Part 2/11:
The essence of the second law can be distilled into a few core ideas: that heat will not flow spontaneously from a colder body to a hotter one, and that mechanical energy eventually dissipates into heat due to factors like friction. The origin of this principle dates back to the early 19th century, primarily driven by advancements in steam engine efficiency. French engineer Sadi Carnot played a pivotal role by formulating how energy transforms from systematic mechanical motion into the chaotic form of heat.
Initially, heat was believed to be a fluid, described as "caloric." However, by the 1860s, scientists began to grasp that systematic energy degrades into random heat—a phenomenon that could not be easily converted back into mechanical energy.