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Thursday, August 04, 2005


[Technical warning: This is an esoteric, calculation-filled review of an esoteric book.]

Last week, I quoted from a review of the book Oil Addiction: The World in Peril by Pierre Chomat. Here is a part of the review that I quoted:
One gram of oil gives as much energy as a manual labourer can deliver in a day’s work. He quotes some nice examples: a plane load of tourists, flying from California to see the Great Pyramid of Egypt, consume as much energy as was used in building it. Running a domestic clothes-washer consumes as much energy as it would take a crane to lift the house 23 feet into the air.
I bought the book, and started reading it. It quickly became clear to me that there were serious flaws in Chomat's calculations, particularly the first one, which I'm afraid he used as the basis for making many other mistakes throughout the book. By my calculations, one gram of oil contains approximately 12 watt-hours of energy, something a normal person could easily generate in five or ten minutes of moderate exercise. Chomat did his calculations in calories, and seems to have forgotten that a food calorie (which is also the calorie you see on exercise machine readouts) is equal to 1000 physics-type calories (heat needed to raise 1 ml of water 1 degree C). So most of his calculations seem to be off by a factor of 1000, making oil seem to be a far more potent energy source than it really is (which is still quite potent).

If you're interested in double-checking me, here is what Chomat says:
The thermal energy available in one drop of oil, weighing just one gram, is approximately 10,000 calories, or 10 kilocalories. This is equivalent to the amount of work a laborer can accomplish during a full work day.
In the endnotes, he adds:
The amount of work that a single drop of oil can perform is equivalent to one day of hard physical labor by a human being using a shovel to lift 2 tons of sand (or 4,400 lobs) to a height of 2 meters (or 6.6 feet).

2000 kg x 2 m x 9.81 m/s/s = about 40,000 joules = about 10 kcal
But 40000 joules is only about 11 watt-hours (see Online Conversion). I haven't shoveled sand recently, but I think I could manage a rhythm of one shovel-full every 4 seconds, or 15 per minute. If each load were only 10 kg (22 lbs), it would take me 200 shovels full times 4 seconds = 800 seconds to lift the 2000 kg of sand. That's only 13 minutes! I might not be able to maintain that pace all day long, but it seems reasonable to assume that I could lift a lot more than 2000 kg in a day, and so could most people. We could do much better with a more efficient mechanism than a shovel (pullies, buckets, pedal drive).

What's sad here is that Chomat's error unnecessarily screws up his whole well-intentioned book. He makes up a new term, "ergamine" to describe both the energy in a drop of oil and a human-day of work. He then describes all sorts of energy uses--washing machines, jet plane flights, etc.--in terms of ergamines (for example, claiming it takes 500 ergamines to wash a load of clothes). But since the two are NOT even close to being equivalent, his calculations end up being meaningless. The real situation, that one gallon of gasoline does the equivalent of about three person-days of work, is stunning enough.

I only found one place online that questioned Chomat's calculations (see the comments here). None of the reviewers at Amazon caught the errors.

If you think I'm wrong or otherwise wish to comment on this post, e-mail me: bob AT