# ­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:** 170
**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:** [September 7, 2024, 7:08pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3383 "2024-09-07T19:08:14Z")
> [@digs](#): > > [sigh] But that still doesn’t change the fact that I have four extra ones around my waist… _Four_? For me that would be a rounding error. ☹ ---
**Author:** ![EllisDee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ellisdee/32/4531_2.png) [@EllisDee](https://boards.straightdope.com/u/EllisDee)\ **Post date:** [September 8, 2024, 3:14am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3384 "2024-09-08T03:14:39Z")
> [@Lumpy](#): > > For me that would be a rounding error. Username checks out. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 10, 2024, 5:22am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3385 "2024-09-10T05:22:28Z")
> **[Monocaster](https://xkcd.com/2983/)** > > My competitors say the tiny single tiny caster is unsafe, unstable, and offers no advantages over traditional designs, to which I say: wow, why are you guys so mean? I thought we were friends! ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 10, 2024, 5:32am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3386 "2024-09-10T05:32:22Z")
Seems like a good idea to me. It would only be suitable for fairly smooth surfaces, but be as good as a skateboard. It’ll have less mass than those giant monowheel boards. Of course it needs a self-balancing mechanism to be useful. Even better, instead of a normal wheel, have one of those onmidirectional ones. That way you don’t need any left-right balance. ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [September 10, 2024, 10:04am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3387 "2024-09-10T10:04:20Z")
No Penny Farthing. What a disappointment. ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [September 10, 2024, 10:10am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3388 "2024-09-10T10:10:17Z")
But that would just lead to disagreement on wheel diameter. Which is the determining size for the sake of the graph - the large wheel? The small wheel? An average of both? Note that there was no old-style tractor there, either, despite the fact that tractors have very large rear wheels. ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [September 10, 2024, 10:15am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3389 "2024-09-10T10:15:32Z")
And he has an 18 wheeler at the 16 wheel mark. Ridiculous. I’m taking my mono caster and going home. See you at the hospital! ---
**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:** [September 10, 2024, 3:09pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3390 "2024-09-10T15:09:08Z")
> [@Dr.Strangelove](#): > > Even better, instead of a normal wheel, have one of those onmidirectional ones. That way you don’t need any left-right balance. Just a board with a hemispherical dent and a rigid sphere. Like the old fashioned computer mouses that had an internal ball rolling over the mousepad surface. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 12, 2024, 9:10am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3391 "2024-09-12T09:10:00Z")
> **[Asteroid News](https://xkcd.com/2984/)** > > Their calculations show it will 'pass within the distance of the moon' but that it 'will not hit the moon, so what's the point?' ---
**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:** [September 12, 2024, 3:06pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3392 "2024-09-12T15:06:49Z")
Which raises a very interesting question with probably a very unhappy answer: What _does_ happen when a comet collides with the Moon? I think that might make a pretty good xkcd What-if question. Or a decent SF novel. ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [September 12, 2024, 3:48pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3393 "2024-09-12T15:48:32Z")
Probably not. Comets are too light and lacking in mass to do much against a moon-sized object. Now a wandering asteroid of decent size… ---
**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:** [September 13, 2024, 12:41am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3394 "2024-09-13T00:41:40Z")
There are a couple of different hazards. One is the idea that maybe it smacks hard enough to knock a big hunk off the Moon. So mechanical damage. I agree with you that doesn’t seem too likely. A different hazard is that 100% of the relative kinetic energy of that collision is going somewhere. That might be enough radiant energy to do some damage here on Earth. I just looked at wiki and Halley’s comet masses something around 2E14 kg. WIki also says (edited) > Unlike the overwhelming majority of objects in the Solar System, Halley’s orbit is retrograde. … That retrograde orbit grants Halley one of the highest velocities relative to the Earth of any object in the Solar System. The 1910 passage was at a relative velocity of 70.56 km/s Wolfram Alpha sez that’s ~5E23 Joules of kinetic energy. I would not want to be standing near that energy release. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 13, 2024, 12:57am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3395 "2024-09-13T00:57:55Z")
> [@LSLGuy](#): > > Just a board with a hemispherical dent and a rigid sphere. I’d thought of that but wasn’t sure if it qualified as a “wheel”. The tech is easy; this is from 14 years ago, and advances in batteries, motors, computing, and inertial measurement would make it trivial at a smaller scale these days: [![](https://img.youtube.com/vi/bI06lujiD7E/hqdefault.jpg "A Robot That Balances on a Ball") ](https://www.youtube.com/watch?v=bI06lujiD7E) ---
**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:** [September 13, 2024, 1:08am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3396 "2024-09-13T01:08:38Z")
> [@LSLGuy](#): > > Wolfram Alpha sez that’s ~5E23 Joules of kinetic energy. I would not want to be standing near that energy release. Continuing this musing … The “yield” of the Chicxulub impactor is estimated (wiki again) at ~3E23 J. So Halley hitting the Moon would be an energy release akin to one or maybe two Chicxulubs. The “kiloton of TNT equivalent” used as a convenient unit of measure for nukes is ~4E9 J. So we’re looking at ~1E14 KT of yield. Or ~1E6 Tsar Bombas detonating at their full design power of 100MT. Or ~2E6 Tsar Bombas as actually tested at ~58MT yield. Not an Earth-Shattering Kablooie, but still quite a sight to behold. The Moon masses ~1% of Earth. The more I think about it, 1 or 2 Chicxulubs hitting something 1% as massive as Earth might well spall off some pretty big pieces on the far side from the impact. Plus dig a very impressive crater at the point of impact. And at an impact speed of 7E4 m/s, even a loosy-goosy slushball is going to behave pretty much like a rigid body. ---
**Author:** ![Al128](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/al128/32/16541_2.png) [@Al128](https://boards.straightdope.com/u/Al128)\ **Post date:** [September 13, 2024, 1:42am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3397 "2024-09-13T01:42:44Z")
I’d imagine the amount of moondust kicked up would not be trivial and might impact the earth’s insolation for a year or 6 … that seems to be the most immediate effect ---
**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:** [September 13, 2024, 1:47am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3398 "2024-09-13T01:47:42Z")
Astronomical collisions are typically at speeds that make the material strength of both the impactor and the target irrelevant. A startling fact is that the kinetic energy of an object is equal to its weight in TNT at a relative velocity of only three kilometers per second. ---
**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:** [September 13, 2024, 2:24am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3399 "2024-09-13T02:24:47Z")
Or possibly make some beautiful rings. ---
**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:** [September 13, 2024, 2:32am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3400 "2024-09-13T02:32:33Z")
We’d only get a tiny fraction of that dust, though. ---
**Author:** ![abcdefghij](https://avatars.discourse-cdn.com/v4/letter/a/43a26b/32.png) [@abcdefghij](https://boards.straightdope.com/u/abcdefghij)\ **Post date:** [September 13, 2024, 2:55am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3401 "2024-09-13T02:55:37Z")
> [@LSLGuy](#): > > So Halley hitting the Moon would be an energy release akin to one or maybe two Chicxulubs. Say goodbye to the moon dinosaurs ---
**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:** [September 13, 2024, 4:34am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3402 "2024-09-13T04:34:02Z")
> [@LSLGuy](#): > > What _does_ happen when a comet collides with the Moon? > > I think that might make a pretty good xkcd What-if question. Or a decent SF novel. While not explicit about what does it to the moon, check out **Neal Stephenson** ’s [Seveneves](https://en.wikipedia.org/wiki/Seveneves). The answer is, it’s _not_ good - in a very XKCD way. [Previous page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=169) [Next page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=171)