How many horses would actually have to trot back and forth under the hood of a small city car if you wanted to propel the engine in a completely natural way? Does a PS actually correspond exactly to the strength of a horse? And is every horse the same strength?
— Image: Shutterstock / Vera Zinkova
Anyone who rides a horse moves with the power of one horsepower – this is the widespread notion when one is asked to visualize the horsepower of an engine. The reality, however, is a bit more complicated and is actually based on a marketing trick from the time when James Watt wanted to sell the steam engine, reports Bayerischer Rundfunk (BR). According to James Watt, if a horse lifts a weight of 150 kilograms 30 meters in one minute, that corresponds to the power of one horsepower. A clever move: the operators of the mines could easily calculate how many horses they could replace with just one steam engine.
Up to 24 HP: Horses have different horsepower
Of course, not every horse can do this feat in the same amount of time. And so horses have very different horsepower. A racehorse, for example, achieves a whopping 15 hp over short distances. A small Shetland pony can hardly keep up. Therefore, how much horsepower a horse can actually produce ultimately depends on whether or not it can surpass the horsepower arbitrarily set by James Watt. According to BR, a single horse can theoretically even achieve up to 24 hp.
