Everything about Motive Power totally explained
In
thermodynamics,
motive power is an agency, as
water or
steam, used to impart
motion. Generally, motive power is defined as a natural agent, as water, steam, wind,
electricity, etc., used to impart motion to
machinery; a
motor; a mover. The term may also define something, as a
locomotive or a motor, which provides motive power to a system. In current use,
motive power may be thought of as a synonym for either "
work", for example force times distance, or "
power", an effect producing motion, dependending on the context of the discussion.
History
In 1679 physicist
Denis Papin conceived the idea of using steam to power a
piston and cylinder engine, by watching a steam release valve of a bone-digester rhythmically move up and down. In 1698, based on Papin’s designs, mechanical designer
Thomas Savery build the first engine. The first scientific treatise on the energetics of engines was the 1824 paper:
Reflections on the Motive Power of Fire written by French physicist
Sadi Carnot.
As an example, the
Newcomen engine of 1711 was able to replace a team of 500 horses that had “powered” a wheel to pump water out of out a mine, for example to “move” buckets of water vertically out of mine. Hence, we've precursory model to the term
motive power. Based on this model, in 1832, Carnot defined work as “weight lifted through a height”, being the very same definition used to this day.
1824 definition
Carnot states, in the footnotes to his famous 1824 publication, “We use here the expression
motive power to express the useful effect that a motor is capable of producing. This effect can always be likened to the elevation of a weight to a certain height. It has, as we know, as a measure, the product of the weight multiplied by the height to which it's raised.”
In this manner, Carnot is actually referring to "motive power" in the same manner we currently define "
work". If we were to include a unit of time in Carnot's definition, we'd then have the modern-day definition for power:
»
Thus Carnot's definition of
motive power isn't consistent with the modern physics definition of "power", nor the modern usage of the term.
1834 definition
In 1834, the French mining engineer
Emile Clapeyron refers to Carnot’s motive power as “mechanical action”. As an example, during the expansion stroke of a piston engine he states that: “the gas will have developed a quantity of mechanical action during its expansion given by the integral of the product of the pressure times the differential of the volume.” Clapeyron then goes on to use graphical methods to show how this "mechanical action", for example work in modern terms, could be calculated.
Further Information
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