3047: Rotary Tool

Welcome to the explain xkcd wiki!
We have an explanation for all 3195 xkcd comics, and only 60 (2%) are incomplete. Help us finish them!

Latest comic

Go to this comic explanation

Truly Universal Outlet

|< < Prev #3186 (December 26, 2025)

Title text: Building Inspectors HATE This One Weird Trick

|< < Prev Random Explanation

Explanation

This is one of 60 incomplete explanations: This page was created by a 110 VOLT BRITISH PLUG. Need to add pictures of the different outlets and maybe even overlay them onto the comic?. If you can fix this issue, edit the page!

This comic shows a layout for a universal outlet which would theoretically fit any mains power-plug. Throughout the world, countries and regions have their own standards for outlets, including their shape, contact amount, and voltage. When traveling, or otherwise using devices from other countries, it is often necessary to have an adapter to connect one type of plug to a different outlet.

The comic shows an outlet with fifteen sets of holes merged together, so that any of those plug types might fit. In reality, it's possible that a plug may not be held securely, and it may fall out or lose contact. For example, the hole for types D, M, and O at the top of the outlet has three distinct holes, some of which are entirely contained within others; a prong for a smaller type would not make contact with the walls (without particularly spring-loaded contacts). Different outlets can also mean different voltages, which can risk damage if devices do not account for it. Although universal plug adapters actually exist, none of them are as 'universal' as the one shown in this comic, most likely due to aforementioned safety concerns.

Also the comic seems to misrepresent type E sockets - it seems like Randall wasn't aware of (or ignored) the fact that type E sockets has a grounding pin that protrudes out from the socket, and rather represents it as if it were a hole in the socket instead. In reality it would be difficult to make a socket that safely grounds type E plugs without being simultaneously incompatible with a large number of other plugs that aren't designed to accommodate the grounding pin, probably requiring the prominent socket-pin to be a spring that retracts far into the socket when pressed by a plug's ground pin.

The comic also seems to not notice the lack of grounding for full compatibility with F plugs. This leaves them in the same state as type E above. This could be fixed by adding the extra pins for grounding. Given that most plugs in E and F regions are compatible with both standards (CEE 7/7) and have the E ground connected to the F ground through a front plate bigger than the hole for the E standard, it would be theoretically possible to make a mostly universal plug, with the exception of pure CEE 7/5 Schuko and some pure French-style CEE 7/6 that don't have the external metallic plate, but both of those are vanishingly rare, phased out by the CEE 7/7.

The title text references the classical clickbait format "<organization/role> hate this one weird trick," implying <organization/role>'s services will be no longer needed if the trick works out as it claims to, and therefore (according to the clickbait) they do not want you to find out about the trick. In this case, however, building inspectors likely hate the design solely because of its grotesque safety problems.

While this comic is not part of the Cursed Connectors series, it does follow a similar theme of unorthodox or dangerous ways to make electrical connections.

Transcript

This is one of 33 incomplete transcripts: Don't remove this notice too soon. If you can fix this issue, edit the page!

[A diagram of an electrical outlet is shown, merging the holes of many international outlets. Dashed lines indicate individual standards' holes, which are labeled by their corresponding letter from A to N. The entire outlet is the combined area of these holes.]

Wiring tip: To make your building friendly to international visitors, cut holes in your outlet plates to make them compatible with all fifteen IEC plug types.

Trivia

• This comic was released on Boxing Day during Christmas of 2025, but makes no reference to Christmas.
  • The previous comic, released on Christmas Eve, 3185: Sauropods also made no reference to Christmas.
  • This thus marks the second year on a row without any Christmas comics released during those days, see this trivia from the comic 3029: Sun Avoidance released on Christmas Day in 2024 (first time such a day was not given a Christmas comic).

  Add comment        Create topic (use sparingly)       Refresh 

Discussion

How come it's at 0.017 RPM for a minute?? and yet 1 RPM for a second? pls fix this randall Midnightvortigaunt (talk) 18:01, 5 February 2025 (UTC)

Its 0.017 RPM for the minute hand. The minute hand revolves once per hour or at 1/60 RPM ≈ 0,017 RPM --172.71.148.59 18:14, 5 February 2025 (UTC)

Ohhh that makes sense I didn't think about it like that Midnightvortigaunt (talk) 19:27, 5 February 2025 (UTC)

Mr.Dude (talk) 17:20, 7 February 2025 (UTC) I wonder what torque is needed to launch the average backyard telescope worthy of a tracking mount at Mach 8 given standard state pressures and temperatures of perhaps average conditions found in Randall’s back yard.

How come the comment above is invisible to me? 172.68.245.229 18:03, 5 February 2025 (UTC)

Possibly because people indented with spaces rather than with colons? 162.158.79.77 19:40, 5 February 2025 (UTC)

72 RPM for a record player...? 162.158.74.25 18:08, 5 February 2025 (UTC)

I could only find 78 RPM disks in the german wikipedia. 172.70.114.56 18:41, 5 February 2025 (UTC)

I came here to make the same comment: 72 is most probably a typo. The old records (at this date, very old, since the transition to vinyl records was 1948 to 1958 (in the US)) were 78 rpm, not 72 rpm https://en.wikipedia.org/wiki/Phonograph_record Rps (talk) 19:30, 5 February 2025 (UTC)

72 is (for example) relevent to font sizes (size 1 = 1/72 of an inch, size 72 = 1 inch), which might therefore have envaigled Randall's head for numbers by a different route, and got him confused. Conceivably he has had to deal with playing old 78s, but probably not for a long time... even the retro-revival of vinyl, recently, has probably not had quite so many old old records released to fill such nostalgic needs. So an easy brain-fudge/thinko to trip over on. 162.158.74.48 00:54, 6 February 2025 (UTC)

There used to be a record label call 72RPM records. 172.69.229.146 (talk) 19:07, 5 February 2025 (UTC) (please sign your comments with ~~~~)

We need one of those tables in here. DollarStoreBa'al (talk) 18:37, 5 February 2025 (UTC)

I made a change to the explanation that all of these numbers are realistic because, I checked out the speed of dental drills and they really do rotate that fast. I haven't checked out all of the other tools, but I suspect that they are also accurate. If you find that any of them are misstated, please correct my correction. Rtanenbaum (talk) 22:38, 5 February 2025 (UTC)

TABLE REQUEST When someone uploads a table, I'd like to recommend a second column for the frequency / reciprocal of the speed. "0.000000000073 minutes" is one every 13.7 billion minutes, or ~26,000 years. Thanks! 172.70.46.107 20:20, 5 February 2025 (UTC)

Me again. Should the column header "revolution time" be "rotation time"? In every instance, the axis of motion is within the object itself; even the second/minute/hour hands go around the axis. 141.101.76.73 16:41, 6 February 2025 (UTC)

TRIVIA 16 2/3 RPM phonographs were used for some voice-recorings back in the day. 172.68.26.24 21:01, 5 February 2025 (UTC)

My parent's old record player (60's, probably) had 4 possible speeds: 16, 33, 45, 78. By the early 80's the current ones only had 33 and 45. Rps (talk) 16:59, 7 February 2025 (UTC)

Album goes back to stacks of 78s. A symphony or opera would be 2, 3, 4 or more disks. They were bound like a photo-album with a leaf for each disk. "78" wasn't "standardized" until the format was fading. 3600-rpm motor and 46-tooth gear is incomplete (one tooth gear??) Early discs were from 60 to 130 rpm. Users would adjust speed by ear (also to ease pitch-matching for karaoke). Only as LPs arrived did someone invent the number "78.26 rpm" (no recordplayer and few lathes of the period were near that accurate). --PRR (talk) 02:34, 6 February 2025 (UTC)

Indeed, my parents had a large collection of old records and at least one had a speed marking of 80rpm.--172.68.186.43 09:17, 6 February 2025 (UTC)

With wind-up players, a lot of them started off playing at one speed and ended playing at a completely different one anyway...172.68.186.50 09:43, 6 February 2025 (UTC)

I suspect there's not many consumers needing a Uranium Enrichment Centrifuge... at least outside of a few countries in the Middle East. --172.70.58.6 08:50, 6 February 2025 (UTC)

Might face some regulatory / export license issues too.172.70.86.129 11:34, 6 February 2025 (UTC)

I feel like there was a lost opportunity to have Dr. Who's Sonic Screwdriver on the list. Maybe the rpms are unknown.162.158.159.107 13:05, 6 February 2025 (UTC)

The table says that 0.00070 "seems off; a sidereal day is 23.93 hours". That's just because (like all of the other settings) 0.00070 is quoted with only 2 significant digits. Every period between 23.64 and 23.98 hours would round to 0.00070 RPM. 162.158.134.199 13:58, 6 February 2025 (UTC)

The question I have is: why are dental drill speeds so high? 172.70.247.92 17:21, 6 February 2025 (UTC)

"why are dental drill speeds so high?" It hurts less. (Are you old enough to remember routine use of belt-driven dental drills?) You can cut a given amount of material (wood, steel, tooth) quickly with heavy force or high speed. Neither is really fun, but hi-speed is generally preferred. --PRR (talk) 19:08, 6 February 2025 (UTC)

Although some materials behave badly to heat (either work-hardening, for some alloys, or melting/burning, like plastics) and that's why variable-speed hand-drills/etc usefully have low speeds (for essentially the same force, when that's done via reostat rather than an actual gearbox). On the few occasions I've had my teeth drilled, I'm pretty sure I've detected the pungent smell of fried tooth-fragments, but it was nothing like as strong as smelling my own nose-flesh being burnt one of the times I had it cauterised to try (and fail) to prevent excessive nosebleeds. 172.69.79.139 21:15, 6 February 2025 (UTC)

The latest NMR CPMAS probes send their rotors to go at 9.6 Mrpm, M=mega. [1] --172.69.109.172 21:56, 7 February 2025 (UTC)

Should we list the rotor diameters to achieve the mach 8 speed mentioned in the title text in the table? I don't think that we should. guess who (if you desire conversing | what i have done) 06:01, 24 February 2025 (UTC)

I (obviously since I worked it all out) think it is in the spirit of the ridiculous idea of the comic and XKCD generally to do these calculations. That said, I'm getting different numbers than your update to make it Mach 8. Denver87 (talk) 16:21, 24 February 2025 (UTC)

I get the following: 4,799au, 74,866km, 37,733km, 3,144km, 52.4km, 1,588m, 1,165m, 728m, 175m, 34.9m, 21.0m, 149.7cm, 87.3cm, 174.7mm. Denver87 (talk) 16:21, 24 February 2025 (UTC)

Happy to share calculation notes, but here's the example for the dental drill: 300,000rpm = 5,000 rps; diameter of: 174.7mm --> circumference of: pi * 174.7mm = 548.8mm; 548.8mm * 5000rps = 2,744,000mm/sec = 2744m/sec; Mach 8 = 8 * 343m/sec = 2744m/sec. Denver87 (talk) 16:21, 24 February 2025 (UTC)

If you agree with the calculations, one of us can at least update it. Denver87 (talk) 16:21, 24 February 2025 (UTC)
        Add comment

Is this out of date? .

New here?

Last 7 days (Top 10)

Rank Score Pages Changes Username 1 23 19 23 TheusafBOT 2 15 2 42 Firestar233 3 11 7 11 Lp0 on fire 4 9 5 9 R128 5 9 5 9 Kynde 6 9 6 8 FaviFake 7 8 4 9 RadiantRainwing 8 7 2 8 Barry Margolin 9 6 2 7 Vaedez 10 6 3 5 TheErgster

Lots of people contribute to make this wiki a success. Many of the recent contributors, listed above, have just joined. You can do it too! Create your account here.