Horsepower-hour
Encyclopedia
A Horsepower-hour is an outdated unit of energy
, not used in the SI system of units
. The unit represents an amount of work
a horse is supposed capable of delivering during an hour (a horsepower
integrated over a time interval of an hour). Based on differences in the definition of what constitutes the 'power of a horse', a horsepower-hour differs slightly from the German "Pferdestärkenstunde" (PSh):
The horsepower-hour is still used in the railroad industry when sharing motive power (locomotives.) For example, if railroad A borrows a 2,500 horsepower locomotive from Railroad B and operates it for twelve hours, Railroad A owes a debt of (2,500 * 12) 30,000 horsepower-hours. Railroad A may repay the debt by loaning Railroad B a 3,000 horsepower locomotive for ten hours.
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
, not used in the SI system of units
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...
. The unit represents an amount of work
Work (thermodynamics)
In thermodynamics, work performed by a system is the energy transferred to another system that is measured by the external generalized mechanical constraints on the system. As such, thermodynamic work is a generalization of the concept of mechanical work in mechanics. Thermodynamic work encompasses...
a horse is supposed capable of delivering during an hour (a horsepower
Horsepower
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...
integrated over a time interval of an hour). Based on differences in the definition of what constitutes the 'power of a horse', a horsepower-hour differs slightly from the German "Pferdestärkenstunde" (PSh):
- 1.014 PSh = 1 hph = 1,980,000 lb·ft = 0.7457 kWh.
- 1 PSh = 0.73549875 kWh = 2647.7955 kJJouleThe joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
(exactly by definition)
The horsepower-hour is still used in the railroad industry when sharing motive power (locomotives.) For example, if railroad A borrows a 2,500 horsepower locomotive from Railroad B and operates it for twelve hours, Railroad A owes a debt of (2,500 * 12) 30,000 horsepower-hours. Railroad A may repay the debt by loaning Railroad B a 3,000 horsepower locomotive for ten hours.