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What is horsepower and why it is a dumb unit to measure power?

Horsepower is a unit for measuring the power output of a specific car and has been used since the beginning of the automotive industry. However, is it still relevant today, and why are there different horsepower ratings for the exact same car in different countries?

The description of power is work over time, or force X distance. And, translated into car terms, it's the amount of force exerted on a car to be able to travel a certain distance. Horsepower is a unit developed by James Watt who specialised in steam engine mechanics which replaced the use of horses. So to translate a common understanding of power by use of horses, he simply asked: "how many horses can my engine replace to get the same workload done?" Thus the horsepower unit became a standard for power outputs.

The confusion comes in when we translate imperial horsepower into metric horsepower. The imperial system's horsepower equation is ft X lb over time (seconds), and then the metric system uses m X kg over time (seconds). So, to do away with the confusion with the same name of horsepower, the metric system uses PS as their output, which stands for Pferdestrke (literally translated means 'horse strength').

The problem with horsepower, however, is its complexity. For example, one horsepower is equal to 550 ft-lb per second. And for the metric system, it equals to 745.6 kg per second cubed. But this is a pain for both engineers and the consumer aborad.

Wouldn't it be so much easier if there was a unit that we could use that will equal to 1kg metre squared per second cubed? Well, it turns out there is and that is the Watt. But that would be a significantly big number for measuring the power outputs, so then we use the Kilowatt instead which equates to 1,000kg metre squared per second cubed! Easy!

Take a look at the video below by YouTube channel, Engineering Explained, on What Is Horsepower And Why It Is A Dumb Unit To Measure Power – America vs Metric.

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