The 1st Law of Thermodynamics is all about energy and its conservation. In 1850 Rudolf Clausius put it into an equation by conducting an energy balance around the working substance inside a piston.

∆U = Q - W

The change in internal energy of a system (U) is equal to the heat (Q) entering the system minus the work ( W ) done by the system. Mayer’s and Joule’s separate quantification of the mechanical equivalent of heat is what enabled Q and W to be mathematically combined.

Energy – a new hypothesis

Energy is an abstract concept.  You can’t touch it or point to it.  It’s a number.  One can calculate the energies for a wide range of natural phenomena and then add the resulting numbers together in the belief that the sum remains constant no matter what changes occur.  Energy increasing here must equal energy decreasing somewhere else. Work just doesn’t happen on its own. Perpetual motion is impossible.

Energy – a paradigm shift

Energy as a concept is both powerful and complicated.  It represents a paradigm, a way of thinking.  Imagine the challenge scientists had in the mid-1800s in discovering such a concept, especially while they held tightly to other competing but incorrect paradigms such as caloric.  Once they accepted the energy paradigm, everything fell quickly into place.  But until that moment occurred, everything remained confusing and muddled.

The deep faith that for every effect, there must be a cause

Acceptance of this new paradigm required faith.  Mayer and Joule had a deep faith that they were on the right path in defining energy and its conservation.  This faith is what pulled them through.  They didn’t accept the absence of cause in the effects they studied. While many may not have even understood that there was a problem that needed solving, Mayer and Joule did.  In the true spirit of science, they latched onto the discrepancies between data and theory and relentlessly pursued resolution.  Such very tiny discrepancies can open a door into an entirely new universe.  Look at the discrepancy between Newton and Einstein regarding the amount of the bending of star light around the Sun.  A very small discrepancy, a very large meaning.  Look at what Joule tried to do in measuring the temperature rise of water due to agitation by a falling weight.  The calorists didn’t believe that such a rise would even occur.  Joule showed them that it would, by about a half a degree.  A very small discrepancy, a very large meaning.

Explore more about the origins of the 1st Law!

To better appreciate the final steps toward the 1st Law, check out Chapter 22 in my book Block by Block – The Historical and Theoretical Foundations of Thermodynamics. Thank you for listening!

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