New Shape Born From Rubber Bands

sciencehabit (1205606) writes "Physicists playing with rubber bands have discovered a new shape. In an attempt to create a spring that replicates the light-bending properties of cuttlefish ink sacs, a team of researchers suspended two rubber strips of different lengths. Connecting the bottoms of the two strips to a cup of water, the shorter band stretched to the same length as the longer one. After gluing the two stretched strips together, the researchers gradually drained the water from the cup. As the bands retracted and twisted from the reduced strain, the researchers were shocked to see the formation of a hemihelix with multiple rainbow-shaped boundaries called perversions. The team hopes their work inspires nanodevices and molecules that twist and transform from flat strips into predetermined 3D shapes on demand." There are several videos attached to the original paper, and all can be viewed without flash.

The usual story: flawed summary

[jbmartin6]

I don't see anything in the paper claiming to have found "a new shape". It also isn't clear why the word "shocked" is used, other than perhaps the results was unexpected. I guess an excerpt from the paper sums it best:

A recent, simple experiment using elastomer strips reveals that hemihelices with multiple reversals of chirality can also occur, a richness not anticipated by existing analyses. Here, we show through analysis and experiments that the transition from a helical to a hemihelical shape, as well as the number of perversions, depends on the height to width ratio of the strip's cross-section. Our findings provides the basis for the deterministic manufacture of a variety of complex three-dimensional shapes from flat strips.

Re:New?

[gstoddart]

To be fair, the abstract doesn't say anything about a new shape, nor do I see anything in the introduction.

Kinda yes, kinda no:

More generally, we introduce the term hemihelix to describe multiple reversals in chirality connected by perversions.

So, they've come up with a term to describe this.

And, lest anybody think they were unaware of the phone cord thing:

Although perversions can also be introduced manually, for instance, by the simple operation of holding one end of a helical telephone cord fixed and twisting the other in a direction counter to its initial chirality

So, they know that people have seen this. They seem to be the ones introducing the term they've applied to describe it.

A new name to an old shape, but mostly they've figured out how to predict it, and then hopefully how to plan for it to build specific shapes.

Re:Old phone cords?

[guruevi]

You're missing the point of the paper. The paper is not there to show "new shapes" that is the reporter that clearly doesn't understand what's going on saying that.

The paper explains HOW these things happen and HOW specific shapes can be modeled (aka calculated or created on purpose) in function of various forces and aspect ratios. They for example, show how to consistently get such a 'kink' (perversion) like the one in your phone cord on every "turn".