The Zeroth Law of Thermodynamics

The Zeroth Law of Thermodynamics

It is observed that a higher temperature object which is in contact with a lower temperature object will transfer heat to the lower temperature object. The objects will approach the same temperature, and in the absence of loss to other objects, they will then maintain a constant temperature. They are then said to be in thermal equilibrium.  Simply stated the zeroth law states that if objects are touching each other, and if they left alone they will eventually reach the same temperature

Definition provided by Hyperphysics

It is important to mention a few things about the zeroth law.

1. Even though the two objects reach the same temperature they do not have the same thermal energy

2. In order to reach termal equilibrium two things need to happen, first and most important the two objects have time to reach termal equilibrium.  What we experience as "warm and cold" are actually an expression on rate in which objects reach thermal equilibrium. Colder objects have a faster rate of transfer away from your body. It's hotter when energy moves towards you at a fast rate.

Why is it called the zeroth law?  The legend states that when the three laws of thermodynamics (first, second, and third) were proposed, it became clear that these three laws were based on a fundamental "law" which hadn't been published.  The idea of objects reaching a thermal equilibrium if they are left alone, the idea that a thermometer reaches the same temperature of the object it's put in contact with.  So the zeroth law was then offically published with the other laws of thermodynamics and because it is the fundemaental law to the other three, it was placed before the first law, hence the zeroth law

Important Equations

T1 = Temperature of object 1

T2 = Temperature of object 2

T3 = Temperature of object 3