By The Metric Maven
My friend Kat once told me this joke:
Einstein, Newton and Pascal decided to play hide and seek. Einstein put his head against a nearby tree and began counting. Newton only traverses a couple of paces, then reaches into his coat and produces a piece of chalk. He draws a perfect one meter square on the pavement, and then steps into it.
Einstein finishes counting, looks up, and immediately sees Newton standing near him. Einstein says with surprise, “Newton, you really suck at hide and seek, I immediately found you.”
Newton replies “No, no, no you haven’t, you found one Newton per square meter!—-you found Pascal!”
Longtime readers may recall that I’m very much against the adoption of unit identifiers which are the names of persons. If memory serves, Isaac Asimov argued that the names of units should provide a clue as to what they might be. I’m very much of the same mind. As you might imagine I have a first order aversion to the “nesting” of units named after famous scientific persons. When I was taking some long forgotten class in engineering mechanics, I recall a number of problems which defined pressure in pascals. I didn’t question the pascal, but it always seemed a bit remote as far as gaining an intuitive understanding of the amount of pressure present.
I had not really thought much about those ancient exercises in engineering until recently. I was visiting my father in my small hometown, and he was working with another person installing a new Japanese printing press. A technician was installing air for the pneumatics, but was familiar with using pounds per square inch (PSI). He asked me “what is the conversion between pascals and PSI?” to which I could only reply that I could not recall it off the top of my head. The conversion is 1 PSI = 6894.757 pascal. The PSI is so removed in magnitude from a pascal, that one would need to deal in Kilopascals to obtain 1 PSI = 6.895 Kilopascals. But at that moment I was at a loss and could only blurt out what I thought was a useless statement: “well, a pascal is a newton per square meter.” The countenance of the technician brightened. It was clear that my statement actually helped him to understand that the metric system was not somehow creating a mysterious and esoteric alternative to force over area, but that a pascal could actually be related to a pound per square inch in terms of a newton per square meter.
What struck me was that SI, in its quixotic rush to further fete scientists who will never be forgotten as long as the scientific endeavor and humanity continues, have obscured meaning. When I was a boy and first heard pounds per square inch, I understood the concept immediately. The Ye Olde English unit expressed itself within its name. If I had a small one inch square of wood, and I stood on it and weighted 100 pounds, it would be 100 pounds per square inch. If the cross-section of the wood became smaller and smaller the pressure in pounds per square inch would increase. When the area is reduced to a small point it can puncture objects with little applied force. The spear, and arrow rely on an understanding of this principle, and they are some of the first technological tools used by humans. Understanding force over an area, allows one to comprehend why women in high heels attempt to avoid walking on grass, and when they do, they ramble across it on their toes. The pounds per square inch of their heels will easily puncture the sod and form a vacuum that might capture their shoes in place. When neighborhood boys taught me how to patch the inner tubes of my bicycle tires, there was no confusion when they told me how many pounds per square inch were needed for proper inflation. The concept was very intuitive.
The use of the word newton to describe a kilogram-meter per second squared makes as much sense as the pound, and has a name which cannot claim to be a superior nomenclature. The cgs unit of force, the dyne, at least used a word which was not that of a person, and also attempted to use a word which is similar to dynamic. It attempted to describe in words what the unit describes mathematically. In my view SI then doubles down on anthropomorphism at the expense of explanation by calling a newton per square meter a pascal. If a newton per square meter was abbreviated as NSM for newton per square meter, and dual scale gauges found in the US had PSI and KNSM a person who was transitioning to metric could understand that metric was at least on the same planet as the Ye Olde English units. A pascal is an abstract notion by comparison and only serves to conceal information, and not express it.
When I did EMI testing in a GTEM years ago, the amount of noise generated by electrical equipment (often horrible tones) were measured with a device which required the computation of dBspl (decibels Sound Pressure Level) and I recall immediately converting to newtons per square meter for the math used to process the data. The pascal was never really expressive in a way that attracted its direct use. In my view for SI to become more intuitive and useful, questions like this need to be examined, and possible simplifications should be considered, and if they make sense, instituted. If Einstein could not see an obvious relationship between a Newton per square meter and Pascal—why should we?
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