Zeroth Law & Temperature (English)

Описание: The Zeroth Law of Thermodynamics states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. While it may seem like an obvious physical fact, it is considered a fundamental law because it cannot be concluded from the other laws of thermodynamics.
The Basis for Temperature Measurement
The primary value of the Zeroth Law is that it serves as the validity for temperature measurement. By using a third body—such as a thermometer—the law can be restated to signify that two bodies are in thermal equilibrium if they share the same temperature reading, even if they are not in physical contact. This allows us to assign numerical values to "hotness" or "coldness" based on repeatable and predictable changes in material properties, such as the expansion of mercury.
The Naming and Chronology of the Law
The Zeroth Law was first formulated and labeled by R. H. Fowler in 1931. Although its significance as a fundamental principle was recognized more than half a century after the first and second laws were established, it was named the "Zeroth" law because it logically should have preceded the other two. It provides the necessary definition of temperature that the other laws take for granted.
The Zeroth Law in the Context of Other Laws
The Zeroth Law provides the foundation for the four pillars of thermodynamics:
• Zeroth Law: Establishes the concept of temperature and thermal equilibrium, allowing for consistent measurement.
• First Law: Expresses the conservation of energy principle, asserting that energy is a thermodynamic property that cannot be created or destroyed, only transformed.
• Second Law: Asserts that energy has quality as well as quantity, dictated by the fact that processes occur in the direction of decreasing energy quality and increasing disorder (entropy).
• Third Law: States that the entropy of a pure crystalline substance at absolute zero temperature is zero, providing an absolute reference point for determining entropy.
Together, these laws move from defining the state of a system (Zeroth), to accounting for its energy quantity (First), predicting its direction and performance limits (Second), and establishing an absolute scale for its disorder (Third).
Analogy: If the First Law is about the "size of your bank account" (the quantity of energy) and the Second Law is about the "purchasing power" of that money (the quality of energy), the Zeroth Law is the "standard currency" (temperature). Without a standard currency, you cannot accurately measure or compare the value of the energy you are holding or spending.