Zeroth Law of Thermodynamics
The law stating that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
Governing formula
If T_A = T_C and T_B = T_C, then T_A = T_B
SI unit
N/A
In depth
The Zeroth Law establishes temperature as a fundamental, universally valid state function and provides the logical foundation for thermometer calibration.
Examples in the real world
A glass thermometer coming to thermal equilibrium with a human body, allowing its scale reading to reflect the body's actual temperature.