Paper cut physics pinpoints the most hazardous types of paper

Any way you slice it, a paper cut is painful. 

Magazines, letters and books harbor a devious potential for minor self-induced agony. But other types of paper — like thin tissue paper or the thicker stuff used for postcards — are less likely to offend. Scientists have now explained the physics behind why some paper is more prone to shred fingers.

In experiments with a gelatin replica of human tissue, researchers found that a thin sheet of paper tended to buckle before it could cut. Thick paper typically indented the material but didn’t pierce it: Like a dull knife blade, it didn’t concentrate force into a small enough area. A thickness of around 65 micrometers was a paper cut sweet spot — or sore spot — physicist Kaare Jensen and colleagues report in a paper to appear in Physical Review E.

That makes dot matrix printer paper the most treacherous, the researchers say. (That paper is seldom used today — fortunately for pinkies and pointer fingers alike.) Paper from various magazines was a close second in the scientists’ tests. (For those who read Science News in print: Sorry!) 

The angle of slicing also played a role. Paper pressed straight down into the gelatin was less likely to cut than paper that cleaved across and down.

Rather than fighting paper’s tendency to cut, the researchers embraced it. They designed a 3-D printed tool they call the Papermachete, which, when loaded with a strip of printer paper, acts as a single-use knife. The blade can cut into cucumbers, peppers, apple and even chicken. The cutting-edge device could serve as a new type of cutlery with low-cost replacement blades.

Future work will study more realistic, finger-shaped materials, rather than flat sheets of gelatin, says Jensen, of the Technical University of Denmark in Kongens Lyngby. “Ideally you would want some test subjects, but it’s hard to find volunteers.”