DEGREES OF SELF-POWERED MOBILITY
A century ago, the ball-bearing was invented. It reduced the coefficient of friction by a factor of a thousand. By applying a well-calibrated ball-bearing between two Neolithic millstones, a man could now grind in a day what took his ancestors a week. The ball-bearing also made possible the bicycle, allowing the wheel---probably the last of the great Neolithic inventions---finally to become useful for self-powered mobility.
Man, unaided by any tool, gets around quite efficiently. He carries one gram of his weight over a kilometer in ten minutes by expending 0.75 calories. Man on his feet is thermodynamically more efficient than any motorized vehicle and most animals. For his weight, he performs more work in locomotion than rats or oxen, less than horses or sturgeon. At this rate of efficiency man settled the world and made its history. At this rate peasant societies spend less than 5 per cent and nomads less than 8 per cent of their respective social time budgets outside the home or the encampment.
Man on a bicycle can go three or four times faster than the pedestrian, but uses five times less energy in the process. He carries one gram of his weight over a kilometer of flat road at an expense of only 0.15 calories. The bicycle is the perfect transducer to match man's metabolic energy to the impedance of locomotion. Equipped with this tool, man outstrips the efficiency of not only all machines but all other animals as well.
Taken from his 1973 book Energy and Equity
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