1395: Power Cord

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
Power Cord
In this situation, gzip /dev/inside to deflate, then pipe the compressed air to /dev/input to clean your keyboard. Avert your eyes when you do.
Title text: In this situation, gzip /dev/inside to deflate, then pipe the compressed air to /dev/input to clean your keyboard. Avert your eyes when you do.


In this comic, we see Beret Guy walking in from the left, as Cueball is sitting on a couch, typing on a laptop on his lap, with its power cord unplugged. Instead of connecting it to the wall socket, Beret Guy picks it up and blows air into the loose end of the cord, as if inflating a balloon — and the laptop inflates, along with the "power brick" that is on the cord. It then floats away, making Cueball grab for it as Beret Guy casually walks away. (See an instance where Cueball inflates something in a similar unexpected way in 1798: Box Plot).

It is not possible to inflate a laptop like this[citation needed], and (with rare exceptions) it is not possible to inflate anything by blowing down a power cord. Beret Guy has previously demonstrated several supernatural abilities, for instance with power cords, such as in 1293: Job Interview.

In general, human breath should not be buoyant enough to lift much in an atmosphere of ordinary air (see Trivia section below for details). There is a standard cartoon convention that inflating something with breath nonetheless makes it lighter than air. Also, given Beret Guy's many manifestations of inexplicable phenomena, it is not too far fetched to believe his body is, in fact, expelling some form of lighter-than-air gas, similar to the character Rigel on Farscape who could "fart helium".

The title text involves some jokes on Unix systems. On Unix, everything is a file; even most of the hardware can be referenced by a (virtual) file. These virtual files usually are in /dev or another virtual filesystem like /sys or /proc. While /dev/input really exists and points to the input system (mice, keyboards, gamepads, etc.), /dev/inside doesn't. gzip is a common tool to compress files. The first joke is to compress the air inside the laptop (with the command gzip /dev/inside) in order to deflate the laptop back to normal size. It is a pun with the literal meaning of "deflate", which is also the DEFLATE algorithm used by gzip (compressing files is also called "deflating"). Another joke is "piping", the act of using the output of one operation as the input to another. As the output of the gzip command would be compressed air, a physical pipe could be used to direct the air somewhere useful. The output of a command can also be redirected to a file. Since the hardware is a file, the suggestion is to direct the air to /dev/input (which, in this case, means the keyboard, but would actually be a directory on real system, which can't normally be piped into) to clean it, similar to "compressed air" dusting cans. The complete command would be gzip /dev/inside | /dev/input. As this might cause a spray of unpleasant detritus (compare 237: Keyboards are Disgusting), the reader is advised to avert their eyes.


[Beret Guy enters to find Cueball on a chair typing on a laptop. Cueball's power cord is unplugged from the wall.]
Cueball typing: Type type
[Beret Guy picks up the power cord. Cueball continues typing.]
Cueball typing: Type type
[Beret Guy blows into the plug end of the cord. The laptop abruptly inflates and Cueball jerks back.]
Beret Guy: PBBBBT
Laptop: FOOMP
[Beret Guy walks away, leaving Cueball climbing up his chair to retrieve his inflated laptop which is now floating away.]


The only chemical difference between dry air and dry exhaled breath is the conversion of oxygen (molecular weight = 32) to carbon dioxide (MW=44), not counting substances in such low concentrations that their effect on the average molecular weight of the air (MW=29) is negligible. A change of concentration of the CO2 from 0.04% to about 4% is typical. This increases the average molecular weight. However, exhaled breath is also usually much more humid than air, increasing the concentration of water (MW=18) from a typical value of 1% to approximately 5%, which decreases the average molecular weight. The two changes approximately cancel each other.

MW Dry air Fractional
Air with
1% water
with 5% water
N2 28.01 78.08% 21.87 77.30% 21.65 78% 21.85 74.10% 20.76
O2 32.00 20.95% 6.70 20.74% 6.64 17% 5.44 16.15% 5.17
Ar 39.95 0.93% 0.37 0.92% 0.37 1% 0.40 0.95% 0.38
CO2 44.01 0.04% 0.02 0.04% 0.02 4% 1.76 3.80% 1.67
H2O 18.01 1.00% 0.18 5.00% 0.90
Total 100.00% 28.97 100.00% 28.86 29.45 100.00% 28.88

Because humans are warm-blooded, human breath is slightly warmer than the surrounding air, and therefore has slightly fewer molecules per unit volume. This is also true of hot air balloons, but they operate at much higher temperatures than human breath and are therefore able to obtain a greater amount of net buoyancy.

comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


Is there any reason why you would have to avert your eyes... i would think that it may create a dust cloud from the keyboard... but it is a fictional situations, so there may be other reasons... 06:02, 16 July 2014 (UTC)

Has anyone noticed Beret's uncanny ability with power cords? Thendenster (talk) 06:29, 16 July 2014 (UTC)

What a stupid unrealistic comic. Things that are blown up with air don't float! >:-C -- 07:26, 16 July 2014 (UTC)

They do if you start off underwater, or start off in your living room, and then dunk the balloon in crazy glue (to give the balloon shell some rigidity), and then take the inflated balloon underwater, or into a caisson, or a hyperbaric chamber - both 'easily' found at underwater worksites.
Or if you're blowing a balloon using a straw that has a one way valve, which goes from your mouth, through your space-suit, and to a balloon which is outside your spacesuit, when you're on the Venusian surface.
They can do so, even on Earth, if the air coming out of your mouth is filtered such that the only bits let through are the components of air that are lighter than the natural mixture of air. (For example, a power line that's been highly charged, could ionise Oxygen atoms much more preferentially than ionising Nitrogen atoms as the flow past the sharp edges of the prongs. The ionised oxygen would react with surrounding bits, and be fixed into a solid state... leaving only the Nitrogen to continue flowing). Nitrogen is lighter than Air. Do this for long enough (a big enough balloon) and it will start floating. If you want to do it faster, and with a smaller balloon - pass the exhaled air over some chemical that absorbs and reacts with carbon-di-oxide (Alkali[ne] hydroxides), absorbs and reacts with water vapour (dessicant), absorbs and reacts with oxygen (bacteria), and absorbs and reacts with nitrogen (nitrogen fixing bacteria). 17:39, 20 July 2014 (UTC)

You obviously don't know how gross a keyboard can be... Also, if you think this is unrealistic, you obviously haven't read enough XKCD. 07:41, 16 July 2014 (UTC)

Yes and as can be seen someone has already added a link to the previous comic on gross keyboards so... Kynde (talk) 07:45, 16 July 2014 (UTC) And who says that it is not blown up with helium or the like. First of all we would never see if a stick character was inflated - so Beret guy could be big and filled with helium. Or it is just his crazy ability that makes his blow into the socket turn the "air" into helium in the PC - or something much lighter since the shown inflation would never be enough to carry a laptop. In the end the whole comic is just an excuse to make three crazy puns (like them or not, that is up to the reader) and refeer back to 237 Kynde (talk) 07:45, 16 July 2014 (UTC)
I think is being sarcastic. Pointing out the fact that things filled with air don't float instead of the obvious impossibility of blowing air through an electric wire. 14:46, 16 July 2014 (UTC)BK
An object filled with air wont go up, but may still bounce out of hand and foat. In this case the sudden increase in volume have ejected the inflated laptop. Since an object almost-as-light-as-air is really sensitive to move of air, the laptop could (in the unlikely case of it happening) behave that way. 09:11, 18 July 2014 (UTC)

Given that Beret Guy often does crazy correctitive things when he perceives something is amiss in his (surreal) visions of the world, I'm wondering if that's a specific protest against having the power chord plugged into the laptop but not the wall (during normal operation, I presume, rather than deliberately depleting the battery of testing the reduced-power settings, or temporarily while other powered devices require the power sockets with more urgency). I don't know whether I personally find this set-up more or less disturbing than a power-chord plugged into the wall but not plugged into the intended laptop. Although (apart from the risk of leaving residue across the pins), the comic's version is at least safer than the opening text of the explanation would suggest. 12:11, 16 July 2014 (UTC)

...inflation in an xkcd comic? Cue the inflatophobes... Greyson (talk) 13:34, 16 July 2014 (UTC)

Beret Guy is obviously exhaling a lighter-than-air gas, either by just taking a large breath of helium beforehand or by a very special cellular breathing process. Moreover, it should be noted that one averts one's eyes before something holy. 11:02, 16 July 2014 (UTC)

You also avert your eyes when you know something is going to be propelled at your head from a compressed air keyboard... -Pennpenn 02:49, 11 June 2015 (UTC)

Transcript accuracy: is Cueball actually looking up in panel 2? He's still typing after all. (Also, [power chords?]) -- 00:48, 17 July 2014 (UTC)

why are all the ips from cloudfare servers? sockpuppets? 09:08, 18 July 2014 (UTC)

explainxkcd is hosted through Cloudflare's cdn and all of us connect through Cloudflare. -- 17:05, 9 July 2020 (UTC)

My mother once blown a lighter than air balloon, our best guess was that it was hot air from some fever or something. 19:56, 18 July 2014 (UTC)

That would only work for as long as the air in the balloon is warmer than the air surrounding it. I doubt that the balloon is that good as an isulator to have this occur for long. --Lupo (talk) 11:13, 16 January 2020 (UTC)

We can see his screen a bit in panel 3. Can anyone tell what he's doing? 22:07, 2 September 2021 (UTC)

Reading xkcd, it looks like. Good catch. Nitpicking (talk) 16:25, 6 December 2021 (UTC)
Looks more like a newsletter(/paper), to me. A traditional printed-style (but PDFed, scanned or HTML+CSSed, obviously) two-column split of various paragraphs and images (no obvious headlines). The obvious image looks less than stick-figure... could be a boxer in action, but the residual resolution (and the method of interpolation needed to 'read between the dots') leaves that a very open issue and maybe flavoured by the eye of this particular beholder, unable to unsee what the vague first imrpession was. But it looks like it was doodled as more than a stick-figure (within the limitations of the pixelation), and doesn't have that basic Comic-like look of XKCD (or even a What-If). Though maybe one of the more Infographic ones, extending well off page? 21:20, 6 December 2021 (UTC)
i did a manual quality upscale. its at https://drive.google.com/file/d/1vznnh7ZkSJXei9brI4sNE9cVM8-QmXOc/view?usp=sharing plushie fan (talk) 00:26, 20 November 2023 (UTC)