# ­xkcd thread **URL:** \ **Category:** Cafe Society\ **Tags:** comic-strips\ **Created:** [May 28, 2020, 12:57am UTC](https://boards.straightdope.com/t/xkcd-thread/854574 "2020-05-28T00:57:03Z")\ **Posts on this page:** 20\ **Page:** 280
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [February 10, 2026, 9:32pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5583 "2026-02-10T21:32:55Z")
That was fun and informative. Thanks, neighbor – I owe you a tasty slice of Corky’s pizza! ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [February 11, 2026, 12:48am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5584 "2026-02-11T00:48:44Z")
For the GAU-8 and the HSh-6-30 I don’t think they are self-powered so the calculated weight to thrust wouldn’t be accurate. Though a bigger oversight is that the bullets are useless dead weight. You would get more thrust with less weight just by shooting the cartridges with no bullets. In fact really you’d want to take the entire magazine holding the bullets and reconfigure it to just contain powder, with a suitably designed exhaust nozzle. IOW, strip out most of the weight of the gun and turn it into a solid propellant rocket. ---
**Author:** ![Askance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/askance/32/8281_2.png) [@Askance](https://boards.straightdope.com/u/Askance)\ **Post date:** [February 11, 2026, 3:11am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5585 "2026-02-11T03:11:09Z")
Not sure I follow - the thrust is from the mass of matter ejected (x velocity) whether bullets, gas, or cartridge fragments. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [February 11, 2026, 3:16am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5586 "2026-02-11T03:16:44Z")
All of the kinetic energy comes from the propellant. If that propellant is applying the kinetic energy to the bullet or cartridge fragments, then you either gain nothing or else it is actually less efficient. You’d do better to either not carry the dead weight of the bullets to begin with, or even better substitute their weight in propellent for more energy. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [February 11, 2026, 1:39pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5587 "2026-02-11T13:39:34Z")
> [@Lumpy](#): > > For the GAU-8 and the HSh-6-30 I don’t think they are self-powered so the calculated weight to thrust wouldn’t be accurate. True. For the GAU-8 (and M61 Vulcan) the aircraft hydraulic system powers hydromotors that rotate the barrels and operate the ammo drum and cartridge feed mechanisms. The breechblock cycling is a mechanical cam system as part of the rotation of the breech assembly. The round actually firing is triggered electrically from the aircraft electrical system; there is no mechanical firing pin. I can’t speak authoritatively to the HSh-6-30, but I’d expect it’s similar. Whether electrical or hydraulic, there’s a bunch of horsepower being injected into the system from someplace external. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [February 12, 2026, 12:26pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5588 "2026-02-12T12:26:58Z")
> **[Installation](https://xkcd.com/3206/)** [![](https://imgs.xkcd.com/comics/installation.png) ](https://imgs.xkcd.com/comics/installation.png) “Do YOU remember the skylight being this big?” ---
**Author:** ![Ulf\_the\_Unwashed](https://avatars.discourse-cdn.com/v4/letter/u/b4bc9f/32.png) [@Ulf\_the\_Unwashed](https://boards.straightdope.com/u/Ulf_the_Unwashed)\ **Post date:** [February 12, 2026, 2:23pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5589 "2026-02-12T14:23:33Z")
Okay, I really like this one! ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [February 12, 2026, 4:08pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5590 "2026-02-12T16:08:03Z")
I’ve hired contractors like that. The worst was when they laid sod in the walk-out basement. Took months to get the manure smell out of the house. 🤪 ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [February 12, 2026, 4:14pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5591 "2026-02-12T16:14:43Z")
The inside vs outside distinction is so arbitrary. ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [February 12, 2026, 4:17pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5592 "2026-02-12T16:17:42Z")
walk-out basement = walk-in yard ---
**Author:** ![Civil\_Guy](https://avatars.discourse-cdn.com/v4/letter/c/d78d45/32.png) [@Civil\_Guy](https://boards.straightdope.com/u/Civil_Guy)\ **Post date:** [February 12, 2026, 4:17pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5593 "2026-02-12T16:17:52Z")
Thank goodness they weren’t digging their own water well. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [February 12, 2026, 4:30pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5594 "2026-02-12T16:30:35Z")
The hardest part about digging upwards is shoring up the hole so it doesn’t immediately refill with air. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [February 12, 2026, 7:47pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5595 "2026-02-12T19:47:08Z")
My brother threw a “lawn party” in college, where he and his roommates bought sod, and covered the floor of their dorm living room. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [February 14, 2026, 3:49am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5596 "2026-02-14T03:49:27Z")
> **[Bad Map Projection: Zero Declination](https://xkcd.com/3207/)** [![](https://imgs.xkcd.com/comics/bad_map_projection_zero_declination.png) ](https://imgs.xkcd.com/comics/bad_map_projection_zero_declination.png) “‘The zero line in WMM2025 passes through a lot of population centers; I wonder what year the largest share of the population lived in a zone of less than 5° of declination,’ he thought, derailing all other tasks for the rest of the day.” ---
**Author:** ![N9IWP](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/n9iwp/32/3154_2.png) [@N9IWP](https://boards.straightdope.com/u/N9IWP)\ **Post date:** [February 14, 2026, 12:17pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5597 "2026-02-14T12:17:02Z")
The agonic line used to pass through Wisconsin, and is now goes through the MSP metro, which means (assuming it is continuous) it passed through my house. Brian (The lines are updated every 5 years on aeronautical charts) ---
**Author:** ![carlb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carlb/32/5930_2.png) [@carlb](https://boards.straightdope.com/u/carlb)\ **Post date:** [February 14, 2026, 1:57pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5598 "2026-02-14T13:57:43Z")
OK, I’ll admit it. I don’t understand this one at all. I’m usually really good with maps, and inferring the humor in a comic, even when I don’t understand the specifics of the underlying science. But I’ve got nothing here. Can someone help? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 14, 2026, 2:14pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5599 "2026-02-14T14:14:57Z")
All flat map projections include distortions. Many map projections are cylindrical (because that results in a rectangular map, and we like rectangles), and on a cylindrical projection, the distortion is greatest for points near the poles. But the poles are, in some sense, arbitrary points on the Earth’s surface: They’re relevant for rotation, but why should rotation be the basis for how we set up maps? So this projection, instead of using the rotational poles, uses the magnetic poles. Since the magnetic poles are different from the rotational poles, this map is distorted in different ways than a familiar projection. But since the magnetic poles are close to the rotational poles, it doesn’t look too different. ---
**Author:** ![Toxgoddess](https://avatars.discourse-cdn.com/v4/letter/t/f08c70/32.png) [@Toxgoddess](https://boards.straightdope.com/u/Toxgoddess)\ **Post date:** [February 14, 2026, 2:29pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5600 "2026-02-14T14:29:24Z")
I certainly get the “derailed for the rest of the day” outcome. How many times have we all been derailed when an idle thoght suddenly blooms into a short-lived obsession? ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [February 14, 2026, 2:36pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5601 "2026-02-14T14:36:09Z")
So, that’s what i thought the map was. But i guess i don’t get why it’s an especially bad projection. I also didn’t know what WMM2025 is. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 14, 2026, 2:48pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/5602 "2026-02-14T14:48:03Z")
> [@puzzlegal](#): > > I also didn’t know what WMM2025 is. From a quick Google, it’s the current standard model describing the magnetic field of the Earth. The actual total magnetic field is ludicrously complex, since it’s affected by every piece of iron everywhere, on every scale: Move your refrigerator (or your car), and the magnetic field of the Earth changes. We can’t model the field to that level of detail, so we make models that can model it to a more realistic level of detail. [Previous page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=279) [Next page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=281)