Horsepower is one of those terms that is ever-present in car talk, like torque, fuel injectors, and automatic transmission. Unlike those other terms, however, the word horsepower begs a number of unique questions. Why is it called a horsepower? Is one horsepower the equivalent to one horse? How much is a horsepower, anyway? To answer these questions we have to look at not just automotive history, but mechanical history in general.
Horsepower and its Use in Selling Early Engines
Back in the days before modern cars had been developed and steam engines were just coming on the scene, the manufacturers of these steam engines had to find a way to convince folks that these engines were worth the investment. People were used to older sources of labor that revolved (literally and figuratively) around the horse. Anyone who could possibly have use of a steam engine would already be familiar with the amount of labor a horse could produce, and what better way for a company to sell their new product, that to show how much better the new steam engines would be than horses.
To this end, James Watt—manufacturer of steam engines—figured out how often a horse could turn a mill wheel in a minute, including how much force was required to do so, and calculated this out. The number he came up with was 33,000 foot pounds of work in one minute. In simple terms, say there is a bucket with 330 pounds of carburetor parts at the bottom of a 100 foot well. A horse is at the top of the well hitched up to a rope that is put over a flywheel and attached to the bucket. The amount of effort it takes the horse to pull the 330 pound bucket 100 feet to the top of the well in 60 seconds is one horsepower.
One Horse Does’t Necessarily Equal One Horsepower
Part of the way this is calculated relies on the understanding that the horse will be doing the action for a long period of time. One horse’s shift spinning the mill wheel or pulling up that bucket would last several hours, and it would do little good for the owner of the horse to run his beast ragged. Therefore, though the standard amount of horsepower for one horse may equal one, over small periods of time a horse may exceed that amount of force.
When looking at state fair records researchers have seen that over the course of a few seconds of activity that a single horse’s horsepower can be as high as nearly 15—such as when it is engaged in an intense pulling contest—but that amount of output is not sustainable over time. When it comes to humans, the average maximum horsepower a human can reach is about 1.2 (though athletes can produce more), but over long periods of time is sustainable at only around 0.1 hp. This comparison between human and horse horsepower helps to illustrate just how important the consideration of horse vs. machine was for our ancestors in the 1700s.
The Use of “Horsepower” and How it Has Changed Over the Years
James Watt had a winning means of illustrating the power of his steam engines when he began to compare them to the power of a horse. His term was so successful that as technology continued to advance away from the regular use of actual horses, the term horsepower continued to be in common use. It is still commonly used today not only for describing your new Ferrari’s engine, but also in places like turbines, other electric motors, or machinery.
As with many historic means of weights or measurements, the term “horsepower” has taken on a life of its own in different areas, with mechanical, metric, electric, air, boiler and hydraulic types horsepowers measuring differently. While our original (mechanical) horsepower measures in at around 750 watts (a term which happens to be named for our friend John), one unit of boiler horsepower is nearly 10,000 watts.
Horsepower and How We View It Today
Though the term horsepower has been around for centuries, the average person’s understanding of the term has changed significantly over the years. James Watt knew that describing his machines in terms of horsepower was a means of telling his buyers who worked with horses how powerful his machines were. Current car salesmen know that their cars with impressively high amounts of horsepower will go from 0 to 60 in a flash, and can use that to entice their buyers. They may not know how much more heavy machinery their car might lift from a well instead of the average horse, but in the end, that timed lap around the Nürburgring is the more important statistic these days.
