Note: the notes for this article are much longer than the article itself

For the first time in a long time, I took a clean sheet of A4 and drew a straight line down the middle to split it into two columns.*

I started making notes with a pen, and stopped to stare in horror at the tortured traffic accident I had produced. It was ugly. Now I know how dentistry students feel when they make a mess out of their orthodontics practicals.

I stopped writing on paper when I graduated 3 years ago. I switched from using pen to pencil after finishing secondary school 8 years ago, when I discovered the pencil's greater tolerance to slipshod hand strokes.**

Enough time has been wasted, back to the books.


Notes:
* with no columns, too much paper will be wasted as most lines will be just a few words long. I find wasting clean paper to be such a sin.

** A ball point pen's line darkness is extremely sensitive to applied pressure. One can even say that there is a singularity. If you hover the pen very lightly across the page you might find that there is no ink applied. But increase the pressure a bit and the darkness jumps up markedly.

On the other hand, a pencil's line darkness is almost linearly proportional to the applied pressure. An increase in applied pressure will result in a proportional increase in line darkness.

This phenomenon can be easily explained by looking at the mechanism by which the pen and pencil applies the ink/graphite.

The ball point pen uses a sphere within the tip. When the sphere rolls, it carries ink from within the housing to be applied onto the paper.

The darkness of the pen's line can be controlled by changing the applied pressure (within a small range). This is because a greater pressure will cause the pen's sphere to press into the paper, and thus come in contact with a greater surface of the paper and therefore apply more ink on the paper. This is why smooth and hard surfaces cannot be marked by a ball-point pen: the smooth surface does not provide enough friction to roll the ball, and the hardness means that the surface does not deform and hence the inked ball comes in contact with a very small area on the surface.

In contrast, a pencil applies graphite by shearing the graphite off the graphite shaft. A greater applied pressure will cause more graphite to be sheared off, resulting in a darker line.