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hubie writes:

Researchers cut to the chase on the physics of paper cuts:

If you have ever been on the receiving end of a paper cut, you will know how painful they can be.

[...] To find out why paper is so successful at cutting skin, Jensen and fellow DTU colleagues carried out over 50 experiments with a range of paper thicknesses to make incisions into a piece of gelatine at various angles.

Through these experiments and modelling, they discovered that paper cuts are a competition between slicing and "buckling". Thin paper with a thickness of about 30 microns, or 0.03 mm, doesn't cut so well because it buckles – a mechanical instability that happens when a slender object like paper is compressed. Once this occurs, the paper can no longer transfer force to the tissue, so is unable to cut.

Thick paper, with a thickness greater than around 200 microns, is also ineffective at making an incision. This is because it distributes the load over a greater area, resulting in only small indentations.

The team found, however, a paper cut "sweet spot" at around 65 microns and when the incision was made at an angle of about 20 degrees from the surface. This paper thickness just happens to be close to that of the paper used in print magazines, which goes some way to explain why it annoyingly happens so often.

[...] ensen notes that the findings are interesting for two reasons. "First, it's a new case of soft-on-soft interactions where the deformation of two objects intertwines in a non-trivial way," he says. "Traditional metal knives are much stiffer than biological tissues, while paper is still stiffer than skin but around 100 times weaker than steel."

The second is that it is a "great way" to teach students about forces given that the experiments are straightforward to do in the classroom. "Studying the physics of paper cuts has revealed a surprising potential use for paper in the digital age: not as a means of information dissemination and storage, but rather as a tool of destruction," the researchers write.

Journal Reference: Sif Fink Arnbjerg-Nielsen, Matthew D. Biviano, and Kaare H. Jensen, Competition between slicing and buckling underlies the erratic nature of paper cuts, Phys. Rev. E 110, 025003 – Published 23 August 2024 DOI: https://doi.org/10.1103/PhysRevE.110.025003

Original Submission