# ­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:** 55
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 9, 2021, 2:51pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1082 "2021-11-09T14:51:45Z")
> **[Flinch](https://xkcd.com/2539/)** > > Premed: "Does this count for a physics credit? Can we shorten the string so I can get it done faster? And can we do one where it hits me in the face? I gotta do a thing for first aid training right after." Software engineer: What happens if there’s an interrupt/exception at the same time it’s supposed swing away from my face? ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [November 9, 2021, 2:54pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1083 "2021-11-09T14:54:23Z")
My physics teacher did this demo in high school - and claimed that one year he had to push a student out of the way (the student had not released the ball - he had **shoved** it) ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [November 9, 2021, 2:57pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1084 "2021-11-09T14:57:42Z")
I’m in the engineer camp there, but my initial thought is that it isn’t easy to hang it up in a way that adds the necessary energy to have it hurt me on the way back. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [November 9, 2021, 3:06pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1085 "2021-11-09T15:06:10Z")
If it wasn’t hung up correctly, and the top is allowed to slide back and forth in the direction of travel, then I think it could end up coming back further than expected. Or if it is in a situation where it could come off of its mounting on the ceiling, it wouldn’t hit you in the face, but in the torso or lower. ---
**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:** [November 9, 2021, 3:18pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1086 "2021-11-09T15:18:49Z")
And, strictly speaking, we don’t really know how strong the support chain or other parts of the gadget are, nor how brittle they are… ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [November 9, 2021, 4:36pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1087 "2021-11-09T16:36:09Z")
Hmmm, if the ball’s weight is not evenly distributed (and bowling balls weights are specifically _not_ evenly distributed), then if it rotates while it spins, it may be able to hit you in the face, I think. If the heavier side is towards you on the downswing, but the lighter side is towards you on the return upswing, then it wouldn’t require any violation of conservation of energy to smack you. ---
**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:** [November 11, 2021, 12:24am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1088 "2021-11-11T00:24:58Z")
So, is that second panel Darwin’s Flinch? ---
**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\ **Post date:** [November 11, 2021, 3:45pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1089 "2021-11-11T15:45:39Z")
> **[TTSLTSWBD](https://xkcd.com/2540/)** > > Tomorrow's sessions will be entirely devoted to sewing machine rotary hooks. I would go to this conference in a heartbeat. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [November 11, 2021, 3:56pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1090 "2021-11-11T15:56:34Z")
> [@TroutMan](#): > > Tomorrow’s sessions will be entirely devoted to sewing machine rotary hooks. I’ve actually done quite a bit of sewing in my life, using old school sewing machines. And I have no idea how those things work, they are like magic to me. (Of course, last time I really thought about it was pre-youtube, might go down that rabbit hole at some point.) ---
**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\ **Post date:** [November 11, 2021, 5:12pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1091 "2021-11-11T17:12:35Z")
> [@k9bfriender](#): > > I’ve actually done quite a bit of sewing in my life, using old school sewing machines. > > And I have no idea how those things work, they are like magic to me. I watched a video animation explaining how they work, and it didn’t really help. It still seems like an M.C. Escher drawing, where things magically pass through something else. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [November 11, 2021, 8:38pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1092 "2021-11-11T20:38:37Z")
> [@k9bfriender](#): > > And I have no idea how those things work, they are like magic to me. > > (Of course, last time I really thought about it was pre-youtube, might go down that rabbit hole at some point.) Posting this because I love the animation and the fact that my brain doesn’t let me remember this understanding very long after having examined and understood it. [![](https://external-content.duckduckgo.com/iu/?u=http%3A%2F%2F3.bp.blogspot.com%2F-kLcun4OiBcc%2FUADfAaPM0lI%2FAAAAAAAAAz8%2FDNGyV-TQsHE%2Fs1600%2Fsewing.machine.gif&f=1&nofb=1) ](https://external-content.duckduckgo.com/iu/?u=http%3A%2F%2F3.bp.blogspot.com%2F-kLcun4OiBcc%2FUADfAaPM0lI%2FAAAAAAAAAz8%2FDNGyV-TQsHE%2Fs1600%2Fsewing.machine.gif&f=1&nofb=1) ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [November 11, 2021, 10:24pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1093 "2021-11-11T22:24:57Z")
Nice. ---
**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:** [November 11, 2021, 11:45pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1094 "2021-11-11T23:45:17Z")
My mom is a master of every textile art known to man (or woman), but I can jam a sewing machine just by looking at it. I think it’s because I don’t understand how they work, and if I don’t understand how a thing works, I can’t make it work. I mean, I can maybe see a sewing machine doing something like that crochet-stitch seal at the top of feed bags, where if you pull on the correct end of the string the whole line of stitching unravels and opens. But most stitches don’t work like that. @naita’s GIF there doesn’t really help, either, because that bit that looks like a snake chasing its tail clearly isn’t actually attached to anything. ---
**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:** [November 11, 2021, 11:52pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1095 "2021-11-11T23:52:57Z")
The rotating snake is attached to the machine, but the bobbin at the center is not. The top part of a sewing machine is easy to understand; the needle pushes through the fabric to make little loops at the bottom. The mystery is this: how do you pass thread through those little loops without passing the entire bobbin through each one? And the answer is: you can’t. The whole point to the mechanism is to wrap the loop around the bobbin, which is just floating there. The snake thing just pulls the loop around, and then the loop gets cinched tight by tugging the thread from the top. ---
**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:** [November 11, 2021, 11:54pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1096 "2021-11-11T23:54:37Z")
> [@Dr.Strangelove](#): > > The top part of a sewing machine is easy to understand; the needle pushes through the fabric to make little loops at the bottom. The mystery is this: how do you pass thread through those little loops without passing the entire bobbin through each one? And the answer is: you can’t. The who point to the mechanism is to wrap the loop around the bobbin, which is just floating there. The snake thing just pulls the loop around, and then the loop gets cinched tight by tugging the thread from the top. Exactly—witchcraft. ---
**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:** [November 12, 2021, 12:00am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1097 "2021-11-12T00:00:36Z")
That… might actually have helped. I think. Maybe. Thanks! Though I still don’t see how the rotary hook could be connected to anything, since every spot of it has thread passing both over and under it. ---
**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:** [November 12, 2021, 12:12am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1098 "2021-11-12T00:12:29Z")
Yeah, the animation isn’t quite accurate in that regard. Imagine that the needle drops in _front_ of the snake, and that the mouth is rotated 90 degrees (so that the jaws would be hidden). It can still catch the loop, and it still has to pass half the loop behind the bobbin, but the snake itself can then be supported from behind without a tangle. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 12, 2021, 8:36pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1099 "2021-11-12T20:36:39Z")
> **[Occam](https://xkcd.com/2541/)** > > Oh no, Murphy just picked up the razor. Schroedinger’s cat better be on the lookout. Better hide behind Chesterton’s fence. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 16, 2021, 4:03am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1100 "2021-11-16T04:03:58Z")
> **[Daylight Calendar](https://xkcd.com/2542/)** > > Could be worse. In some towns north of here, it's already December, and the 21st will last for nearly a week. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [November 16, 2021, 2:13pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/1101 "2021-11-16T14:13:58Z")
It seems that would really help Santa to get all his presents delivered in one night. [Previous page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=54) [Next page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=56)