The four laws of thermodynamics
Channel: Thermodynamics For Everyone
Date: 17/09/2021

This video makes the point that thermodynamics has four laws. 

Those four laws combined in different ways replicate all past and expected future observations of processes that take place in the universe. 

In point of fact, unless you work at very cold temperatures in the laboratory, you most likely will only need to use two laws in your day-to-day quest to understand and predict the thermodynamic processes around you.

Zeroth law: If object A has temperature X, and if object B has the same temperature as that of A, and if object C has the same temperature as object B, then object A and C have the same temperature. This law is so obvious it's actually confusing (video explains it all!), and it was actually historically the last law to be introduced.

First law: Two components: (1) Joules are neither created nor destroyed (i.e., law of conversation of energy) and (2) an object has an internal energy that manifests itself as temperature.

Second law: For two objects in contact, the direction of heat interaction is indicated by which object is warmer than the other. The extent of this natural tendency of direction of change is captured in the mathematics of entropy, for which any possible natural direction (meaning it can occur!) occurs only if the entropy of the universe does not change or increases; it can never be negative.

Third law: As absolute zero is approached, heat capacity becomes vanishingly small faster than 1/T so that the change in entropy goes to zero, implying a limiting value of entropy at absolute zero. Customarily, that limiting value is assigned as zero entropy by convention.