this blog is girtby.net

Slinky Topology

Here is a picture of a slinky that has been turned inside out, or reversed, or … something.

You can see that the circular logo of Questacon is still present, but each of the segments has been reversed.

Frankly, I’m at a bit of a loss to explain it. Well, I can imagine stretching the diameter of the first ring so that it can slide over the outside of the body of the slinky, and then repeating the process so that the entire slinky is turned back on itself. But that would be extremely difficult, and anyway that’s not what I did!

What happened was the slinky mysteriously got itself into a tangle (a 6-year-old may or may not have been involved). I tried to untangle it, fruitlessly, and then noticed that the slinky had been turned inside out in the process. I then cut off the tangled part — which is why the picture contains only part of a logo — and took the photo.

Anyone else care to have a shot at explaining it?

It doesn’t seem so dramatic to me, although I admit I haven’t tried this on an actual slinky.

(1) Have an adult hold the slinky horizontally, pointing at a six-year old boy.

(2) Have a 6-year old put his small hand through the slinky and grab the far-end (i.e. nearest the adult).

(3) [Optionally, for easier handling.] Have the adult twist the far end of the slinky slightly to the right, to widen it. Have the child twist the far end of the slinky to the right, to narrow it. [These identical instructions giving different results makes sense because they are looking in opposite directions.]

[4] Threaten, or otherwise coax, the 6-year old to drag the tip of the slinky through the middle of the body.

[5] Keep threatening, so the 6-year old keeps backing away.

Voila! A slinky that has reversed in orientation, just as you described.

See also: Reversing direction of a curly telephone cord, which uses a different technique.

I think you’ve described the same process as I imagined above, except you’re going through the middle of the slinky and I imagined going around the outside.

The only trouble is that I didn’t go through the middle either. And the 6 year old wasn’t involved at all except as the recipient of some comments about the length of time between the acquisition of the slinky and it becoming tangled.

Now that I’ve thought about it some more (note to self: think THEN blog), I think what I did was open the slinky like a book, pulling out a ring and in the process twisting it over. From there I think it’s possible to wind the twist all the way to the other end of the slinky and create the desired effect.

It’s still hard to wrap my head around though; I’d need to actually try it. Next time we get a tangle I will.