Power is physical work carried out in a certain amount of time. In the below formilae it is given in Nm/s. This is exactly the unit for one Watt, named after James Watt, who made the steam-engine suitable for industrial use. 736 Watts are equal to 1 hp, the old unit of horsepower, which was also invented by him. An interesting fact is that nowadays, for a short period, a horse can produce quite a bit more than 2 hp. In 1765 however, James Watt probably meant the continuous performance of mine-horses for a period of up to more than 10 hours.