What is Horsepower

The term horsepower is generally defined as, "the work done at a rate of 550 foot-pounds per second". However, there is no standard definition for the term horsepower. It is the British unit of power, also known as imperial unit. The unit is not in use today, since it was replaced by watt, an SI unit. SI is an abbreviated form of Système International d'Unités. Although the unit is not used today, it was applied to compare the power of steam engines with those of draft horses.

Mechanical Horsepower
The word horsepower was coined by James Watt. The origin of the word horsepower has an interesting little history behind it. Ponies and horses were used for the generation of power before the invention of the engine. James Watt studied the power usage by ponies to lift the material in coal mines. After several experiments and calculations, he found that a pony was able to complete 22,000 foot-pounds of work per minute i.e., the pony lifted 22,000 pounds to a height of one foot in one minute. Going by the estimate that a horse is 50% more powerful than a pony, Mr. Watt arbitrarily estimated the value of a mechanical horse power to be 33,000 foot-pounds per minute. Thereafter, the term horsepower came into popular use. The exact value of the mechanical horsepower calculated by James Watt was 32,400 foot-pounds per minute. However, it was afterward rounded off to the value of 33,000 foot-pounds per minute.

Metric
The term metric horsepower originated in Germany and became popular the world over. The various units that are used to measure mechanical power are, 'PS', 'CV' and 'ch'. The unit, 'PS' is used in South America, Europe and Japan. Metric power amounts to 98.6% of mechanical horsepower. CV is the French equivalent of the German unit PS.

Boiler
The term is used to measure the power of boilers i.e., the work done per unit time. One boiler horsepower is the amount of energy required for the evaporation of 15.65 kg water in a single hour. The evaporation of water in the process to measure the boiler horsepower is done at a temperature of 100^oC. The term, 'boiler horsepower', was first used in 1876.

Electrical
Measurement of power of various electrical devices is done by means of electrical horsepower. The value of an electrical horsepower is 746 Watts.

Difference Between Torque and Horsepower
Torque is defined as the engines' ability to do work. It is not the same as horsepower. On the contrary, it is a component of horsepower. Horsepower, as discussed above, is the rate at which the engine operates.

How to Convert Torque to Horsepower
The formula to convert torque to horsepower is given below.
Horsepower = [[torque/(foot*foot-pounds)]*[rotations per minute/(rotations per minute)]] /5252

Drawbar Horsepower
The power required by a railway locomotive to pull a train equals to a drawbar horsepower. Instead of calculating or deriving the value of drawbar horsepower, it is actually measured. A 'dynamometer car' was used to measure the drawbar horsepower. In the process of measuring the horsepower, the dynamometer car records the pull exerted on the locomotive.

Today, the unit used instead of horsepower is watt. But car enthusiasts and truck owners still use the 'horsepower language'. The origin of the word horsepower and the related facts make it an interesting concept to study. I hope 'what is horsepower' is now no more a question for you.