explain xkcd - User contributions [en]

Talk:999: Cougars

2026-05-15T16:23:34Z

82.132.238.68:

Lesson on sometimes flawed logic: It may seem obvious to you, but if XKCD thought about this a little more I hope he would recognize that we would make the greatest father any child could hope for. XKCD could teach his child something that no school or university ever could: to simply be inquisitive and curious about the world around him just as much as XKCD is himself, that and make sure that there are no cougars and raptors in 100 mile radius of his child. - e-inspired [[Special:Contributions/98.211.199.84|98.211.199.84]] 15:26, 27 February 2013 (UTC)
:That said, ''he'' probably doesn't have a filter. Which would be disastrous in other ways besides horror. Anonymous 16:08, 5 December 2013 (UTC)

In the UK '999' is the emergency services number, i.e. our version of 911. Could that be deliberate/relevant? [[Special:Contributions/172.71.242.207|172.71.242.207]] 02:54, 1 December 2023 (UTC)

Oh god it really is mostly children, I just checked. Well that sucks. [[User:RG|RG]] ([[User talk:RG|talk]]) 02:17, 15 May 2026 (UTC)
:Or, perhaps it's a good think? The alternative is that they're preferentially going after (and being successful at attacking) ''full-sized humans''.
:A problem for the children, who like to play outside, but something like "they mostly attack people binge-watching shows on Netflix" would suggest a far more sinister situation. And "victims are most often those trying to fill in their tax" would raise some odd questions. As would such injuries/fatalities overwhelmingly happening to commuters about to alight from their bus/tram/train first thing in the morning, or sitting down to eat their own lunch in the local McBurgerJoint. :P [[Special:Contributions/82.132.238.68|82.132.238.68]] 16:23, 15 May 2026 (UTC)

3239: Simple Machines

2026-05-15T16:07:50Z

82.132.238.68: /* Explanation */ If a list, does not need the Oxford Comma.

{{comic
| number = 3239
| date = April 29, 2026
| title = Simple Machines
| image = simple_machines_2x.png
| imagesize = 250x255px
| noexpand = true
| titletext = It's hard to decide which simple machine system to invest in. DeWalt makes a great lever and inclined plane, but I hear Milwaukee's wheel-and-axles are really good.
| wikidata = Q139738161
}}

==Explanation==
{{incomplete|This page was recently purchased from DeWalt, and we're still reading the manual. Don't remove this notice too soon.}}
There are various ways to use a {{w|mechanical advantage}} when applying a force to an object with a tool. Classically, there were considered to be six {{w|simple machines}} which, in combination, formed the basis of all tools: The {{w|lever}}, the {{w|wheel and axle}}, the {{w|pulley}}, the {{w|inclined plane}}, the {{w|wedge}} and the {{w|Screw (simple machine)|screw}}. These are often considered as idealised, abstract concepts in the study of {{w|mechanics}}.

{{w|Multitool}}s combine various tools into a single package, usually for reasons of portability. For example, the classic {{w|Swiss Army Knife}} combines various different forms of blade (which, in part, can act as levers and/or wedges, depending upon use) along with some non-bladed tools (such as the corkscrew, which naturally embodies the same forces as the 'simple screw').

Instead of combining simple machines to make a single tool, this comic suggests the existence of a multitool featuring all six simple tools individually, some of them with multiple purposes depending upon application. For example the lever and the inclined plane are both present via the same core rod.

The implication is that by having all the simple machines 'combined' in this way, this can serve as a universal tool, which could do the job of any other tool. In practice, though, it's hard to see many useful purposes this could be put to, since ''how'' you combine the various components and how they interact (or don't get in each others' way) is important for the function of a particular device.

As is often the case with multitools, there are obvious drawbacks to having this 'all-in-one' tool. The tools all have varying uses, some very different from one other, and you would be unlikely to find many devices in need of all the tools together all at once, so such a tool would be largely useless compared to its singular variants. Also, the tools come in many different sizes, meaning unless it has special adjustable sizes (which could well be impossible, to account for all the different sizes){{Citation needed}} the tool would be unlikely to be the right size to fit many features. As well as that, though [[Randall]] claims he can stop buying simple tools thanks to his all-in-one, in reality you often need more than one of the various tools for projects (particularly screws, of which there can be hundreds in a single project).

The title text is a joke about battery-powered tool ecosystems. {{w|Milwaukee Tool}} and {{w|DeWalt}} are two common American tool companies. The text notes that each company has advantages in certain specific simple machines, which makes deciding which brand to invest in for a whole system of simple machines difficult - presumably because each brand's machines are designed to work together, but would not work across brands. With battery powered tools, the batteries and the base motor units are often interchangeable between tools from a single brand (and are often purchased separately from the tools). Once you buy, say, a drill and batteries from one brand, it is more economical to buy a saw from the same brand, rather than the saw and batteries from a different brand.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
:[A rod with a square cross-section is shown sloping from top-left to bottom-right. At the bottom-right, it has a wedge tip. At the top-left, it is threaded left-handed and has a long nut on it. The nut has an eyelet where a rope is connected. The rope travels taut around a wheel on an axle connected near the wedge-end and then lies loose with a hook on the free end.]

:[Caption below comic:]
:I can finally stop buying simple machines now that I got an all-in-one tool with all six of them.

{{comic discussion}}<noinclude>

Talk:3243: Crystal Gazing

2026-05-15T16:03:17Z

82.132.238.68:

F1RST P0ST!!--[[Special:Contributions/158.123.138.25|158.123.138.25]] 17:52, 8 May 2026 (UTC)
:Not counting any posts made before the vale and/or veil of fire. [[Special:Contributions/150.221.155.241|150.221.155.241]] 22:10, 8 May 2026 (UTC)

Why is it "vale of fire" instead of "veil of fire"? [[Special:Contributions/174.20.245.60|174.20.245.60]] 18:06, 8 May 2026 (UTC)
:"vale" is a poetic term for a valley. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 19:06, 8 May 2026 (UTC)
:: That is indeed the definition, but seems less appropriate than "veil" which has the connotation of blocking/obscuring.[[Special:Contributions/174.20.245.60|174.20.245.60]] 20:59, 8 May 2026 (UTC)
::Not just a poetic term, but used in placenames (e.g. the "Vale of Evesham"), a vale generally more being a ''wide'' valley/flood-plain, framed by hills, rather than a 'mere' river-cut. But one of the more figurative/poetic terms I hear used is "vale of tears", a particularly sorrowful episode of life.
::(PPE: a 'veil' and a 'vale' of obscuration would each be rather different concepts. Veil is a thin barrier, vale a 'territory' of (iin this case) inpenetrability. I think the chosen wor is as good a term, if not better, than the other... But, I don't know if it's an intentional choice or merely a slipup that fortunately landed on a somewhat-synonymic term.) [[Special:Contributions/81.179.199.253|81.179.199.253]] 21:09, 8 May 2026 (UTC)
:I think there's definitely a "veil" pun going on there. "Beyond the veil" is something you can't see. [[User:Dogman15|Dogman15]] ([[User talk:Dogman15|talk]]) 02:46, 9 May 2026 (UTC)

Alternative the vale of fire for the heliophysists could just be the photosphere, a barrier in space rather than time.[[Special:Contributions/76.180.39.133|76.180.39.133]] 01:44, 9 May 2026 (UTC)

I'm not sure if "before the big bang" is a meaningful concept, at least from the inside of the universe. [[User:BunsenH|BunsenH]] ([[User talk:BunsenH|talk]]) 03:48, 9 May 2026 (UTC)
:Pretty darn sure that would be >18bya, 4.5bya would be the beginning of our start and planetary system[[User:Seebert|Seebert]] ([[User talk:Seebert|talk]]) 18:09, 11 May 2026 (UTC)
::Um, what's the complaint about, exactly? [[Special:Contributions/81.179.199.253|81.179.199.253]] 20:14, 11 May 2026 (UTC)
::: I think Seebert has assumed that BunsenH's comment was in reference to the aging of the Earth in the first paragraph, whereas it was actually related to a now removed reference to the Big Bang in the last paragraph. [[Special:Contributions/82.13.184.33|82.13.184.33]] 13:42, 12 May 2026 (UTC)

Surely the vale of fire for early universe cosmologists is the surface of last scattering? [[Special:Contributions/137.25.230.78|137.25.230.78]] 07:13, 9 May 2026 (UTC)

I'm fairly certain the 'vale of fire' is not always time-related, but also physical. Edited it to better reflect that.[[Special:Contributions/174.89.130.8|174.89.130.8]] 15:04, 9 May 2026 (UTC)

Is “vale” supposed to mean veil? {{unsigned ip|68.187.4.2|15:59, 11 May 2026}}
:See above... [[Special:Contributions/81.179.199.253|81.179.199.253]] 20:27, 11 May 2026 (UTC)

In the '''forward prophet of non-doom''' category, will the next comic be another [[:Category:Tuesday comics|Tuesday comic]]? [[Special:Contributions/2603:8081:9700:1224:0:0:0:2|2603:8081:9700:1224:0:0:0:2]] 05:29, 12 May 2026 (UTC)

Keep on misreading this as Crystal Glazing. Dunno what that implies but keeps on happening. [[User:RG|RG]] ([[User talk:RG|talk]]) 01:04, 15 May 2026 (UTC)
:It implies a [https://dwarffortresswiki.org/index.php/Window cut-gem window]?
:Either that or it imp ies the  ack of ' 's in a near y- egib e f ow of  egitimate  iteracy is  ess prob ematic for the  ikes of yourse f, as your interna ised  ogic supp ies them f aw ess y on your beha f. Un ess it go'''l'''es wron'''l'''g, '''l'''as abo'''l'''ve, '''l'''and st'''l'''arts p'''l'''ut'''l'''ting them'''l''' b'''l'''ack '''l'''in wher'''l'''e no'''l'''ne'''l''' were'''l''' mi'''l'''ss'''l'''ing i'''l'''n th'''l'''e fir'''l'''st '''ll'''in'''l'''st'''l'''a'''l'''nc'''l'''e'''l'''. In which case, you're hope ess y  o'''l'''s'''l'''t'''ll'''... ;) [[Special:Contributions/82.132.238.68|82.132.238.68]] 16:03, 15 May 2026 (UTC)

2809: Moon

2026-05-15T15:39:14Z

82.132.238.68: /* Explanation */ Where the captials are needed for the proper names of Earth(/Terra) and Moon(/Luna), rather than being earth(/soil) or moon(/natural satellite of a planet). Also qualified *what* is slowing (not, in that way, Earth in its solar orbit).

{{comic
| number = 2809
| date = July 31, 2023
| title = Moon
| image = moon_2x.png
| imagesize = 313x402px
| noexpand = true
| titletext = I mean, it's pretty, but it doesn't really affect us beyond that. Except that half the nights aren't really dark, and once or twice a day it makes the oceans flood the coasts.
}}

==Explanation==
The {{w|Moon}} is a celestial body orbiting Earth, first formed approximately 4.5 billion years ago - about 50 million years after the initial formation of the solar system. As of the date of this comic, the Moon is still orbiting the Earth{{Citation needed}} at an average distance of approximately 384,400 kilometers, or about 238,900 miles.

This comic points out how weird it is to have such an enormous celestial body near to us. The Moon has a radius more than one quarter of Earth's, and is around one eightieth of Earth's mass, and is so close that major surface features are visible, even with the naked eye, and much more clearly visible with even a simple telescope. Celestial distances tend to be so large that only truly immense objects can be seen without magnification, and even those tend to appear only as points of light to the naked eye. The second nearest body of notable size, Venus, is approximately 46.576 million kilometers away at its closest. The fact that there's "another world" that's close enough that humanity has always been aware of it, but distant enough that it couldn't be reached until a space program was developed, is a striking feature of Earth that we take for granted, only because it's always been that way.

While it's not uncommon for planets to have orbiting moons, no other planet in the solar system has a moon that's so large, in relation to the planet. Of the other rocky planets, only Mars has moons, and the largest of those is only 14 miles across.

Pluto and Charon are closer in size than even the Earth/Moon system, but their center of mass lies outside of Pluto. As such, they would actually be considered a {{w|Double planet|double(/binary) planet pair}}, had Pluto not been redesignated as a "dwarf planet". There is the possibility a term such as "double dwarf planet" could be adopted, at some point, as "double minor planet" is sometimes already used for binary asteroid systems. The lesser bodies of the Pluto-Charon system may then even be considered as circumbinary moons.

Other than this, Earth is the only accepted planet we're currently aware of that has a satellite that's so visible from its surface.

The title text sarcastically claims that, other than being "pretty", the Moon doesn't impact us, then subverts it by mentioning substantial impacts it has on Earth. Having such a large satellite so close has impacts that we take for granted only because we're used to them, but if they hadn't always existed, they'd seem unbelievable. One is that, for half the lunar cycle, the Moon reflects enough light to produce visibility at night. The other impact is tides, since the gravitational pull of the Moon is large enough to alter the surfaces of oceans, causing shorelines to shift on a daily cycle. The text mentions these dismissively, in a deliberate contrast with their huge significance. Moonlight alters the illumination cycle of the planet to a significant degree, which changes how both humans and other animals operate at night, especially before the advent of artificial lighting. Tides had major impacts on the development of life, continue to affect ecosystems, and play an essential role in our ability to interact with the oceans. If someone from a planet without such a large moon were to observe these impacts, they'd likely be shocked and amazed by them, but we barely notice them. Another impact is {{What If|26|leap seconds}}, since the gravity of the Moon pulls on the Earth, ever so slightly slowing the rotation of the Earth down

The comic [[3135: Sea Level]] is very similar to this one, but it starts with noting how strange and SciFi the tides on Earth are.

==Transcript==
:[Ponytail is pointing and looking up to the left, while Cueball behind her looks the same way.]
:Ponytail: That thing hanging in the sky is a second nearby world. It's close enough that you can see its surface as it passes overhead.
:Cueball: Wow. Isn't that ... weird?
:Ponytail: I dunno, it's just always been there.

:[Caption below the panel:]
:If it didn't exist, the moon would sound like such an outlandish sci-fi concept.

==Trivia==
*Earth's moon can be considered weird for additional reasons.
**It is by far the largest and most massive moon relative to the planet it orbits.
**Our moon is the only moon in the solar system to not have a proper name, not even a jumble of letters and numbers. In English it is simply given the proper name of "the Moon" (capitalized), being the ancient archetype for all other moons discovered since the time of Galileo, although it can also be described by other titles such as "Luna" (directly taken from from Latin mythology/astronomy).
**It is almost exactly the same apparent size as the Sun in the sky which at various times enables both total solar eclipses (for which it needs to be close/large) and annular ones (for which it must not be ''too'' close/large). Much earlier in history it was too close to do both and much later it will gradually drift too far away to do so – making it additionally a temporal coincidence that humanity gets to witness it as we are so used to seeing it.
**There are even a couple of hypotheses that think that to get protein shaped right for life, the tides were needed, and that to evolve for living on land the tides are needed.
{{comic discussion}}

[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Astronomy]]

Talk:3244: Pullback Drive

2026-05-15T15:29:33Z

82.132.238.68:

Is that supposed to be Elon Musk? {{unsigned ip|185.114.120.233|09:24, 12 May 2026 (UTC)}}

There are toy cars that work like this, or that use a flywheel to store energy in a similar way, for example the Fisher-Price Rev 'N Go Stunt Vehicles. The salesman is offering a full sized car on the same principle. The toys don't go very far. Neither will the full sized car, though he implies it will go "far" before stopping. He doesn't offer any practical way to rewind the spring. [[Special:Contributions/2A12:F43:1462:CC00:583C:B3A7:2A0B:2140|2A12:F43:1462:CC00:583C:B3A7:2A0B:2140]] 09:56, 12 May 2026 (UTC) dww
:Pull-back and Rev-up toys work significantly differently (though a pull-back toy ''may'' have a flywheel effect, it doesn't usually rely on this). Both are, of course, ways in which a child puts their effort into a much smaller vehicle that then expends that effort into forward motion (from my childhood, there were 'friction-toys' or even the Evel Knievel Stunt Bike, on one hand, and things like the Penny Racers, on the other).
:The Rev'N'Go type perhaps ''can'' be far more indefnitely charged with energy, upon being released (barring mechanical failures and stripping/melting the plastic cogs), but would not give you the described Clicking that the comic says is happening, which is a sign of a sprung-toy with basic overwind-protection designed in.
:Also, riding a (for example) full-sized Evel Knieval flywheel bike and applying the brakes (assuming they ''could'' stop it in time!) would probably just stop it, and leave no more energy to move off again (unlike the spring-powered car, halted before too unwound). I suppose you ''could'' make the brakes disengage the drive from the still-running flywheel, then 'clutch back on' when you released them again, but still not something that mofe pulling back at the factory is going to help reduce your range-anxiety with. [[Special:Contributions/82.132.221.157|82.132.221.157]] 16:00, 12 May 2026 (UTC)

Energy storage. The devil is in the detail, and the magnitudes. It turns out a rubber spring (aeroplane elastic) stores rather more energy weight for weight than a steel 'clockwork' spring. However batteries, and hydrocarbons, store orders of magnitude more. This subjectwould be good for one of Randall's 2D graphs, plotting use case against energy stored. For instance, a diver's harpoon gun uses a pull-back mechanism quite effectively. {{unsigned ip|82.19.218.32|10:22, 12 May 2026 (UTC)}}

I italicized the "or" in the first section of the transcript [[User:SomebodyElse|SomebodyElse]] ([[User talk:SomebodyElse|talk]]) 11:09, 12 May 2026 (UTC) SomebodyElse 12:08, 12 May 2026 (UTC)
:Isn’t it also bolded?[[User:Commercialegg|Commercialegg]] ([[User talk:Commercialegg|talk]]) 12:51, 12 May 2026 (UTC)
::Looks like it is. :) [[User:SomebodyElse|SomebodyElse]] ([[User talk:SomebodyElse|talk]]) 18:09, 12 May 2026 (UTC)SomebodyElse 17:08, 12 May 2026 (UTC)

Is the mention of worries about gas prices a reference to Trump's war on Iran? [[User:SectorCorruptor|SectorCorruptor]] ([[User talk:SectorCorruptor|talk]]) 14:52, 12 May 2026 (UTC)
:Almost certainly. I've added it in. --'''''[[User:DollarStoreBa'al|DollarStoreBa'al]][[User_talk:DollarStoreBa'al|'''''converse''''']] 14:38, 12 May 2026 (UTC)

Does this count as a [[:Category:Tuesday comics|Tuesday comic]]? Not sure when it went live but it hit explainxkcd at 0900 UTC, which was 2AM Tuesday morning California time. It was still Monday in Hawaii (UTC-1000) though. [[Special:Contributions/64.201.132.210|64.201.132.210]] 15:18, 12 May 2026 (UTC)

Probably the real vehicle getting most close to the pullback drive is the Gyrobus: https://en.wikipedia.org/wiki/Gyrobus {{unsigned ip|2a02:3100:8bac:fe00:1e1b:dff:fe9f:401d|20:40, 12 May 2026}}

I'll let another editor handle the writeup and citations, but here are some order-of-magnitude comparisons: The springs actually in your car's engine store a few joules. A garage door spring might store a few kilojoules. An [https://www.shibata-fender.team/files/content/products/SPC-Cone-Fenders/Product_Information_SPC_Fenders.pdf eight-ton chunk of rubber] can absorb 5 megajoules, and a single gallon of gasoline stores >120 megajoules. Even if you have some incredibly machinery to get that energy out, there's several orders of magnitude between (the spring energy you can store inside a car) and (the spring energy needed to make a car go even one mile). {{unsigned ip|206.209.15.112|21:02, 12 May 2026}}
:You can make springs out of petrol? [[Special:Contributions/2001:569:FBCA:1700:986:CE3B:3243:855|2001:569:FBCA:1700:986:CE3B:3243:855]] 00:47, 13 May 2026 (UTC)

Just reading this article and seeing this sentence:

> This is technically true, but cats that run on petroleum or atomicity have the advantage of their energy supply being refillable, while this pullback cat seemingly does not (without another factory-style 'pull back' facility).
[[Special:Contributions/82.196.111.48|82.196.111.48]] 19:06, 13 May 2026 (UTC)
: I think you needed to paws and read those clawses again. [[Special:Contributions/82.13.184.33|82.13.184.33]] 08:30, 14 May 2026 (UTC)
: I mean people intentionally misspell cats as cars all the time, maybe this is just the reverse? [[User:RG|RG]] ([[User talk:RG|talk]]) 00:51, 15 May 2026 (UTC)
::It'll be a direct call-back to the comic [[1288: Substitutions]] (and perhaps followups). Which some people have actually installed a filter in their browser to actually make 'work' for all web-browsing, or just some of it (e.g. this site). And I've seen that then cause confusion, but it's often Poe's law whether any particular example of that is real or pretended. [[Special:Contributions/82.132.238.68|82.132.238.68]] 15:29, 15 May 2026 (UTC)