ElI5: Why a pen sometimes refuses to write on a specific part of the paper but works perfectly fine everywhere else?

Question

ElI5: Why a pen sometimes refuses to write on a specific part of the paper but works perfectly fine everywhere else?

In: Other

Answer 1

Ballpoint pens operate with a freely-spinning ball at the tip (thus the name). As you drag the tip of the pen across a surface, the friction on the ball causes it to spin, “dipping” it into the inside of the pen (where there is ink) and then transferring it to the paper. Imagine an ink-coated tire leaving marks wherever it rolls.

Microscopically, paper’s surface is rough or kind of “furry” – the plant fibers that make up the paper all stick up and make it a textured surface. This creates the friction that the ballpoint pen needs to roll. If a section of the paper is “flattened,” then it doesn’t create enough friction for the ballpoint pen to roll, and the ball stays stuck without any ink. The tip of the pen still gets dragged over the paper, but it never deposits any ink.