explain xkcd - User contributions [en]

Talk:3072: Stargazing 4

2025-04-05T07:44:35Z

172.70.242.247: TDEs

First comic explanation I've done. This is... somewhat harder than what I expected. [[User:MinersHavenM43|MinersHavenM43]] ([[User talk:MinersHavenM43|talk]]) 02:46, 5 April 2025 (UTC)

To be clear, the comic says grains of sand on Earth's *beaches* which presumably excludes deserts and such. I think another joke with that panel might be that Earth has more sand than just the beaches.
[[Special:Contributions/108.162.212.31|108.162.212.31]] 03:21, 5 April 2025 (UTC)

Randal is rarely wrong. Have we seen TDEs (tidal disruption events) for Sag A* or only for other supermassive black holes? --[[Special:Contributions/172.70.242.247|172.70.242.247]] 07:44, 5 April 2025 (UTC)

2810: How to Coil a Cable

2023-08-03T17:17:58Z

172.70.242.247: /* Explanation */

{{comic
| number = 2810
| date = August 2, 2023
| title = How to Coil a Cable
| image = how_to_coil_a_cable_2x.png
| imagesize = 366x713px
| noexpand = true
| titletext = The ideal mix for maximum competitive cable-coiling energy is one A/V tech, one rock climber, one sailor, and one topologist.
}}

==Explanation==
{{incomplete|Created by a CLIMBING MARINE A/V TOPOLOGIST - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

When left unattended, long cables often develop knots and look messy, especially if there are several different cables. The causes of this are not well understood, but may relate to socks disappearing in the wash and to clothes ending up within duvet covers. Cables are often carefully coiled - arranged in a compact series of loops - to take up less space or avoid tangling with other cables, either for storage or when only part of a cable's length is needed to make a connection, only to be later found to have tangled and deformed themselves. Cables often remain curved or uneven after uncoiling.

In this comic, Cueball is struggling with such a problematic cable, and blames flaws in the construction of the cable for causing it (step 1). Well-meaning people then descend upon him, eager to share their obscure knowledge of cable-coiling technique that they claim will avoid these issues (a bit like in [[208: Regular Expressions]]). Long, confusing, and potentially contradictory explanations ensue (step 3), and they eventually coil it themselves (step 4). Cueball is unlikely to be able to reproduce this process himself, and may still find deformations in the cable later; he will likely need to return to step 1 the next time he needs the cable coiled.

The joke is that this approach is presented as a viable solution to the cable-coiling problem, to the point of being presented as a four-step tutorial called "How to coil a cable", while it's just a roundabout way of asking someone else to do it for you. This is reminiscent of {{w|Ward_Cunningham#Law|Cunningham's Law}}, which states that "the best way to get the right answer on the Internet is not to ask a question; it's to post the wrong answer". After all, posting the wrong answer will cause some people to [[Duty Calls|compulsively correct it]].

The obvious way of coiling a cable - taking hold of the cable's trailing end as it leaves the hand, and bringing it back around into the hand in a circle, so it forms a simple helix - causes the cable to twist along its length in the same direction for each turn, and requires the person unravelling it to cope with the twisting.

The title text mentions several diverse specialties that have something to say about cables, lines, and/or knots.

The audio technician's way of coiling a cable involves alternating each obvious helix loop with a backhand loop (backwards helix turn) where the loop curls the same way as the other loops, but its 'helix height' is backwards so the trailing end ends up between the rest of the gathered cable and the previous loop. This causes the twists and antitwists to cancel out, resulting in a cable that does not twist while coiled and uncoiled.

The rock climber’s way of preventing twists and tangles in a rope involves “Flaking” a rope - running it through your hands and piling it loosely - which is used when unwinding a coil in to a pile on the ground. This also affords the climber to quickly detect damage and kinks by feel. The reference to rock climbing appears later in the title text when having a rock climber present is mentioned.

A figure-8 coil is used on some boats: the rope is held in one hand, and wound across the forearm to loop under the elbow, then back across the forearm and through the hand in the same direction each time. This also avoids twists.

In general, though the stiffness and cross-sectional profile does affect the tendency to tangle, a similar cable built for the same purpose is likely to suffer from almost exactly the same tendency to tangle when handled the same. As such, the blame laid upon the brand of cable is generally a spurious excuse for what is more likely just down to handling issues. Some particularly problematic cables, such as those used to connect headphones/earphones to their coxial plugs (which are deliberately thin, flexible and may bicurcate into a "three-ended" Y shape with comparatively large terminating housings on all its ends – all potentially confounding factors), can be sometimes advertised as "tangle-free". Usually this seems to be by using a flat-profile cable, for some reason, and yet almost invariably they ''also'' do actually succumb to tangling anyway, as they are repeatedly used and then being shoved back in a pocket or bag with a more or less cursory attempt at neatly coiling them to save untangling time later.

In the comic, however, Cueball appears to be coiling up something akin to Christmas lights (or another more technical cable with many mid-cable side-tapped connectors) which, most people would know from experience, ''definitely'' adds potential for tangles to form when not carefully enough handled during coiling and uncoiling, as well as if disturbed (e.g. rummaged through, looking for something else in its container) during a period of storage.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:How to Coil a Cable Properly

:Step 1
:[Cueball is standing holding a tangled mess of cable]
:Cueball: I need to buy a different brand of cable! This one always twists into spirals and gets tangled.

:Step 2
:[White Hat and Ponytail enter the panel to come to Cueball’s rescue]
:White Hat: No! That's because of how you're coiling it!

:Step 3
:[White Hat holds and coils the cable while he, Hairy, and Ponytail attempt to explain the method behind the cable coiling]
:Ponytail / White Hat / Hairy: ...over-under method... ...figure-8... ...quarter-turn... ...flaking...

:Step 4
:[White Hat presents the well-coiled cable]
:Neatly coiled!

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Hairy]]

2804: Marshmallow

2023-07-27T17:28:46Z

172.70.242.247: Adjust phrasing about source of heat and link to wikipedia article for Atmospheric entry

{{comic
| number = 2804
| date = July 19, 2023
| title = Marshmallow
| image = marshmallow_2x.png
| imagesize = 670x334px
| noexpand = true
| titletext = The increasing number of graham crackers and chocolate bars in orbit has created a growing risk of Kessler s'mores.
}}

==Explanation==
{{incomplete|Created by a CELESTIAL S'MORE - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
This comic shows the atmospheric re-entry process of a capsule similar to that used in the Apollo moon landing program in the late 1960s and early 1970s. This capsule features a fictional Reentry Marshmallow Toasting Module, with a marshmallow on a deployable stick, which is exposed to airflow during reentry.

During reentry, the capsule would presumably be going at orbital speeds, which for Earth are in excess of 8 km/s. This high velocity leads to air in front of the capsule compressing and heating up as it absorbs its kinetic energy (see {{w|Atmospheric entry}} for more details on ways of heating at work). This has the effect of heating the marshmallow. Additionally, reentry heating effects typically look like flames covering the bottom of the reentering object. This is very similar to a common practice on the Earth's surface of holding a marshmallow on a stick over a static fire on the ground, like a campfire, which also heats the marshmallow, improving its taste.

At the start of the panel, the capsule is approaching atmospheric entry, so any aerodynamic forces would not have begun yet. "All systems nominal" is an aerospace phrase that means all systems (including life support, navigation and stability systems) are performing as expected. However, once the atmospheric effects begin then something goes wrong.

Having a long, thin extension to the airflow will disrupt the aerodynamics, as air starts pushing up against the roasting stick, creating an unbalanced torque that pushes the marshmallow further back into the airflow, rotating the entire capsule. This angular acceleration continues until the aerodynamic design of the rest of the capsule plays a significant factor, rotating the capsule back to its original position, and starting the uncontrollable cycle of oscillations anew. Hence, the astronaut on board reports some oscillations to Houston.

This prompts the unnamed astronaut to tell their colleague, Smith, to put away the marshmallow roaster. This would clean up the aerodynamic profile and stop the oscillation. This is met with resistance that the marshmallow is not cooked yet. This may be expected, as due to the design of the module, it appears as though the marshmallow has been on the outside of the capsule for the entire journey, exposed to the vacuum of space. In this situation, it would have radiated all its heat energy away, reaching temperatures near absolute zero (approximately -273.15 degrees Celsius, the absolute coldest temperature physically achievable). A very brief moment of shock heating from atmospheric effects may not have bought the marshmallow up to a consumable temperature, or even affected the internals of the marshmallow at all. The goal of roasting marshmallows is often to melt the inside of a marshmallow completely, so if this is still frozen, that defeats the entire purpose of the module.

"Houston" is the radio {{w|callsign}} for {{w|Christopher C. Kraft Jr. Mission Control Center|NASA Mission Control}}, located in Houston, Texas. During reentry, the superheated air forms a plasma phase and disrupts radio signals. Hence, it is doubtful that Mission Control would have received this communication from the capsule, and it is very unlikely Mission Control would have received further updates from the capsule until the reentry process was largely finished. This would make the Mission Control operators very concerned over the success of the reentry. But as orbital mechanic and spaceman extraordinaire {{w|Scott Manley}} has discussed the feasibility of [https://www.youtube.com/watch?v=Zwf0RWXx8BY roasting a turkey by dropping it from space] (and Randall has himself addressed the issue of {{what if|28|cooking steaks}}), the astronauts featured in this cartoon are not straying too far from accepted marshmallow roasting techniques and should not be reprimanded by NASA.

The caption for the panel muses that maybe the concept of the module was a mistake, which is a fair assessment given the number of flaws in the design. It would indeed be far better to have ''two'' such units, set upon opposing sides of the module and operated in conjunction, to balance rotational forces. Or even three of them, set 120° apart from each other, perhaps automatically and independently actuated to tune out all ''other'' undesired aerodynamic effects – with the added advantage of simultaneously preparing snacks for all three of the astronauts that typically inhabit an Apollo capsule, not just Smith. However, if there is no way to retrieve the marshmallows without exiting the capsule, they would likely be somewhat salty and waterlogged after the time the capsule splashes down and the astronauts can "enjoy" their cooking.

The title text refers to a popular snack of {{w|S'more|s'mores}}, made by placing a marshmallow roasted over a fire with some chocolate between two {{w|Graham cracker}}s, similar to a sandwich. It also refers to a problem in rocketry, known as {{w|Kessler syndrome}}. Kessler syndrome is a scenario where the density of {{w|Low Earth orbit#Space_debris|space junk in low Earth orbit}} is so high that pieces of space junk crash into each other, breaking apart into smaller pieces. This increases the amount of space junk in orbit, setting off a cascade that could render low earth orbit unusable. These two concepts are combined in a ridiculous way, whereby instead of space junk, it is Graham crackers and chocolate bars that are polluting space. These, combined with the marshmallow from the toasting module, would create celestial s'mores, a novel and frankly wacky concept, as the United States space program does not primarily consist of chocolate and Graham crackers.{{Citation needed}}

==Transcript==
:[A space capsule beginning reentry into Earth's atmosphere is shown. There are four versions of this as it moves deeper and deeper into the atmosphere, but shown in a single panel.]

:[The first version is shown to the left with just a bit air resistance shown with thin dotted lines around and behind it. The capsule looks pretty standard with the broad bottom with the heat shield pointing forwards, and the capsule above it narrowing in a pyramid shape. There are a circular shapes (windows?) and some other lines indicating either doors or access panels. The one special feature is on the left, a stick is held back along the edge of the capsule from a extrusion near the bottom of the capsule. At the top of the stick a white square is located. From inside the capsule one of the unseen astronauts is speaking, possibly with ground control. All speech texts are located in rectangular frames with jagged arrows pointing towards the capsule.]
:Astronaut voice: We're approaching atmospheric entry.
:Astronaut voice: All systems nominal.

:[In the second version air resistance has increased a lot, with many more and thicker lines indicating the air resistance. At this point the arm with the white square turns on its pivot so it is now sticking straight out from the capsule far outside the heat shield below. Two lines indicate the circular movement and the release of the stick makes a loud noise:]
:''Fwip''

:[In the third version air resistance continues to increase, but now also the stick and particular the white square at the end begins to heat up, smoke coming of from the white square. Two small lines on either side of the top of the capsule indicates it is shaking.]

:[In the forth version the air resistance is about the same, but there are now six larger lines at the top of the capsule, two on either side and two above indicating more violent shaking of the capsule. The white square on the stick seems to be burning.]
:Astronaut voice: Houston, we're experiencing some oscillations. Vehicle is becoming difficult to control.
:Astronaut voice: Smith, retract that stupid arm.
:Astronaut Smith's voice: No! It's not ready yet!

:[Caption below the panel:]
:In retrospect, the reentry marshmallow toasting module was a mistake.

{{comic discussion}}

[[Category:Space]]
[[Category:Food]]