Second Law of Thermodynamics

23.06.2015 |

Episode #8 of the course “Equations that changed the world”

In the scientific field of physics, the study of thermodynamics studies heat and how heat energy can be used to do work. To understand how heat behaves, physicists study it within a “system”—a set of observable parameters. A physicist might study the whole universe as a system, or a single machine could be an observable system.

Experiments in thermodynamics produced repeated behaviors for heat. Physicists codified these general rules of behavior into “laws.” Sadi Carnot is credited as founding the idea of the second law of thermodynamics in 1824. He described how, in a closed system, heat will always warm colder areas, but cold never cools warmer areas without some other event occurring.

Scientists and engineers used this idea to make heat do work as it was transferred from one part of a system to another. However, they found they could not capture all the heat to employ it. For example, when using steam to power an engine, there was no easy way to capture 100% of the power from the steam and transfer it to the engine.

The second law of thermodynamics was expanded in 1926 with the concept of “entropy,” which is effectively the energy that cannot be applied to do work. It is often thought of as “disorder,” “chaos,” or “irreversible processes.” Entropy is irreversible and always increasing, because once the energy slips away from being applied to work, it cannot be recaptured. Therefore, the amount of entropy in the system is continually added to, unless something counteracts it.

By better understanding heat dispersion and entropy, researchers in various fields of physics, chemistry, engineering, and more have been able to more efficiently calculate and understand the processes that affect their systems. The second law of thermodynamics has been called one of the few “perfect” laws of science.


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