Power Grab: The Tractor Horsepower Race

By Robert N. Pripps
Published on October 8, 2019
article image
courtesy Robert Pripps
Case built 110hp steam engines like this between 1913 and 1925.

In 1781, as the story goes, Scotsman James Watt struggled to convince skeptics to buy his new steam engine as a replacement for their draft horses. To prove his machine’s superiority, he measured the pulling force of a horse walking in circles to turn a mill grindstone. Multiplying its pulling force (approximately 180 pounds) by the distance covered in one minute (a little over 180 feet), Watt came up with a new unit of measure: horsepower.

Perhaps the horse could have pulled harder, or could have been urged to go faster – or Watt could have gotten a bigger horse. Nevertheless, what Watt came up with – 550 foot-pound-seconds – was established as horsepower, a rate of doing work.

Watt’s steam engine, by the way, proved to be the equivalent of 33 horses. With that, he began the trend that would eventually, almost completely, replace the horse with mechanical horsepower. On the farm, where the problem is that all the work needs to be done at once, more horsepower has helped to provide the solution.

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