explain xkcd - User contributions [en]

Talk:3090: Sail Physics

2025-05-17T10:36:09Z

172.69.109.91:

After the last step, the sailors would then need to ground the boat to avoid being pushed in a circle, wouldn't they? [[User:Sophon|Sophon]] ([[User talk:Sophon|talk]]) 20:47, 16 May 2025 (UTC)

Note that for eastward wind, the boat will be propelled upwards, while the opposite is true for westward winds. This provides a basis for the functioning of airships and planes (Helicopters are more complicated, and additionally rely on their own magnetic fields) [[Special:Contributions/162.158.217.45|162.158.217.45]] 21:21, 16 May 2025 (UTC)
: Hence why you should always touch an earthing rod before approaching a helicopter, to avoid the magnetism pulling you into their rotors. [[User:Kev|Kev]] ([[User talk:Kev|talk]]) 03:11, 17 May 2025 (UTC)

Is this actually wrong? Wouldn't it still be ''a'' force on a sailboat, even if it's not the strongest? [[User:Smurfton|Smurfton]] ([[User talk:Smurfton|talk]]) 22:20, 16 May 2025 (UTC)

: I added some explaination on direction and magnitude of the lorentz force, maybe that will help - sga {{unsigned ip|172.68.234.227|22:33, 16 May 2025 (UTC)}}

The explanation states that of the four forces, only the electromagnetic force operates at the macro level. This is incorrect, as gravity is also directly observable by humans. There should also probably be a link to https://en.wikipedia.org/wiki/Airfoil to provide an explanation for how sails actually allow a boat to sail upwind. I recommend removing the remark about the poles potentially flipping in the future, as this is irrelevant. [[Special:Contributions/172.68.55.124|172.68.55.124]] 23:52, 16 May 2025 (UTC)

: What i meant was, for 2 objects at scales of humans =, maybe did not prase it well. In this case, it is the wind and the sail. Wind does not have a "mass" (the atoms most certainly do, but) we essentially have a pressure force, or momentum of wind, where instead of using the energy of atoms (and hence the mass) as given by kinetic theory is not used (that is random (as given by boltzman maxwell statistics)) and uniform (in the sense that for any direction, number of particles going against and towards is equal) and what we have is just pressure applied by a effective "group velocity" of the wind atoms. The gravity interaction between wind and boat, or the local waves and boat is negligible, and planetary gravity is not considered because that is not relavant for in plane motion. the pole fillping was added just for future proofing the article. I am sorry for the puns. I have rewwritten some parts, and reduced the part about pole flipping, and also added the average case scenario for the force, hope it is better now. - sga {{unsigned ip|172.70.143.75|02:37+, 17 May 2025}}
::That is one huge rambling paragraph, if it's (mostly) yours. I'm no stranger to ''writing'' huge rambling paragraphs, myself, but I gave up only a little way in on trying to make it read better. Grammatically, prosaically and with relevence.
::May I suggest that each 'frame' is treated to its own (shorter) paragraph, explaining what effect it tries to convey, what logic it individually tries to follow, but where it fails and what actual forces dominate a true example. (e.g. the hull-shape, including keel, helping convert roughly lateral sideways forces into forward ones against the water; those lateral ones having already been a conversion of largely head-on winds in the first place, thus two "almost up to 90 degree" redirections of force allow ''very nearly'' a 180-degree reversal of wind-blown movement. Feel free to discuss the comparisons and differences between 'flappy sail', though blown taught by the air, and an 'upright aircraft wing' solid design. ...See, told you I could ramble, but someone can surely do better at segmenting and summarising the basics of this.) [[Special:Contributions/172.71.178.32|172.71.178.32]] 08:32, 17 May 2025 (UTC)

This is super embarrassing to admit, but I came here to verify whether this was a serious thing or not. I had no idea how a sailboat sails against the wind. [[User:Catgofire|Catgofire]] ([[User talk:Catgofire|talk]]) 23:58, 16 May 2025 (UTC)
:You aren't alone - I think I was an adult before I understood tacking in the sailboat sense of the word. [[Special:Contributions/162.158.174.127|162.158.174.127]] 02:45, 17 May 2025 (UTC)
: I'm wanting to add in some wisdom about "science-y" explanations that appear to be sensible but are completely wrong, segueing into how generative language models appear to be far more reliable than they are. However this margin is too narrow [[User:Kev|Kev]] ([[User talk:Kev|talk]]) 03:09, 17 May 2025 (UTC)

hello [[Special:Contributions/162.158.42.97|162.158.42.97]] 03:58, 17 May 2025

Any chance we can add an explanation of how it *actually* works? [[Special:Contributions/162.158.216.174|162.158.216.174]] 10:03, 17 May 2025 (UTC)

The joke is that the most commonly used explanation for why flow over a foil generates lift - particles going one way have a longer way to travel than the other, which generates a difference in speed and therefore a pressure differential - is wrong.

1925: Self-Driving Car Milestones

2025-04-21T14:44:35Z

172.69.109.91: /* Explanation */

{{comic
| number = 1925
| date = December 6, 2017
| title = Self-Driving Car Milestones
| image = self_driving_car_milestones.png
| titletext = I'm working on a car capable of evaluating arbitrarily complex boolean expressions on "honk if [...]" bumper stickers and responding accordingly.
}}

==Explanation==
With the creation of self-driving cars, many new milestones are being found and/or solved thanks to them. Some are good, and some are downright weird. This comic lists some that have already been achieved, some that are being worked on and some that are facetious "milestones".

===Milestones that have been fully or partially achieved===

;Automatic emergency brakes
:This is another reference to how hard it can be to program human-obvious stuff (as in [[1425: Tasks]]). A self-driving car has to be able to distinguish a danger (cliff, person on foot/cycle/etc., other cars coming the wrong way/doing weird stuff) from the side of the road, the background, the other cars, or even a light pole safely standing on the side of the road. Then the car also has to decide the optimal response, taking into account weather conditions, road type and traffic - whether to turn aside, just slow down (as danger is not imminent), or actually do the strong brake. There are big potential advantages for self-driving cars if this problem can be solved: computers don't tend to panic as much as humans, would have faster reaction times and would have {{w|Autonomous_car#Safety|more reliable judgment}}.

;Highway lane-keeping
:Sometimes, especially on highways where road delimitations might be [https://upload.wikimedia.org/wikipedia/commons/thumb/1/11/Route_66_2073773569_7b3fae3b91_b.jpg/220px-Route_66_2073773569_7b3fae3b91_b.jpg faint or absent], or when lane markings could have faded away, a self-driving car programmed to pilot based on road markings would have issues holding to the correct side of the road. This is a bigger problem on highways than in cities, as cars move faster on highways, so the danger detection mentioned above might not manage to detect danger in time, while braking or avoiding the obstacle needs to be anticipated much more.

;Self-parking
:Already implemented in recent normal cars, this feature is important to remove the car from the road while not in use, and is sometimes considered a difficult maneuver for drivers to master, as it requires a good "feeling" of the car dimensions, as well as of distances and maneuverability of the car, and also information about surrounding barriers. The latter parameters, being easy to sense with radar and back-camera aide, are made more reliable with computers.

;Full highway autonomy
:The ability for a car to drive itself on a highway. As of 2023, there are [http://www.popularmechanics.com/technology/infrastructure/a13615577/self-driving-cars-lane-wisconsin plans] under consideration to set highway lanes aside for self-driving cars, but this milestone would require a car to be able to operate on a highway that also has human-driven cars, as well as wildlife, pedestrians, debris and other obstacles, should they enter the highway.

;First sex in a self-driving car
:This is not a milestone for the cars themselves, but just the age-old practice of having sex in cars, performed in a car that happens to be self-driving. Given the nature of human sexuality, it is probable that this had already happened at the time of this comic. Self-driving also allows the act to be performed while the car is in motion. The first public documentation of this milestone was published in May of 2019, as a video featuring coitus occurring in a Tesla Model X on autopilot went viral on PornHub.

;Full trips with no input from driver
:The main point of self-driving cars, allowing all humans within to act as passengers. As of 2023, self-driving cars require a human to be able to take over just in case, but any such trip where the human never actually took control would qualify for this milestone. However, there could be an additional joke here that the car is driving without human input ''including the destination.'' In this case, the car itself is choosing where to go, leaving the humans helpless.

===Milestones not yet reached===
;Full trips by empty cars
:A more complete version of the above, since with no humans present, no human can take control. This could be considered fulfilled by the {{w|DARPA Grand Challenge}} entrants, as the challenges are racing competitions of autonomous cars with no humans on board. Possibly a reference to [[1559: Driving]].

;Self-refueling of empty cars
:This would require either: a robotic fuel station, able to refuel cars with humans inside as well; an ordinary full-service fuel station (that is, one where the station's employee performs the refueling of the car) that happens to service a self-driving car with no humans aboard (which could be arranged as a publicity stunt); a specially designed fuel station that would allow self-driving cars to refuel by docking to it (likely to require fine control of the docking procedure that would render it unsuitable for more fallible human-driven cars); or, perhaps least likely, a robotic arm attachment on the car that would allow it to use a normal self-service fuel station. Currently [https://www.theverge.com/2015/8/6/9109027/tesla-model-s-snake-charger-elon-musk Tesla's robotic charging station] is the closest thing to this accomplishment. It is most certainly a reference to [[1559: Driving]].

===Facetious milestones===
;An empty car wandering the highways for months or years until someone notices the credit card fuel charges
:Cars are expensive enough that, were one to drive itself off and wander, some effort would be made to track it down. As this would require the self-refueling milestone, local fuel stations could be alerted to look for the "rogue" car—and in any case, whatever payment method is used to pay for the fuel would be traced.

;Cars that read other cars' bumper stickers before deciding whether to cut them off
:Another facetious milestone, implying self-driving cars might obtain the capacity to hold and act upon opinions that might override safety and efficiency of transit. This would be generally considered undesirable,{{Citation needed}} so this seems unlikely to actually happen, except perhaps as an unintended consequence of runaway self-learning.

;Autonomous engine revving at red lights
:Mimicking the human practice. This is often done by human drivers who wish to draw attention to their car and then speed off as quickly as possible once the light turns green, but is regarded by most as being a nuisance. As such, this is an unlikely goal for self-driving cars to achieve.

;Self-loathing cars
:This would require cars to become sentient enough to understand, and have negative opinions about, themselves. Depending on one's definition, though, self-diagnostic software might qualify, as they would be running on a car's computer and could express a negative opinion about the car (albeit normally limited to the context of the car needing maintenance). This may be a reference to {{w|Marvin the Paranoid Android|Marvin}} from ''{{w|The Hitchhiker's Guide to the Galaxy}}''.

;Autonomous canyon jumping
:Although it seems unlikely that a navigation routine would ever decide that jumping a canyon is part of an optimal route, a car could be programmed to jump a canyon as part of a stunt or show, with no human driver (or any other human aboard) at the time of the jump. It is questionable how "autonomous" such a car would be, though. Could also be a reference to the next point, with another popular setting in the discussions mentioned below: "should a self-driving car leave the road and drive into a canyon, which will kill the driver (and passengers), or stay on the road and kill others?". Possibly a reference to [https://electrek.co/2017/04/19/tesla-model-s-crash-cliff-save-life/ when a Tesla was driven off a cliff] and the driver and his passenger survived without injury. The car was not on autopilot at the time. This could also be in reference to the previous point with the idea that the car could develop extreme self-loathing and attempt suicide. Or it may be a reference to [http://www.imdb.com/title/tt0620882/ certain Knight Rider episodes.]

;Cars capable of arguing about the trolley problem on {{w|Facebook}}
:The {{w|Trolley problem}} is a well-known thought experiment in ethics, in which a person must choose between passively allowing several people to die or actively causing a single person to die. With the increasing likelihood of fully autonomous vehicles, there's been a flurry of interest in this problem, centered around what a vehicle should be programmed to do in such a case (for example, if avoiding a high-speed collision required running over a pedestrian). Randall seems to mock this debate by arguing that the true milestone would not be when the vehicle can make such a decision, but when it can argue about it on Facebook. This may refer to the idea that humans aren't capable of agreeing on a resolution to the problem, so expecting a vehicle to resolve it would be less reasonable than expecting it to be able to debate. On the day this comic was released the Youtube channel Vsauce posted a video, [https://youtu.be/1sl5KJ69qiA The Greater Good - Mind Field S2 (Ep 1)], where they tested people's reactions to the trolley problem in a fake situation where the subjects genuinely believed they were in a situation where they were choosing between saving five from an oncoming train by killing one on another track. Given such a coincidence, it is extremely likely that this milestone was added after Randall saw the episode.

;Evaluating arbitrarily complex Boolean expressions on "honk if [...]" bumper stickers and responding accordingly (title text)
:As with the cut-off milestone, this implies the development of artificial intelligence unrelated to the basic functions of a car, though still imitating human drivers' behavior. This joke is a reference to [[1033| a previous comic about honking and formal logic]].

==Transcript==

:Upcoming and recently-achieved
:'''Self-driving car milestones'''

:* Automatic emergency braking
:* Highway lane-keeping
:* Self-parking
:* Full highway autonomy
:* First sex in a self-driving car
:* Full trips with no input from driver
:* Full trips by empty cars
:* An empty car wandering the highways for months or years until someone notices the credit card fuel charges
:* Cars that read other cars' bumper stickers before deciding whether to cut them off
:* Autonomous engine revving at red lights
:* Self-loathing cars
:* Autonomous canyon jumping
:* Cars capable of arguing about the trolley problem on Facebook

==Trivia==
*The Trolley problem became part of the joke a month after this comic in [[1938: Meltdown and Spectre]]. And earlier, in [[1455: Trolley Problem]], it is even the entire subject.

{{comic discussion}}

[[Category:Self-driving cars]]
[[Category:Sex]]

Talk:2879: Like This One

2025-03-21T15:59:58Z

172.69.109.91:

i'm very confused what "this gas molecule" or "this skin microbe" is meant to be; it doesn't seem like there would contextually be an obvious specific instance of either of those classes? looking forward to seeing the conjecture given in the explanation when it settles down - [[User:Vaedez|Vaedez]] ([[User talk:Vaedez|talk]]) 02:48, 11 January 2024 (UTC)
:I believe it's referring to her holding her hand out to signify a (large number of) gas molecules. --[[Special:Contributions/172.69.34.49|172.69.34.49]] 02:55, 11 January 2024 (UTC)
::ahh, what she meant was "like these ones"--ok, I understand what both would mean now. - [[User:Vaedez|Vaedez]] ([[User talk:Vaedez|talk]]) 03:02, 11 January 2024 (UTC)
:::She's pointing at one molecule. Just because you can't pick it out of the mass doesn't change that. [[User:Nitpicking|Nitpicking]] ([[User talk:Nitpicking|talk]]) 03:55, 11 January 2024 (UTC)
:::: Indeed. And one wouldn't want to get the wrong idea about ''which'' molecule she might study. Obviously, there are a lot of N2 ones, and a few O2s, but they're not necessarily of interest. The odd noble gas atom (if that counts as a molecule-of-one) or CO2 would probably be the more useful, along with SO2 / O3 / other trace ones as what she might be indicating. [[Special:Contributions/141.101.99.79|141.101.99.79]] 05:34, 11 January 2024 (UTC)
:::::In my head-canon, she's using her stick-figure hand to point out an exceedingly long nitrogen nanotube that she's manufactured. Could be interpreted as a threatening gesture, I suppose?
:::::[[User:ProphetZarquon|ProphetZarquon]] ([[User talk:ProphetZarquon|talk]]) 16:00, 11 January 2024 (UTC)
: I think that's the whole joke - such statements are inevitably true, but at the same time essentially meaningless. [[Special:Contributions/172.70.86.140|172.70.86.140]] 16:49, 11 January 2024 (UTC)

I thought Ponytail probably studies the CO2 content of the atmosphere to track and predict climate change, but does not want to discuss it in a situation where people usually ask a question like "So what do you do?" (like a party). So she obscures the answer and makes her study field sound so mundane that Megan and Cueball will probably change the topic; whether they pick up the cue that when someone answers like that, they probably don't want to talk more about it, or whether they're bored out of asking more about some everyday gas molecules. [[User:Transgalactic|Transgalactic]] ([[User talk:Transgalactic|talk]]) 00:56, 19 January 2024 (UTC)

Other possible instances would include "Hominids" and "False vacuums". I was sure it was going to end with, "Cartoons like this one." [[User:Nitpicking|Nitpicking]] ([[User talk:Nitpicking|talk]]) 03:55, 11 January 2024 (UTC)
: Also, neutrinos would go on the list [[Special:Contributions/172.68.144.217|172.68.144.217]] 10:25, 11 January 2024 (UTC)

"I'm a researcher studying potential apocalyptic events..." [[Special:Contributions/172.70.90.115|172.70.90.115]] 09:40, 11 January 2024 (UTC)

Hmm. I’m a criminologist studying the behavior patterns of psychopaths.
::But wait, is the 'this one' referring to you, or me...? [[Special:Contributions/172.71.178.50|172.71.178.50]] 16:04, 11 January 2024 (UTC)

"I'm a researcher studying computer simulations…" (sadly, not actually the kind we are (maybe) living in but close enough) [[User:Brycemw|Brycemw]] ([[User talk:Brycemw|talk]]) 14:17, 11 January 2024 (UTC)

"I'm a researcher studying research topics..." [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 15:35, 11 January 2024 (UTC)

"I study logical paradoxes..." (¿"...like this one"?) [[Special:Contributions/172.69.43.180|172.69.43.180]] 15:45, 11 January 2024 (UTC)
:"I study self-referential statements..." [[User:Dextrous Fred|Dextrous Fred]] ([[User talk:Dextrous Fred|talk]]) 17:09, 12 January 2024 (UTC)

"I'm a biologist studying key turning points in human evolution... like this one!" "Man - that is the worst pick-up line..."[[Special:Contributions/172.70.90.71|172.70.90.71]] 16:20, 11 January 2024 (UTC)

"I study mathematical integers... like this 1." [[User:N0lqu|-boB]] ([[User talk:N0lqu|talk]]) 20:44, 11 January 2024 (UTC)
: I am not the judge of this contest, but if I were, you win! [[User:Terdragontra|Terdragontra]] ([[User talk:Terdragontra|talk]]) 20:03, 13 January 2024 (UTC) Word!!! [[User:Transgalactic|Transgalactic]] ([[User talk:Transgalactic|talk]]) 01:00, 19 January 2024 (UTC)

"I study human comments..." --Anonymous

"I study traditional pub signs, like The Swan" [[Special:Contributions/172.71.178.55|172.71.178.55]] 09:32, 12 January 2024 (UTC)
:Is ‘The Swan’ perhaps owned by [https://www.explainxkcd.com/wiki/index.php/Gnome_Ann Gnome Ann] (at least in this hypothetical)? [[Special:Contributions/172.68.1.131|172.68.1.131]] 14:59, 12 January 2024 (UTC)

"I'm an astrobiologist studying less-develooed civilizations... like this one" - Human Physics Padawan

"Skin microbes" seems a bit (intentionally?) obscure, especially since, it seems to me, the closest a modern microbiologist gets to an actual bacterium is its Illumina lane. "Skin lesions", however (warts, moles, calluses, liver spots, eczema/psoriasis, melanoma, yada) ... Of course, this might only occur to audiences of [ahem] a certain age (cue Rod Stewart's/Bob Dylan's "Forever Young" ...) [[Special:Contributions/172.70.207.186|172.70.207.186]] 21:51, 11 January 2024 (UTC)

”I’m a linguist studying languages”, and “I’m a student studying fictional works” also are kinda funny. [[Special:Contributions/172.68.1.130|172.68.1.130]] 15:01, 12 January 2024 (UTC)

== Do we really want to break down each bullet point? ==

We could probably do well to simplify it to just something saying the list contains things immediately surrounding the characters, part of their bodies, or intangible ideas commonly employed during normal conversation. It probably doesn't need to explain what sound waves are, for instance --[[User:Raviolio|Raviolio]] ([[User talk:Raviolio|talk]]) 15:34, 11 January 2024 (UTC)
:If breaking them all down, perhaps better a simple table rather than each 'hanging off' a bullet-point. But then we're more committed to breaking them ''all'' down (including Title Text) with potentially several paragraphs per 'explanation column cell'. (My preference, this moment, would be to restore the simple bullet-list then follow with the "air molecules" expansion below in regular prose, perhaps briefly zoom through the others in a single para to follow that, if not just wikilink those and leave to be checked at will. But that's just based upon what the current text might best be formatted as.) [[Special:Contributions/172.69.43.180|172.69.43.180]] 15:45, 11 January 2024 (UTC)
::The long exploration of exactly what interpretation of 'like' should be placed on Ponytail's remark that's currently attached to the bullet point seems rather peripheral to the joke. If anything ought to be explained, it's why each thing would (a) always be present (or at least, with rare exceptions like being in a spacecraft in deep space), but also (b) not be usefully identified by the remark.[[Special:Contributions/172.69.194.36|172.69.194.36]] 16:43, 11 January 2024 (UTC)

== Dreams like this one ==

I don’t think “I study dreams like this one” necessarily implies that the conversation itself is a dream.
It probably shall mean that the neurologist ''thinks'' they are in a dream, which would irritate other participants who don’t feel like they are part of a dream.

It could also imply that the neurologist is able to “show” a dream.
They could point towards an optical hallucination, being aware that it is not real, but not respecting the inability of the other participants to see it.

If I was the neurologist, it would just mean that I am currently dreaming while having this conversation in reality.
“This one” would mean “the current one”.
BTW how is it called if you dream while awake, separate/parallel to the reality? --[[Special:Contributions/172.70.246.181|172.70.246.181]] 08:25, 13 January 2024 (UTC)

::[https://en.wikipedia.org/wiki/Daydream Daydream?] [[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]]) 01:25, 16 January 2024 (UTC)