From Brain Pickings this week.
“Take a pencil to write with on aeroplanes. Pens leak,” states the first of Margaret Atwood’s 10 rules of writing. “But if the pencil breaks, you can’t sharpen it on the plane, because you can’t take knives with you. Therefore: take two pencils.” But even though the pencil has fueled such diverse feats of creative culture as celebrated artists’ sketchbooks, Marilyn Monroe’s soulful unpublished poems, Lisa Congdon’s stunning portraits, and David Byrne’s diagrams of the human condition, it has only been around for a little over two hundred years.
And some math!
An interesting question is to ask how long a straight line could be drawn with a typical HB pencil before the lead was exhausted. The thickness of graphite left on a sheet of paper by a soft 2B pencil is about 20 nanometers and a carbon atom has a diameter of 0.14 nanometers, so the pencil line is only about 143 atoms thick. The pencil lead is about 1 mm in radius and therefore ? square mm in area. If the length of the pencil is 15 cm, then the volume of graphite to be spread out on a straight line is 150? cubic mm. If we draw a line of thickness 20 nanometers and width 2 mm, then there will be enough lead to continue for a distance L = 150? / 4 X 10-7 mm = 1,178 kilometers.