This blog post examines the historical significance of how the development of the steam engine and machinery replaced human labor and accelerated the speed and efficiency of civilization.
We live surrounded by more machines than we realize. When asked to think of something considered a machine, most people picture cars or washing machines. In the movie ‘3 Idiots’, the protagonist Rancho, when asked by his professor to define a machine, answers that it is anything that reduces human effort—even a pen nib or a pants zipper is a kind of machine.
Numerous tools and devices we easily overlook in daily life can also be classified as machines. As Rancho noted, not only everyday items like pen nibs or zippers, but even simple devices like handles, pulleys, screws, and electrical switches utilize physical principles to reduce human effort. These small devices combine to form larger machines, enabling us to harness their power and efficiency more effectively. I suspect that what the general public considers machines are objects that operate and move using the power of engines or motors, not human strength. Machines like washing machines and automobiles, powered by engines or motors, seem to fall into this category because they significantly reduce ‘human labor’.
Before the 18th century, humanity relied on the muscular power of humans and animals, making livestock crucial as both a means of transportation and a means of production. Later, natural power sources like waterwheels and windmills were also utilized. The development of the coal-powered steam engine in the 1790s brought about an increase in speed and production volume incomparable to the use of primitive or natural power sources. Steam engines were later replaced by increasingly smaller and more controllable power sources—internal combustion engines and electric motors—tailored to specific applications. These now serve as the primary sources of power in our daily lives.
The aforementioned steam engine and internal combustion engine are representative examples of heat engines. A heat engine is a machine that converts thermal energy—microscopic motion at the molecular level—into kinetic energy, the macroscopic motion of an object. Simply put, it means a machine that generates force and motion by burning fuel to create heat. All heat engines receive thermal energy from a high-temperature heat source and transfer part of it to a working fluid inside the engine. The working fluid, heated by thermal energy and thus elevated in temperature, expands as its pressure rises. This expansion forces the working fluid to push against the mechanical components of the engine, generating force and motion. To keep the engine running, the remaining thermal energy is discarded into the cooler ambient air.
The development of machinery did not merely reduce human labor; it brought about profound changes to human civilization as a whole. During the Industrial Revolution, the introduction of machines like heat engines brought about a dramatic increase in productivity, completely transforming the economy and industrial structure. The modern production processes born from this contributed to humanity rapidly urbanizing and forming large-scale economic systems. This chain reaction of mechanical development laid the foundation for today’s affluent lifestyle and diverse technological innovations.
Today, steam engines are primarily used as heat engines in power plants to generate most of the electricity. The steam engine operates by burning fuel to generate thermal energy, which boils the working fluid (water) to produce high-temperature, high-pressure steam. This steam is then discharged into a turbine. As the steam passes through the turbine blades, it pushes them and loses pressure, creating the force and motion necessary to rotate the turbine shaft. The rotating shaft is wound with coils, and stationary magnets are positioned around it. Electricity is produced through electromagnetic interaction. An electric motor can be considered an agent of the heat engine, as it partially converts work produced by the heat engine on one side into work on the other side.
Unlike steam engines, internal combustion engines burn fuel within the heat engine itself, making them smaller than steam engines, which have a combustion chamber separate from the working fluid, with a few exceptions. Furthermore, while steam engines require preheating to bring water to boiling point at room temperature, internal combustion engines can operate immediately upon ignition of the fuel-mixed working fluid with a spark, eliminating the need for preheating. Their compact size and quick start-up made internal combustion engines highly sought after for transportation. They were also used in aircraft before the development of jet engines.
Thermal engines enabled humanity to consume fossil fuels, concentrated solar energy. Approximately 4 liters of gasoline releases the thermal energy equivalent to about 90 tons of plant matter—the same amount of energy produced by all the roots, stems, and grains from a wheat field spanning roughly 160,000 square meters. This immense energy supply allowed humans to harness faster and more powerful forces. John Smeaton, one of the pioneers of the steam engine, estimated that a human working long hours produces about 100 watts of energy. This means that even mobilizing a million slaves could not transport sugar produced in the West Indies or Brazil to Europe faster than a sailing ship. Even if a million people made candles, they wouldn’t produce enough light to hold night games in the Colosseum. The heat engine sparked the Industrial Revolution, brought population growth and extended lifespans, and remains the foundation keeping human civilization running today.
Since the commercialization of the steam engine in the 19th century, the most crucial topic in heat engine development has been ‘efficiency’. The effort to generate large kinetic energy while consuming minimal fuel continues to this day. Thermodynamics is a discipline established from the experience gained during the development of heat engines, and it provides the standard for the most efficient, ideal heat engine.
In 1834, an engineer named Emile Clapeyron reorganized and published Sadi Carnot’s arguments under the title ‘Force Motrice de la Chaleur’ (The Motive Power of Heat). Carnot proved that an engine repeating a cycle of four ideal processes—isothermal expansion, adiabatic expansion, isothermal contraction, and adiabatic contraction—is the most efficient. Its efficiency is given by: (Temperature units are in absolute temperature.)
Efficiency = 1 – (Temperature of the lower heat source / Temperature of the higher heat source)
Thus, he demonstrated that unless a heat engine operates at -273 degrees Celsius, i.e., absolute zero, its efficiency is always less than 1, proving perpetual motion is impossible. Carnot’s derivation process later became the foundation for establishing entropy and the Second Law of Thermodynamics.
Thus, the principles of thermodynamics and entropy were not merely academic discoveries; they became a crucial turning point in realizing the limitations of heat engines available to humans. This realization led to various attempts to increase the efficiency of heat engines, which expanded into modern internal combustion engines, electric motors, and hybrid technology, forming the basis for diverse research and technological development to this day.
Several reasons explain why actual heat engines consume more fuel than ideal ones to produce the same amount of motion. Key factors include heat escaping through the engine’s container, losses due to friction in the working fluid or moving parts, and interactions between actual gas molecules, unlike those in an ideal gas. Many engineers are striving to reduce this lost energy.
Over the past 200 years, humanity has harnessed thermal energy to power its progress, enjoying a level of development incomparable to previous eras. It is anticipated that we will continue to sustain and advance human civilization for a long time using heat engines that burn fossil fuels. Although alternative energy development is active, the use of fossil fuels is expected to persist. According to the International Energy Agency (IEA), consumption of oil, coal, and natural gas accounted for approximately 81% of total energy consumption in 2006. This proportion is projected to remain stable while consumption volumes increase through 2030. To preserve fossil fuels—concentrated solar energy presumed to be finite—for future generations, research and advancement in thermal engines, the foundation of human civilization, remain essential.
