# Horsepower

horsepower is a unit of measurement of power , belonging to the English measurement system with the name horsepower (‘horse power’). Its symbol is HP.

## Summary

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• 1 Origin
• 2 Definition
• 3 Formulation
• 4 Conversion to the international system of units
• 5 News
• 6 Note on terminology
• 8 Sources

## Origin

A horsepower [1] is a unit of measurement invented by James Watt in 1782 . The story tells that Watt worked with pony horses, which were used to raise coal from the mines. Apparently he wanted a way to define the amount of force available in one of these animals. He found that, on average, a pony could do 22,000  pounds of work in one minute. He then increased the number by 50% and coined the horsepower measurement at 33,000 pound- feet of work per minute.

## Definition

This unit of measurement corresponds to a unit of force or work, which in the metric system corresponds to the equivalent of the force needed to lift 75  kg to a meter in height, all this in one second (see image). Under the English measurement system , one horsepower corresponds to 33,000 pound-feet of work per minute. In Spanish language it is also often called steam horse or horse power, because it is a unit of power and not force , this is to avoid the misunderstanding of the name in English ( power means both ‘force’ and ‘power’ , depends on the context).

## Formulation

The power (P) is equal to:

P = work / time = force x distance / time

So:

1 HP = (330 lb) x (100 ft) / 1min = 33000 lb x ft / min

It can also be expressed:

1 HP = 550 lb x ft / s

## Conversion to the international system of units

• 1 horsepower equals 746 W (0.746 kW ).

This means that if you put a horsepower animal on a treadmill, connected to an electric generator, you will get 746 watts continuously.

• To convert watts to horsepower, it must be multiplied by 0.00134.
• To convert kilowatts to horsepower, multiply by 1.34.

## Present

It is an arbitrary measure that has been kept alive through the centuries and is now regularly used in the automotive industry. In addition to treadmills and vibrating platforms, it can also be found on the datasheets of mowers, vacuum cleaners and outboards. The term «horsepower» has been replaced by the term watt (in English, watt ), which is the unit corresponding to the SI (international system of units).

## Terminology Note

This unit belonging to the English Measurement System also known as the Imperial System , is written in lowercase except in the case that it initiates a phrase or a title. However, in the consulted sources, its symbol is written in the following variants: HP, Hp or hp.