How was the first law of thermodynamics discovered?

Question

William Audy · Accepted Answer

The first law of thermodynamics is essentially the law of conservation of energy.

It was established after JP Joule discovered the equivalence of heat and work or energy and work.

Thus for a closed system, if a heat #dQ# is supplied from outside, the heat must be used by the system to either perform work or increase it's energy or in the natural case do both of them.

In that case, law if conservation of energy demands that,

#dQ = dU + dW# where symbols carry their usual meaning.

This is the first law of thermodynamics.

Benjamin Asiedu · Answer

undefined The first law of thermodynamics, also known as the law of conservation of energy, was discovered through a series of experiments and observations by several scientists in the 19th century. One of the key contributors was the German physicist Julius Robert von Mayer, who formulated the concept of energy conservation in 1842 based on his studies of the mechanical equivalent of heat. Mayer's work laid the foundation for the understanding that energy cannot be created or destroyed, only transformed from one form to another. Additionally, the experiments conducted by James Joule in the 1840s, particularly his famous paddle-wheel experiment, provided further evidence for the principle of energy conservation. Joule demonstrated that mechanical work could be converted into heat energy, confirming the relationship between mechanical energy and heat. These pioneering investigations culminated in the formulation of the first law of thermodynamics, which states that the total energy of an isolated system remains constant over time, with energy being conserved through various transformations.