If you’re old enough, you may remember the TV show “Mr. Ed”. Mr. Ed was an amazing talking horse. Right now, I want to talk horsepower.
Today we have automobiles, planes, trains, boats, and motorcycles to help us get where we need to go. To help us with our work, we have tractors, bulldozers, lawnmowers, cranes, forklifts, and wheel loaders. Prior to electricity, the internal combustion engine, and even steam power, our main source of power to accomplish our transportation and work needs was the horse. It’s easy to see why the horse power has been used as a standard to compare the power of different machines.
There are other methods of comparing power output. But, once a standard is set and widely used, it is difficult to change the entire system. (Some may remember when the US tried to change to the metric system.)
Not all horses are equal, so what exactly is a horsepower? First, what is power? Power is a result of the amount of work that is done for a given period of time. Because work is force x distance, we get an equation:
Power = (Force x Distance)/Time
The original standard horsepower was determined as follows:
One horse can turn a 24ft diameter mill wheel 144 times/hour with a pulling force of 180 lbs. Calculated out this comes out to 32,572 ft.lbs per minute. This was then rounded to 33,000 ft.lbs per minute.
There are many different calculations for horsepower. Mechanically, horsepower is a function of torque and speed. To calculate horsepower, multiply torque (in/lbs) by speed (RPM) and then divide by the constant 63,025.
HP = (Torque x RPM) / 63,025
Torque and speed can be altered without sacrificing horsepower through devices like a transmission or gear reducer to either increase torque and decrease speed, or decrease torque and increase speed.
While there are simpler ways to calculate power, and they are more convenient. The horsepower has been an important reference of power ever since our ancestors started comparing the work output of horses and steam engines.
Of course, Mr. Ed may have a different take on all this.