The zeroth law of thermodynamics gives

The zeroth law of thermodynamics establishes the concept of thermal equilibrium and lays the foundation for defining temperature. It states that if two systems are each in thermal equilibrium with a third system, they are also in thermal equilibrium with each other. This law ensures that temperature can serve as a fundamental and measurable property for determining thermal equilibrium.

In simpler terms, the zeroth law of thermodynamics implies that temperature is the parameter that determines whether two systems are in thermal equilibrium. This law is crucial because it allows us to compare temperatures of different systems and forms the basis of thermometry.

Additionally, the zeroth law of thermodynamics is essential for understanding the relationship between heat and temperature. It clarifies that heat is a form of energy that flows between systems due to a temperature difference, but systems at the same temperature (thermal equilibrium) do not exchange heat.

In conclusion, the zeroth law of thermodynamics provides a clear explanation of thermal equilibrium and the role of temperature as a defining property, thereby forming a cornerstone of classical thermodynamics.