The formulation of the conservation law for mechanical energy had its scientific roots in at least three areas of theoretical mechanics: (1) The principle of conservation of mechanical work… (2) The principle of conservation of vis viva… (3) The principle of conservation of (1) and (2) taken conjointly…that in every transfer of potential energy into kinetic energy and vice versa the total energy remains unchanged.  By 1750 this law of conservation of energy had been accepted for ideal mechanical systems – Erwin N. Hiebert [1]

Path to the rudimentary version of the conservation of mechanical energy (1750)

In a previous post (here) I shared about the power of illustrations to convey content. In this post I share one such illustration (right) from my book, made in collaboration with my wonderful illustrator Carly Sanker, that summarizes the historical journey to the conservation of mechanical energy.

But what about heat?

The arrival of the steam engine in the 1700s left scientists wondering. What is it about this heat engine that causes work (mgh) to be done? You see, the gulf between the 1750 conservation law around mechanics and the 1850 conservation law around energy was huge. Scientists knew that some thing must be conserved based on the impossibility of perpetual motion and the equality between cause and effect. They just didn’t know where heat fit into the equation.

From the single body to many particles

Newton’s force-based mechanics worked extremely well for the movement of celestial and terrestrial bodies that we could see, but it was initially useless for the movement of bodies we couldn’t see.  Accounting for such movements became the single most critical next step in the development of energy entering the 19^th century, and the only means of doing such accounting at that time was with a thermometer.  The beauty of the thermometer was that it enabled discovery of energy and its conservation without requiring one to understand the link between its measurement and the movement of those invisible bodies.  That understanding would come later once early physicists began using Newtonian mechanics to model gases as a collection of colliding hard spheres.

Learn more!

Explore more about the path to the conservation of mechanical energy in Chapter 12 of my book, Block by Block – The Historical and Theoretical Foundations of Thermodynamics. You’ll begin to understand the extent of the gulf that existed between 18^th century mechanics and 19^th century thermodynamics.  It was huge.

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[1] Hiebert, Erwin N. 1981. Historical Roots of the Principle of Conservation of Energy. The Development of Science. New York: Arno Press. p. 95.