The physics of paper cutting determines the most dangerous types of paper

Either way you look at it, paper cutting is painful.

Magazines, papers and books harbor a devious potential for small self-inflicted agonies. But other types of paper — like thin cardstock or the thicker stuff used for postcards — are less likely to offend. Scientists have now explained the physics behind why certain cards are more prone to shredding fingers.

In experiments with a gelatin replica of human tissue, the researchers found that a thin sheet of paper tended to shrink before it was cut. Thick paper usually penetrated the material but did not pierce it: Like a dull knife blade, it did not concentrate the force in a small enough area. About 65 micrometers thick was a paper-cut sweet spot — or sore spot — physicist Kaare Jensen and colleagues report in a paper to appear in Physical review E.

This makes dot matrix printer paper more treacherous, the researchers say. (This paper is rarely used today – fortunately for both pinkies and index fingers). (For those reading Scientific news in print: Sorry!)

The angle of the cut also played a role. Paper pressed straight down on the gelatin was less likely to be cut than paper torn across and down.

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

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