# Why is it that running your finger along the edge of a singular piece of paper results in a paper-cut, while running it alongside a book does not result in many paper-cuts

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Paper cuts ouch

In: Physics

Pressure is inversely proportional to surface area of, in this example, edge of your piece of paper.

More pieces => less pressure = no (or smaller) cut

Book paper is more or less designed to be turned with your fingers, so oftentimes it’s a hint thicker than computer paper to prevent paper cuts specifically.

The concept is similar to lying down on a nail vs. a bed of nails.
If you lie on one nail with all your weight it’s going to puncture your skin, but if you lie on a full bed of nails your weight is spread out a lot more and there isn’t enough pressure for any of the nails to puncture your skin.

If you drag your finger across one piece of paper the pressure is enough for that sharp paper edge to slice through your skin. Add more paper and it becomes harder to cut yourself on it as the pressure of your finger against the paper gets spread out to more papers. Add enough pieces of paper together and you basically have a solid surface that no longer has a sharpness to it