![]() ![]() ![]() In the context of cars, broadly speaking, this means that a car with a lot of horsepower will have a higher top-speed than the same car with less horsepower. In SI units, a Watt is 1 Joule per 1 Second.Īnother difference between horsepower and torque is that horsepower is energy output over time, and torque is instantaneous. The core difference between these two sets of units is that whereas horsepower is a measurement of power - referring to an amount of energy transfer over time- Newton-meters are a measurement of torque - a measurement of rotational force, which has no unit of time. If you live in Europe, the outputs will be listed in Watts and Newton meters. If you live in the United States or Canada, those numbers will be listed with the units of SAE certified Horsepower (which is the same as horsepower, but certified by the SAE) and pound-feet. When purchasing a new car, the crib sheet includes two output numbers with the engine: horsepower and torque. James Watt chose to compare his engine, which was capable of sustaining it's power output for a full day, to a horse's average power output over a day. In a similar vein, the output of an average human over the course of a day is 100 watts, which is where we get the term energy servant from. Watt defined this amount as "the amount of work required from a horse to pull 150 pounds out of a hole that was 220 feet deep". While it is true that the maximum output of a horse is around 15 horsepower, when you average the output of a horse over the course of a work day it ends up being around a horsepower. Although Watt may have "bent the truth" to make his engine more appealing, he was not lying. Suddenly his invention became much more tempting. Instead, he compared it to the amount of work a horse could do in a day, giving it the output of ten horses instead of just one. If he said that his expensive engine had the same short-term output as a horse, people wouldn't buy it, as they already had horses. When Watt made his improvements to the steam engine, he understandably wanted to convince people to buy it. Therefore the term "horsepower" may seem slightly misleading, but Watt did have his reasons for such a name. Representation of what one horsepower is in terms of watts. How to Convert Horsepower (metric) to WattĮxample: convert 15 horsepower (metric) to W:ġ5 horsepower (metric) = 15 × 735.49875 W = 11032.Figure 2. Horsepower (metric) to Watt Conversion Table Horsepower (metric) The watt as a unit of power should not be confused with its energy counterpart, the watt-hour (and all its multiples/submultiples). The absolute watt was adopted as the SI unit of power in 1960.Ĭurrent use: As the SI derived unit of power, the watt in all its multiples and submultiples is used in many applications worldwide from radio transmission to use in the electric power industry. 1 absolute watt is equal to 1.00019 international watts. ![]() These were used until 1948 when the General Conference on Weights and Measures re-defined the watt to absolute units, using only mass, time, and length. In 1908, the "international" definitions were defined, with Siemens' definition being adopted as the international watt. It was first proposed in 1882 by William Siemens who defined it as "the power conveyed by a current of an Ampere through the difference of potential of a Volt." This was the definition used at the time within the existing system of units. History/origin: The watt is named after James Watt, a Scottish inventor. It is defined as 1 joule per second and is used to quantify the rate of energy transfer. Wattĭefinition: A watt (Symbol: W) is the SI (International System of Units) derived unit of power. The term was later expanded to include other types of output power such as the imperial and metric horsepower measurements commonly used today. It is believed that Watt built on this idea and introduced the term horsepower, largely in an effort to market his steam engine. As early as 1702, Thomas Savery referenced horses when describing the output of an engine. Watt was not the first person to compare the output of horses to that of engines. History/origin: The term horsepower was adopted in the late 18 th century by James Watt to compare the output of steam engines with the power of draft horses. In addition, when rating electric motors, one horsepower is equal to 746 watts. Boiler horsepower, albeit a less common measurement than either imperial or metric horsepower, is used for rating steam boilers, and is equivalent to 34.5 pounds of water evaporated per hour at 212 degrees Fahrenheit, or 9809.5 watts. lbf/s), while metric horsepower is approximately 735.5 watts (75 kgf.Mechanical horsepower, also known as imperial horsepower, is defined as approximately 745.7 watts (550 ft Definition: The unit horsepower (symbol: hp) is a unit of measurement of power (the rate at which work is done). ![]()
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