Physics and the Tao of Wood

Ignacio på tømmerhogst

Jeg fikk på sensommeren besøk av Ignacio Mosqueira på hogstfeltet. Ignacio tilbringer vanligvis  sine hverdager som astrofysiker i San Francisco. Her kommer hans betraktinger om vedhogst og fysikk:

Not so long ago Olav, a Norse lumberjack, asked a humble visiting astronomer to use his scientific learning to shed some light on the art of woodcutting. Not wanting to disappoint Olav, who had been so kind to him during his all-too-brief stay in Norway, the astronomer set out to abstract as much knowledge as he could from the theory and practice of woodcutting. First, the astronomer decided to experiment on logs of local extraction, and promptly discovered that his skills with an axe left much to be desired. This failure did not faze the astronomer, but simply led him to attack the problem from a different angle.

The astronomer then set about cutting down the tree of knowledge, hoping to gain nuggets of wisdom from first principles . He was soon encouraged to discover that no less a luminary than Sir Isaac Newton had provided clear guidance as to the penetration depth of a fast moving projectile which happens to encounter an unfortunate target in its path. «For the projectile to come to rest», said Newton, «its momentum must be imparted to the target.» This the astronomer could understand having repeatedly lost control of the hefty axe which only the wood managed to stop. «If that’s the case then the problem is solved!», proclaimed the naive astronomer.

«After all, the momentum of the axe is given by its mass times its speed. Therefore, adjusting for the greater density of iron compared to wood should readily give us an answer for the depth of the cut». But not so fast, he soon realized: «Whatever happened to the energy of the axe? Is it not the Tao of the Cosmos that energy shall not be created nor destroyed but only transformed? And what of the strength of the target? Surely chopping down a tree is never the same as tearing down a rock.» And so the astronomer was forced to dig deeper at the roots of the issue, and soon learned that even when the strength of the target can be ignored, such as in cases when the speed of projectile is faster than the speed of sound, the energy of the impact has a vigorous role to exercise. Besides, the axe could not have been moving faster than the speed of sound or else Olav would never have managed to come out unscathed upon hearing the admonition to –«watch out!» — coming from a misguided, axe-wielding astronomer. Undeterred, the astronomer then dove wholeheartedly onto the subject matter by thinking himself a projectile and dropping in on water, sand, mud, rock and so on, and in each case measuring the depth of the penetration. From this he concluded that the results do indeed depend on the nature of the material in question.«Life was easier when I wasignorant,» mused the enlightened astronomer. «I suppose it is time to go back to chopping wood with all its inextricable fibers and flaws,» he conceded wistfully. But then, Olav already knew all that