Why/how does cuing ribbon curl when you run the sharp end of a pair of scissors along it? Would any other tool or material ever have this effect?

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*CURLING RIBBON, sorry. I was delirious when I posted this.

This has probably baffled me *since* I was five. What is this sorcery?!?

In: Physics
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ELI5 answer: If you tighten a ribbon at a sharp angle against a scissor blade, and then loosen the ribbon, the ribbon seems to ‘remember’ the bend that you put in it. By running the edge of the scissors along the ribbon, you’re putting a small bend at every point of the ribbon. All together, this continuous bend turns into a curl.

Slightly less ELI5 answer: The physical reason the ribbon remembers a sharp bend is because of [plastic deformation](https://en.wikipedia.org/wiki/Deformation_%28engineering%29#Plastic_deformation). When a polymer (or any other sufficiently pliable material) undergoes enough stress, the molecules permanently rearrange themselves into their new shape. By pulling the ribbon against a sharp blade, you stretch the molecules on the outside of the ribbon more than the blade-facing side of the ribbon. If stretched hard enough, the molecules on the outside plastically deform and permanently elongate. Since the outside is now longer than the inside, the ribbon maintains the bend even when the scissors are removed.

Hope this helps!

There is a german tv series “sendung mit der maus” where they explain stuff for children but everyone generally knows and likes it. They gave some generally accepted reason for your phenomenon which was to some degree incorrect, but the RWTH aachen contacted them and said they were wrong and invited them over and together they made another episode with SEM microscopy and explained everything and its due to small bumps that form in the polymer of the ribbon which causes the tension for the ribbon to stay in that shape.

Video:
https://m.youtube.com/watch?v=GEyXzm-Y0-I

Its on german unfortunately but if you watch it from 4:00 minutes on you will see SEM images (special form of microsopy) of what happens to your ribbon on the small level 🙂

It works on hair too but I don’t recommend it. I knew people back in the day who used to curl their hair this way

Think about folding a piece of paper and then unfolding it. It keeps the fold a little and the paper bends toward it. Certainly material hold their shape when deformed one of these materials is plastic which curling ribbon is made of. You’re essentially using scissors to make a bunch of tiny bends in the ribbon which it keeps the shape of.