Cite error: There are <ref> tags on this page without content in them (see the help page).When two bodies are in thermal contact and there is no net flow of heat between them, they are said to be in thermal equilibrium. Experimentally, it is found that when two bodies A and B are each in thermal equilibrium with a third body C , then A and B are also in thermal equilibrium with each other . This is called ‘Zeroth Law of Thermodynamics’ ̶ the number ‘zero’ was used because this law logically precedes the ‘first’ & ‘second’ laws of thermodynamics and in fact , is assumed in the two laws.