]] 16:44, 20 August 2024 (UTC)

Its the most difficult job in history, even the best workers couldn't stand 1 day as head of security.[[User:I HAVE NO NAME|I HAVE NO NAME]] ([[User talk:I HAVE NO NAME|talk]]) 05:55, 20 August 2024 (UTC)

I have to admit, I thought I knew calc as I had two semesters of it, but I had to look up what he meant by this. Ouch [[Special:Contributions/172.70.242.55|172.70.242.55]] 13:01, 20 August 2024 (UTC)student

If anyone could suggest something I can do for my class now that I can no longer drill holes in tanks, I'd appreciate the advice, thanks. [[User:Fephisto|Fephisto]] ([[User talk:Fephisto|talk]]) 16:18, 20 August 2024 (UTC)

Someone should do the math on the calculus problem as presented, as well as the algebra version. [[User:Laser813|Laser813]] ([[User talk:Laser813|talk]]) 17:33, 20 August 2024 (UTC)
: Randall, like all good mathematics textbook authors, left the problem as an exercise for the reader. Does this happen often enough to warrant a tag? [[User:Paddles|Paddles]] ([[User talk:Paddles|talk]]) 05:57, 21 August 2024 (UTC)
:: Yes... [[User:Transgalactic|Transgalactic]] ([[User talk:Transgalactic|talk]]) 10:10, 21 August 2024 (UTC)

Is there anyone else who thought the calculus teacher was abusing the tank as a model for the complex plane, demonstrating how to [https://en.wikipedia.org/wiki/Removable_singularity remove a singularity] from a holomorphic function by puncturing the plane? I wasn't confronted with that particular tank-emptying problem in high school, so my first encounter with "holes" in maths was in complex analysis. The title text was a mystery. [[User:Transgalactic|Transgalactic]] ([[User talk:Transgalactic|talk]]) 10:10, 21 August 2024 (UTC)

As a mathematician, I'm surprised I didn't know about this idea. (It's definitely not my field!) I actually thought the flow would be constant, an algebraic problem. Oh, I'm sure I saw these types of problems in Calculus (and I remember problems like this in Differential Equations), but I thought those were just to make the math more complicated, not based in reality... So is it the weight of the liquid remaining above the hole that is the source of the pressure (i.e., would it be the same if the top of the tank were open), or is it the air pressure in the tank as the volume of liquid decreases and volume of air increases? [[User:Mathmannix|Mathmannix]] ([[User talk:Mathmannix|talk]]) 11:08, 21 August 2024 (UTC)
:A sealed-top would change the dynamics (like trying to pour the contents of a 2 litre (or whatever the US equivalent is) pop/soda bottle, it will tend to 'glug glug glug' intermittently unless you: a) incline the bottle to allow an optimum amount lf free akr back into the emltying bottle or, b) initialise the up-ended emptying with a spin sufficient to create a 'waterspout' effect up through which the replacement air can (more) freely pass.
:Though there are other possible factors, in that example, including the potential pressure of any self-releasing carbonation pressure (e.g. giving the bottle a shake, or a foreign body, before releasing the 'pour') and/or squeezing/'milking' the soft plastic container strategically to create another form of pressurised expulsion.
:For the 'classical' problem, one should probably assume sufficient inward venting (either an open/part-open top or a second hole drilled near the top to effect this purpose) as well as a reasonably unexotic liquid (neither molasses, cornstarch-mixture, anything that is actually a very fine dry powder, anything that reacts significantly with/upon air, any liquid very close to its vapour-point nor ''specifically'' supercooled helium) or any additional elements (stirrers, baffles, spongey inners, inner membranes or the contents being a layered combination of imiscable liquids of different densities that may or may not react slightly all across the interface plane). Most things that aren't actually exotic (and even a few that are, and might warrant a warning /¡\) are close enough to water to treat as if just that, at least under the further assumption that we're working at or around Standard Temperature and Pressure. But a slightly different density, viscosity and surface tension (plus the nature of the container, e.g. extreme hydrophilic or hydrophobic inner coatings where water is involved) ''could'' (in combination) drastically change the actual outcome given enough of the right kind of simultaneous differences imparted. [[Special:Contributions/172.70.86.37|172.70.86.37]] 14:28, 21 August 2024 (UTC)
::We have these at my work: https://shop.snydernet.com/images/snyder-6370721n95402.pdf The viscosity is a huge deal, unless you can afford to waste a bunch of supply. [[Special:Contributions/162.158.186.248|162.158.186.248]] 08:29, 23 August 2024 (UTC)

In order to remove calculus from the scenario one needs a pressurization system that keeps Pair + Pliquid, constant at the hole. This requires sensing the height of the liquid surface and increasing the air pressure as the surface drops, the relationship depending on the density of the liquid. [[User:Mjackson|Mjackson]] ([[User talk:Mjackson|talk]]) 22:02, 22 August 2024 (UTC)

I wish my maths teachers back in the day had come up with any examples like this and I might have got a notion that calculus can be good for something after all, that there is an actual justification of learning it. I still might have failed in grasping it, mind you, but at least I'd have the decency to feel just a tiny little bit bad about it. I realise this is probably making me the odd one out here, but I felt I should mention it because it's linked to a fundamental problem of teaching - teaching anything at all, not just maths: most of the time you need to sell to your students the notion that knowledge and skills outside of your fields of interests, those that certainly don't relate to any career you have in mind for yourself, are valuable enough to justify the pain of learning them. You see, generations of "dumb", "lazy" students like I used to be myself have got it right on instinct: anything complex and abstract is literally painful to learn. Thinking hard in fact generally hurts, even if you pretend to yourself you like it (as I do, too, but what we really like are the results we come up with when we're done). Psychologists recently hammered this fact home in a large meta study [https://www.ru.nl/en/research/research-news/thinking-hard-hurts] [https://psycnet.apa.org/doiLanding?doi=10.1037%2Fbul0000443]). So with something as complex and abstract as calculus, you'll have to sell to them it's worth learning anyway, even despite a very real prospect of being able to live a perfectly happy and successful life without it, and if it's only of the weak basis of "it may still turn out to come in handy at some point". I'm a teacher myself, in case you're wondering, and if I taught maths and calculus and suchlike, transferring to it the same "signature" hands-on approach I'm somewhat known for using in geography, it'd be quite possible you'd see me drill an actual hole into an actual barrel (and likely make a show of installing a tap to make it reusable, too). [[User:PaulEberhardt|PaulEberhardt]] ([[User talk:PaulEberhardt|talk]]) 10:21, 24 August 2024 (UTC)

If the tank were sufficiently pressurized, they might end up having to mop up careless calculus teachers. The Hydraulic Press Channel has a series of [https://www.youtube.com/watch?v=sjS9HAtvBv0 videos showing the results of fittings popping off of over-pressurized tanks]. It did not bode well for any ballistic gel dummy heads that got in the way. [[User:These Are Not The Comments You Are Looking For|These Are Not The Comments You Are Looking For]] ([[User talk:These Are Not The Comments You Are Looking For|talk]]) 03:17, 26 August 2024 (UTC)
: Don't worry. Us teachers are professionals, because we get paid for it. 😁👍 [[User:PaulEberhardt|PaulEberhardt]] ([[User talk:PaulEberhardt|talk]]) 07:38, 29 August 2024 (UTC)

What if the tank pressure were randomized every few seconds? That way, neither calculus nor algebra teachers could use it as an example.

Talk:3045: AlphaMove

2025-02-02T11:08:55Z

172.70.207.159: Asked about quickest checkmate

Ask Tom Murphy VII to get on this [[Special:Contributions/141.101.99.103|141.101.99.103]] 22:50, 31 January 2025 (UTC)

I have attempted to run the proposed bot against itself — if I haven't made any errors, here are the resulting games:

Rounding down:
1. e4 e6 2. f3 f5 3. e5 g5 4. d4 d5 5. exd6 g4 6. d7+ Kf7 7. dxc8=N Ke8 8. fxg4 h6 9. gxf5 Kd7 10. g4 h5 11. fxe6+ Ke8 12. g5 Na6 13. h3 Nc5 14. h4 Ne7 15. Kd2 Ne4+ 16. Ke1 Nf5 17. g6 Nf6 18. g7 Ng3 19. gxf8=N Nge4 20. Ke2 Ng4 21. Kf3 Ngf2 22. Ke2 Nh3 23. Ke3 Nhf2 24. Nb6 Nh3 25. Na4 Nhf2 26. Nac3 Nxc3 27. Kxf2 Nxd1+ 28. Kf3 Qc8 29. c4 Ne3 30. Ke4 Nf5 31. Kd3 Ng3 32. e7 Nxh1 33. Kc2 Qb8 34. d5 Kxe7 35. d6+ Kf6 36. dxc7 Nf2 37. c8=R Ng4 38. Kd2 Nh2 39. Ke3 Ng4+ 40. Kd4 Nh2 41. Kd5 Nxf1 42. Nc3 Nh2 43. Nce2 Ng4 44. Nd4 Nh6 45. Nd7+ Kf7 46. Ndf3 Qd6+ 47. Ke4 Qd2 48. Nf8 Qd5+ 49. Ke3 Qd2+ 50. Ke4 Qd5+ 51. Ke3 Qd2+ 52. Ke4

Rounding up:
1. f3 f5 2. e4 f4 3. d4 e6 4. e5 g6 5. g3 fxg3 6. c3 g2 7. d5 gxf1=Q+ 8. Kxf1 exd5 9. Ke2 d6 10. Kd3 g5 11. Kd2 dxe5 12. Ke2 d4 13. Kd3 dxc3+ 14. Ke3 e4 15. Ne2 exf3 16. Ng1 f2 17. Nxc3 fxg1=N 18. Qc2 Kd7 19. Ne2 h6 20. Qa4+ Ke6 21. Qb3+ Ke7 22. Qb4+ Ke8 23. Qb5+ Kf7 24. Qa6 Kg7 25. Qa4 Kg6 26. Qb3 Kg7 27. Qb4 Kh7 28. Qb5 Kg7 29. Qa6 Nc6 30. Nxg1 Na5 31. Qb6 Kh7 32. Qb3 Kg6 33. Qb4 Kg7 34. Qb6 Kh7 35. Qb3 Kg6 36. Qb4 Kg7 37. Qb6

Rounding down code:
const { Chess } = require("chess.js");

const chess = new Chess();
while (!chess.isGameOver()) {
const moves = chess.moves();
moves.sort((a, b) => b.localeCompare(a));
const move = moves[Math.floor(moves.length / 2)];
chess.move(move);
}
console.log(chess.pgn());

To round up, swap the a and b in the sort function.

Both games end in a threefold repetition draw. The game with rounding down does, in fact, have 6 knights in it, so I believe he did code this to see what would happen.

[[User:Ohpointfive|Ohpointfive]] ([[User talk:Ohpointfive|talk]]) 22:52, 31 January 2025 (UTC)

To elaborate on the Tom VII point - this is the YouTube video that possibly inspired the comic: https://www.youtube.com/watch?v=DpXy041BIlA

[[Special:Contributions/141.101.98.179|141.101.98.179]] 22:55, 31 January 2025 (UTC)
:Specifically, it's the [https://www.youtube.com/watch?v=DpXy041BIlA&t=1483 Arithmetic Player at 24:43] set to ½. [[User:ChaoticNeutralCzech|ChaoticNeutralCzech]] ([[User talk:ChaoticNeutralCzech|talk]]) 17:52, 1 February 2025 (UTC)

Unfortunately for white, it's mate in 1 with Bb4# [[Special:Contributions/162.158.90.124|162.158.90.124]] 23:25, 31 January 2025 (UTC)

Even if white makes a different move, its still forced mate in one. RIP XKCD Bot. [[User:Redacted II|Redacted II]] ([[User talk:Redacted II|talk]]) 00:53, 1 February 2025 (UTC)
:Well, for most options. Queen to a4 puts Black in check, forestalling an immediate move to mate White; capturing the knight de-threatens enough squares around the king that Black can't check next turn without leaving an escape route. [[Special:Contributions/172.70.176.28|172.70.176.28]] 17:45, 1 February 2025 (UTC)

<s>Although it wouldn't change the outcome much (either by changing black's move or white's general options), I'm currently not understanding why Kd4 isn't on the list of options at this point in time. So long since I played serious(ish) chess, and the only reason I could think of is that it's probibited by some strict ortbodox game rule recognising the ''potential'' moving of the knight out of the way (in the next white move-cycle). But I'd have treated that later option as forbidden, as a revealing-mate. But, as I said, it's been a while, so maybe I'm just blind to something like a sweeping bishop-range that disbars this (much as the near knight, bishop and pawn disbars four out of the five moves).</s> ...darn, it's just clicked. That's the AlphaMoved white-knight's destination (before that, the black queen was entirely covering that square, and double-teaming one of the adjacent black-knight covered squares), I'd been thinking that was the piece's origin (with the empty highlighted square as its destination) until I'd finally read the highlighted movelist item properly and deciphered it as Knight To King Two (done), not the (intention of) Knight To King's Bishop One. So ignore the above. Although, just to note, for the Black Queen to have even achieved that position would probably have required at least ''one'' normally-sacrificial exposure to the deadly white Q/B/R pieces guarding the obvious entry, give or take the algorithmic development of their (and the "gateway pawns"') current positions. [[Special:Contributions/141.101.99.104|141.101.99.104]] 02:00, 1 February 2025 (UTC)
:Follow-up... As far as the black queen is concerned, I suppose she could have done d6, (x?)g3 then f2, in-between the other black and white moves made, largely safe from the white 'defence'. Or to d4 then f2, if white Queen's Pawn was shielding still. (Appears to have been taken, but it would have been bold to have done that with the queen, for a normally immediate pawn-queen exhange!) A bolder/more opportunistic set of moves than I would have tried, either. Even (unknowingly) against AlphaMove, I'd have been wary of the unconventionally developing white disposition actually being an idiot-trap (and I'm really not that far off being an idiot, insofar as chess). [[Special:Contributions/172.70.162.162|172.70.162.162]] 02:17, 1 February 2025 (UTC)

The explanation gives both O-O and 0-0 as notations for castling and then explains why 0-0 can never occur, even though O-O can be sorted pretty centrally. So, which is the correct notation? [[Special:Contributions/172.71.250.91|172.71.250.91]] 09:14, 1 February 2025 (UTC)
:According to the [https://ia802908.us.archive.org/26/items/pgn-standard-1994-03-12/PGN_standard_1994-03-12.txt pgn spec], section 8.2.3.3: they are capital Os and not zeros [[Special:Contributions/172.68.3.96|172.68.3.96]] 15:10, 1 February 2025 (UTC)

I'm pretty sure we're looking at a retrograde puzzle. [[User:Ohpointfive|Ohpointfive]] is onto something here, with the six knights on the board a strong indicator. The question is, of course, where is the joke? White plays Alphamove all along and must have started with e4 (rounding down) or f3 (rounding up). Both are consistent with the end position. So from my point of view, the joke is
* either that the "stronger engine" is not a strong engine at all but maybe the same algorithm, rounding up instead of down
* or that black doesn't win this position (in real chess, White is of course toast) because its algorithm is even worse
@Ohpointfive, could you run the two versions against each other? --[[User:Pganon|Pganon]] ([[User talk:Pganon|talk]]) 15:55, 1 February 2025 (UTC)

I created a playable version of this game in like 10 minutes using ChatGPT ;)

https://enn-nafnlaus.github.io/AlphaMove/alphamove.html

Git page here:

https://github.com/enn-nafnlaus/AlphaMove

-- [[Special:Contributions/172.69.144.163|172.69.144.163]] 17:52, 1 February 2025 (UTC)

I checked, castling and en passant both work. [[Special:Contributions/172.68.245.25|172.68.245.25]] 19:26, 1 February 2025 (UTC)

@Pganon certainly:
White rounding down vs. black rounding up:
1. e4 f5 2. f3 f4 3. d4 e6 4. e5 g6 5. d5 exd5 6. g3 fxg3 7. c4 g2 8. h3 gxf1=Q+ 9. Kd2 Kf7 10. Kc3 Ke8 11. Kc2 Kf7 12. Kb3 Ke8 13. Kc2 Kf7 14. Kb3 Ke8 15. Kc2
White rounding up vs. black rounding down:
1. f3 e6 2. e4 f5 3. e5 g5 4. d4 d5 5. f4 gxf4 6. h3 h5 7. h4 Kd7 8. Kd2 Kc6 9. Kd3 Kb6 10. Ke2 Kb5 11. Ke1+ Kb4 12. Ke2 Kb5 13. Ke1+ Kb4 14. Ke2 Kb5

The first game is quite exciting, with black at one point having a chance at checkmate in one, but alas too many available pawn moves drives the winning move Qxc4# far past the center of the list. The second game is much less exciting.

[[User:Ohpointfive|Ohpointfive]] ([[User talk:Ohpointfive|talk]]) 21:30, 1 February 2025 (UTC)

Here's a question: What is the quickest way to checkmate AlphaMove? Here's the quickest that I have found so far:
# f3 d5
# e4 d5xe4
# f4 e5
# g3 Bg4
# d4 Qxd4
# f5 e3
# f6 Qxd1#
Thus, we have mate in seven. This might be good to mention outside the comments section as a demonstration tha AlphaGo is not very good (not to mention failing to capture black's undefended queen), but a quicker checkmate might be possible, in which case we should mention that instead.[[Special:Contributions/172.70.207.159|172.70.207.159]] 11:08, 2 February 2025 (UTC)

3027: Exclusion Principle

2024-12-23T17:57:18Z

172.70.207.159: /* Explanation */ write for normal human consumption, please

{{comic
| number = 3027
| date = December 20, 2024
| title = Exclusion Principle
| image = exclusion_principle_2x.png
| imagesize = 264x336px
| noexpand = true
| titletext = Fermions are weird about each other in a standoffish way. Integer-spin particles are weird about each other in a 'stand uncomfortably close while talking' kind of way.
}}

==Explanation==
{{incomplete|Created by a COLLIDING ATOM. Do NOT delete this tag too soon.}}
In this comic, [[Randall]] lists the four {{w|fundamental forces}} of physics—gravity, electromagnetism, the strong interaction, and the weak interaction—then humorously adds a fifth force called "Electrons are weird about each other." This is a nod to how electrons cannot occupy exactly the same quantum state. The principle that underlies this is the {{w|Pauli exclusion principle}}, explained in [[658: Orbitals]], which says that no two electrons can have the same set of quantum numbers.

The idea behind Pauli Exclusion isn't really a conventional "force" like gravity or electromagnetism. Instead, it's a result of the fundamental quantum mechanical rules governing {{w|fermions}}, a class of particles that includes electrons. When combined with electromagnetism, it makes electrons repel each other more than mere electric charge would predict on its own. This phenomenon is sometimes described via the {{w|exchange interaction}}, which can be tricky to explain to non-experts.

Randall's joke is that physicists, frustrated with explaining the subtleties of quantum mechanics, have simply decided to create a "fifth force" to cover the weirdness of electrons. In reality, scientists cannot just invent new forces to patch up confusing behavior; they strive to describe how nature genuinely behaves, rather than rewriting the rules.

In the title text, Randall expands the idea from electrons to all fermions, which share the property of refusing to occupy the same spot, and contrasts them with {{w|bosons}}, which can happily share the same space. He humorously likens fermions to people standing standoffishly far apart, while bosons are like those who stand uncomfortably close while talking—an imaginative analogy for the fundamental differences in their quantum statistics.

==Transcript==
:[Inside the panel, there is an underlined header and a numbered list, with the fifth and last item in red:]
:Fundamental Forces
:1. Gravity 
:2. Electromagnetism 
:3. The Weak Interaction 
:4. The Strong Interaction 
:''5. Electrons are weird about each other''

:[Caption below the panel:]
:Big news: Physicists have finally given up trying to explain about the "exchange interaction" and agreed to just make the exclusion principle a force.

{{comic discussion}}

[[Category:Comics with color]]
[[Category:Comics with red annotations]]
[[Category:Physics]]