THE ORIGINS OF HORSEPOWER

 If you’d like to know more about the origins of the word Horsepower… read on…

British inventor James Watt (1736-1819) – the self-same guy who is perhaps more famous for his pioneering work on the earliest of steam-powered engines, first coined the word horsepower to find a measurement that would ‘rate’ the power output of his engines.

To do this he first tested the ability of several horses to lift coal up a shaft using a rope and pulley arrangement. He discovered that, on average, in a single minute the horses could manage 22 000 foot-pounds of work, ie: raise a 220 lb load by 100 ft – or a 22 lb load by 1 000 ft. Fear not if you aren’t familiar with ‘imperial measurements’ – all will become a little clearer at the end of this short article!*

Anyway, the story goes that just in case some of the horses were not as strong as others, Watt increased that figure by 50% – giving 33 000 ft lbs in a single minute and called the measurement that he had deduced ‘one horsepower’.

In truth, a fit man – such as a coal miner or blacksmith – could more than likely do ‘one horsepower’ of work relatively easily for a minute or two – but this new measurement was calculated to reflect the work horses could do over an extended period of time, without needing a comfort break or stop for a cup of tea!

These days, in the UK anyway, engine power is commonly expressed in terms of ‘bhp’ (brake horsepower). The word brake, incidentally, came into the phrase because the power of engines came to be measured by seeing how much force was required to stop the engine’s flywheel from turning – ie: to ‘brake’ it.

The measurement most seen globally is of course expressed in metric units – 75 kilogram metres per second and is often used interchangeably with horsepower – but is in fact a slightly lower unit of power: one PS is in fact about 98.6% of one horsepower…

*Interestingly, not all horsepower remains the same. One such differing measurement is continental horsepower – abbreviated to PS – which stands for ‘pferdestarke’, the German word for horsepower; while in France the same measurement is often given as CV, which stands for ‘cheval-vapeur’.

There you have it – I did mention all would become a little clearer towards the close of the article!

 By Dave Fall