1 Watt1 = 1 Joule per second
1 Horsepower2 (hp) = 746 Watts = 2545 BTU's3 per hour
1 Horsepower (hp) = 550 Foot-pounds4 per second
foot-pound: 1-lb force acting through a distance of 1 ft
erg: a 1-dyne5 force through 1 cm
joule: 1-newton6 force through 1 m
1 foot-pound = 1.356 joules
1 erg = 10-7 joules
1 The SI (Systme International) unit of
electrical work is the watt. It represents the generation or use of electrical energy at
the rate of 1 joule per second. The kilowatt is equal to 1000 watts.
2 One horsepower was originally defined as the
amount of power required to lift 33,000 pounds 1 foot in 1 minute, or 550 foot-pounds per
3 One British Thermal Unit (Btu or BTU) was
originally defined as the quantity of heat required to raise the temperature of 1 lb (0.45
kg) of water from 59.5 F (15.3 C) to 60.5 F (15.8 C) at constant pressure of 1
atmosphere. For accuracy, the BTU has now been defined in terms of the joule. One BTU is
equal to 1055 joules. A BTU is equivalent to approximately 0.293 watt-hour.
4 In English system of units, the unit of work
is the foot-pound (ft-lb), which is equal to the amount of work required to raise a mass
of 1 lb through an elevation of 1 ft at sea level and 45 latitude.
5 A dyne is a centimeter-gram-second unit of
force, equal to the force required to impart an acceleration of one centimeter per second
per second to a mass of one gram.
6 A newton is a meter-kilogram-second system,
the unit of force required to accelerate a mass of one kilogram one meter per second per
second, equal to 100,000 dynes.