Engines, Energy, and Oceans: The Story of Two Great Sciences

The story of thermodynamics and fluid mechanics is closely tied to one invention that changed the world: the steam engine.

In the early 1700s, Thomas Newcomen built a steam engine to pump water out of mines and farmlands. Later, James Watt improved it, making the engine more powerful and efficient. Watt’s design became the driving force of the Industrial Revolution, powering factories, trains, and even ships.

But the steam engine created new problems and questions. Empires at that time relied heavily on ships for trade and military expeditions. Building and running these ships required huge amounts of timber—not only for the ships themselves, but also for fuel. Wood was in short supply, so people needed to understand how energy could be used more wisely. This led to the First Law of Thermodynamics: energy cannot be created or destroyed, only changed from one form to another. With this, engineers could calculate how much work could come from burning wood or coal.

Another challenge came from the ships themselves. Even with strong engines, ships moving through water faced drag, the resistance of the water pushing back. Too much drag could cancel out the engine’s power. To study this, Leonhard Euler created equations describing how fluids move, assuming water had no friction. His theory looked great on paper but failed in reality, because real water is sticky—it has viscosity.

Later, Claude-Louis Navier and George Gabriel Stokes improved the equations by including viscosity. Their work gave us the Navier–Stokes equations, which scientists and engineers still use today to understand how fluids flow.

In short, the steam engine didn’t just give us machines—it pushed scientists to discover how energy works (thermodynamics) and how fluids behave (fluid mechanics). These discoveries shaped modern engineering, from ships and airplanes to power plants and rockets.