Pinion

Once, Pinion had lived inside a flour mill, one gear among dozens. A single great water-wheel turned slowly at the river, and that slow turn entered the line of gears and travelled through — small gears spinning it faster, big gears slowing it and forcing it stronger — until at last it reached the millstones and ground the grain. What amazed young Pinion was that the turning was never made anywhere along the line. The river gave one steady push; the gears only passed it hand to hand, trading speed for force and force for speed at each mesh, carrying it around corners, sending it exactly where it was needed. One turn at the water-wheel could become a thousand tiny turns or one enormous grinding one — just by which gears met which, by the ratio of their teeth. That trade — turning handed down a line, reshaped at every step but never lost — became the thing Pinion loved best. When the old mill fell silent, the workshop lifted Pinion out of the dust and gave it a place among the clockwork.

The first day at the workshop, Cog — a gear itself — rolled up beside Pinion, teeth nearly touching. "Show me what you do." Pinion spun twice against the big wheel; the wheel turned once, ponderous and strong. "I trade. Give me a fast easy turning and I'll give you back a slow powerful one — or the other way round, if you mesh me the other way. I flip the direction — two meshed gears always turn opposite ways. I carry motion around a corner. But I never add a scrap of it or lose one; the work in equals the work out. Two small gears in a row, and I turn this way while my neighbour turns that way — motion passed straight along the line." Cog gave a slow, pleased turn, its own teeth meshing for a moment with Pinion's. "A gear teaching gears," it said. "Fitting."

An apprentice named Pip stepped up to a hand-crank linked to Pinion, which meshed with a big gear twice its size, a weight hanging from the big gear's chain. "Count my teeth, then the big gear's," Pinion said. Pip counted — Pinion had half as many. "So I turn twice for each single turn of the big one. That two-to-one is a gear ratio. Now crank." Pip cranked; Pinion whirred around twice, fast and light; the big gear heaved around once, slow — and lifted the weight, which Pip could never have raised by spinning that big wheel with his bare hands. "Two of my turns for one of the big gear's, and in exchange the big gear turns with twice the force. I took your fast, easy cranking and handed back one slow, strong turn. Same work in, different shape out." Pip cranked again, feeling the heavy weight climb. Then Pinion had Pip line up three gears in a row. "Now watch motion travel." Pip turned the first; it spun the second the opposite way; the second spun the third back the first way; and the weight at the end rose. "A bike, a windmill, a hand-mixer — none of them make turning. They pass it along, trading speed for force wherever they need it. Choose your gears, and you choose your trade."