5 ms·

Why can you turn clothing right-side-out?

177 points by niyazpk 16y ago

elptacek 16y ago
This is probably a bad thing to post on a thread about visualizing inverting a surface, but since I've been making my clothes for over 2 decades, I had to check this out. So I took off my trousers and pinned the cuffs together along the circumference (it just so happens that I'm making a new winter coat, so I had pins handy), matching the seams to each other. I grabbed the cuffs and pulled one leg up through the other. The result is that the pinned cuffs sit right at the crotch seam -- there is no way to completely invert the trousers any more than this, and I don't think it would be possible even if the pants had a higher lycra content, as there is no way to get the cuffs THROUGH the crotch to complete the inversion. However, if I grab the pinned cuffs through the waist band and flick the trousers away from me, they turn right side out with a lot less effort than it takes to turn them inside out. Also, all of the cash fell out of my pockets.
- ElbertF 16y ago
  So I took off my trousers... You're on the internet. Why are you wearing pants?
  - elptacek 16y ago
    Because I have kids.
  - ToastOpt 16y ago
    You seem to be lost. Reddit is that way --->
- deleted 16y ago
  [deleted]
- niyazpk 16y ago
  See how to do this on a punctured torus: http://upload.wikimedia.org/wikipedia/commons/b/ba/Inside-out_torus_%28animated%2C_small%29.gif http://upload.wikimedia.org/wikipedia/commons/b/ba/Inside-ou...
  - deleted 16y ago
    [deleted]
- Oatmeat 16y ago
  I was able to do it with my jeans, so I expect it's possible with any trousers. You should note that the inversion is not symmetrical. You are basically pulling one pant leg into the other one. In the end you are left with one pant leg which is inside-out and straight and the other pant leg is inside of the first. The inversion of the parameters is now noticeable. You started with basically a donut with a very wide hole (formed by the pant legs -- I'm ignoring the hole where your waist goes). After the inversion, the pant legs form a donut which is very narrow (just the width of the inside of the pant leg) and is very tall (the height of the pant leg).
  - elptacek 16y ago
    I stared at the animated example for nearly two hours last night. I did get the one leg inside of the other donut, but it didn't /look/ like the animated example, so I disregarded it. Thank you -- "not symmetrical" did not occur to me -- it was bugging me. There's a lot of this same sort of visual thought that goes into designing various garments, but the surface is not a torus.
duck 16y ago
I wish HN would show the sub-domain (math.stackexchange.com) because at first I thought there was a new "fashion" SE and I was starting to feel sick. Glad I clicked through though, very interesting stuff.
- Fargren 16y ago
  What exactly would be wrong with a "fashion" SE? I'd find it quite useful.
  - duck 16y ago
    Nothing at all. I was referring to it being posted on HN along with the ever expanding topics.
    - ebtalley 16y ago
      point in case, I got chided for posting a tex question on se instead of tex.se. Silly but that one irked me, tex looks a lot like code to me. On the other hand I did get prompt replies.
ecuzzillo 16y ago
That this is #1 is heartwarming evidence that HN has not even approached the general vicinity of the proverbial shark, let alone jumped it.
eitally 16y ago
That was an impressive answer from Ryan Budney! ... Then I clicked to his homepage and discovered he is a math professor with interest in knots. I love the internet.
- zackham 16y ago
  I took 3 terms of discrete math from him at the University of Oregon a few years back. He was a great instructor and really smart guy that knows more about knots than I realized could be known at the time.
  - shadowsun7 16y ago
    I'd love to know more about knots. Some links, please?
    - Natsu 16y ago
      You want to look up "knot theory." This should get you started, at least: http://en.wikipedia.org/wiki/Knot_theory http://en.wikipedia.org/wiki/Knot_theory http://www.math.unl.edu/~mbrittenham2/ldt/knots.html http://www.math.unl.edu/~mbrittenham2/ldt/knots.html
caf 16y ago
Any discussion that can include the phrase ...consider that if you had a stretchy pair of toroidal pants with vertical stripes... is alright by me!
shrikant 16y ago
An impressive layman indeed, knowing to post a question to StackExchange under Topology. And I mean that sincerely - that page has some pretty awesome 'layperson'-level (as much as it can get, I suppose) information on topology and manifolds in particular, for a an interested onlooker. Typical classy HN stuff :)
- throw_away 16y ago
  I think that it's just tagged 'topology' by 26 people. The original question-poser may not have known the term.
  - cruise02 16y ago
    If you click on the edited date on Stack Exchange sites you can see the revision history. That one shows that Qiaochu Yuan changed the tag from "geometry" to "topology".
Das_Bruce 16y ago
Once you've got one hole you can just consider it like a sack, all the others are superfluous.
- sz 16y ago
  Not true—in the case of a punctured torus (like the shirt with joined sleeves), it's not like a sack at all! It can still be turned inside-out, but it's a little trickier to visualize. You can imagine the hole stretching until you have a pair of identical rings glued together, then it's easy to see that you can shrink the hole the same way except in the other direction. But there's no way to make it look like a sack with holes.
- yummyfajitas 16y ago
  Not necessarily. For all reasonable articles of clothing, yes, it's true. That's because clothing is designed to enclose an interior which is isomorphic to a sphere [1]. Thus, clothing is simply a sphere with holes. But there are plenty of hypothetical clothes for which this isn't true. Consider a mobius strip - like a sack, there is only one hole, but a mobius strip isn't a sack (and you can't patch it shut). [1] I don't want to think about clothing for which this isn't the case, since it would involve the digestive tract.
  - deleted 16y ago
    [deleted]
  - Retric 16y ago
    A real world example of a diffrent topology is is a dress whose straps intercect with one wrapping around the other so they from an X on someones back.
    - yummyfajitas 16y ago
      It sounds like you are describing a racerback: http://www.zadehome.com/images/product/Racerback_Nightie_2_Main.png http://www.zadehome.com/images/product/Racerback_Nightie_2_M... But I think that falls into the category of "sack with a couple more holes".
taitems 16y ago
Weird, this link continually crashes Firefox 3.6.8 on Windows Server 2008.
- RyanMcGreal 16y ago
  Off-topic: why are you browsing the internet on a server?
  - arethuza 16y ago
    To find Wubi?
    - ritonlajoie 16y ago
      Who is Wubi (is that a meme ?)
      - arethuza 16y ago
        It's a rather neat installer for Ubuntu that installs Linux on top of a working Windows system - allowing you to dual boot. The Windows install remains intact. http://wubi-installer.org/ http://wubi-installer.org/
        ritonlajoie 16y ago
        thanks!
  - taitems 16y ago
    Woops, I missed this reply. I'm a front end developer working on intranet software - we all run server 2008 or win7 so we can build/install/test. Try getting the Adobe Creative Suite to run on any version of Server. That's a bit of fun ;)
larsalan 16y ago
google explains it http://video.google.com/videoplay?docid=-6626464599825291409# http://video.google.com/videoplay?docid=-6626464599825291409...
ritonlajoie 16y ago
I made a small search on youtube to see some videos related to turning a sphere inside out. Please have a look at this gem : http://www.youtube.com/watch?v=R_w4HYXuo9M# http://www.youtube.com/watch?v=R_w4HYXuo9M# Especially the snelpiller's comment

177 points by niyazpk 16y ago

This is probably a bad thing to post on a thread about visualizing inverting a surface, but since I've been making my clothes for over 2 decades, I had to check this out. So I took off my trousers and pinned the cuffs together along the circumference (it just so happens that I'm making a new winter coat, so I had pins handy), matching the seams to each other. I grabbed the cuffs and pulled one leg up through the other. The result is that the pinned cuffs sit right at the crotch seam -- there is no way to completely invert the trousers any more than this, and I don't think it would be possible even if the pants had a higher lycra content, as there is no way to get the cuffs THROUGH the crotch to complete the inversion. However, if I grab the pinned cuffs through the waist band and flick the trousers away from me, they turn right side out with a lot less effort than it takes to turn them inside out. Also, all of the cash fell out of my pockets.

ElbertF 16y ago
So I took off my trousers... You're on the internet. Why are you wearing pants?
- elptacek 16y ago
  Because I have kids.
- ToastOpt 16y ago
  You seem to be lost. Reddit is that way --->
deleted 16y ago
[deleted]
niyazpk 16y ago
See how to do this on a punctured torus: http://upload.wikimedia.org/wikipedia/commons/b/ba/Inside-out_torus_%28animated%2C_small%29.gif http://upload.wikimedia.org/wikipedia/commons/b/ba/Inside-ou...
- deleted 16y ago
  [deleted]
Oatmeat 16y ago
I was able to do it with my jeans, so I expect it's possible with any trousers. You should note that the inversion is not symmetrical. You are basically pulling one pant leg into the other one. In the end you are left with one pant leg which is inside-out and straight and the other pant leg is inside of the first. The inversion of the parameters is now noticeable. You started with basically a donut with a very wide hole (formed by the pant legs -- I'm ignoring the hole where your waist goes). After the inversion, the pant legs form a donut which is very narrow (just the width of the inside of the pant leg) and is very tall (the height of the pant leg).
- elptacek 16y ago
  I stared at the animated example for nearly two hours last night. I did get the one leg inside of the other donut, but it didn't /look/ like the animated example, so I disregarded it. Thank you -- "not symmetrical" did not occur to me -- it was bugging me. There's a lot of this same sort of visual thought that goes into designing various garments, but the surface is not a torus.

duck 16y ago

I wish HN would show the sub-domain (math.stackexchange.com) because at first I thought there was a new "fashion" SE and I was starting to feel sick. Glad I clicked through though, very interesting stuff.

Fargren 16y ago
What exactly would be wrong with a "fashion" SE? I'd find it quite useful.
- duck 16y ago
  Nothing at all. I was referring to it being posted on HN along with the ever expanding topics.
  - ebtalley 16y ago
    point in case, I got chided for posting a tex question on se instead of tex.se. Silly but that one irked me, tex looks a lot like code to me. On the other hand I did get prompt replies.

ecuzzillo 16y ago

That this is #1 is heartwarming evidence that HN has not even approached the general vicinity of the proverbial shark, let alone jumped it.

eitally 16y ago

That was an impressive answer from Ryan Budney! ... Then I clicked to his homepage and discovered he is a math professor with interest in knots. I love the internet.

zackham 16y ago
I took 3 terms of discrete math from him at the University of Oregon a few years back. He was a great instructor and really smart guy that knows more about knots than I realized could be known at the time.
- shadowsun7 16y ago
  I'd love to know more about knots. Some links, please?
  - Natsu 16y ago
    You want to look up "knot theory." This should get you started, at least: http://en.wikipedia.org/wiki/Knot_theory http://en.wikipedia.org/wiki/Knot_theory http://www.math.unl.edu/~mbrittenham2/ldt/knots.html http://www.math.unl.edu/~mbrittenham2/ldt/knots.html

caf 16y ago

Any discussion that can include the phrase ...consider that if you had a stretchy pair of toroidal pants with vertical stripes... is alright by me!

shrikant 16y ago

An impressive layman indeed, knowing to post a question to StackExchange under Topology. And I mean that sincerely - that page has some pretty awesome 'layperson'-level (as much as it can get, I suppose) information on topology and manifolds in particular, for a an interested onlooker. Typical classy HN stuff :)

throw_away 16y ago
I think that it's just tagged 'topology' by 26 people. The original question-poser may not have known the term.
- cruise02 16y ago
  If you click on the edited date on Stack Exchange sites you can see the revision history. That one shows that Qiaochu Yuan changed the tag from "geometry" to "topology".

Das_Bruce 16y ago

Once you've got one hole you can just consider it like a sack, all the others are superfluous.

sz 16y ago
Not true—in the case of a punctured torus (like the shirt with joined sleeves), it's not like a sack at all! It can still be turned inside-out, but it's a little trickier to visualize. You can imagine the hole stretching until you have a pair of identical rings glued together, then it's easy to see that you can shrink the hole the same way except in the other direction. But there's no way to make it look like a sack with holes.
yummyfajitas 16y ago
Not necessarily. For all reasonable articles of clothing, yes, it's true. That's because clothing is designed to enclose an interior which is isomorphic to a sphere [1]. Thus, clothing is simply a sphere with holes. But there are plenty of hypothetical clothes for which this isn't true. Consider a mobius strip - like a sack, there is only one hole, but a mobius strip isn't a sack (and you can't patch it shut). [1] I don't want to think about clothing for which this isn't the case, since it would involve the digestive tract.
- deleted 16y ago
  [deleted]
- Retric 16y ago
  A real world example of a diffrent topology is is a dress whose straps intercect with one wrapping around the other so they from an X on someones back.
  - yummyfajitas 16y ago
    It sounds like you are describing a racerback: http://www.zadehome.com/images/product/Racerback_Nightie_2_Main.png http://www.zadehome.com/images/product/Racerback_Nightie_2_M... But I think that falls into the category of "sack with a couple more holes".

taitems 16y ago

Weird, this link continually crashes Firefox 3.6.8 on Windows Server 2008.

RyanMcGreal 16y ago
Off-topic: why are you browsing the internet on a server?
- arethuza 16y ago
  To find Wubi?
  - ritonlajoie 16y ago
    Who is Wubi (is that a meme ?)
    - arethuza 16y ago
      It's a rather neat installer for Ubuntu that installs Linux on top of a working Windows system - allowing you to dual boot. The Windows install remains intact. http://wubi-installer.org/ http://wubi-installer.org/
      - ritonlajoie 16y ago
        thanks!
- taitems 16y ago
  Woops, I missed this reply. I'm a front end developer working on intranet software - we all run server 2008 or win7 so we can build/install/test. Try getting the Adobe Creative Suite to run on any version of Server. That's a bit of fun ;)

larsalan 16y ago

google explains it http://video.google.com/videoplay?docid=-6626464599825291409# http://video.google.com/videoplay?docid=-6626464599825291409...

ritonlajoie 16y ago

I made a small search on youtube to see some videos related to turning a sphere inside out. Please have a look at this gem : http://www.youtube.com/watch?v=R_w4HYXuo9M# http://www.youtube.com/watch?v=R_w4HYXuo9M# Especially the snelpiller's comment