Heat and temperature 

Zeroth law of thermodynamics

Two bodies are said to be in thermal equilibrium if no transfer of heat takes place when they are placed in contact.We can now state the Zeroth law of thermodynamics as follow:

If two bodies Aand B are in thermal equilibrium and A and C are also in thermal equilibrium then B and C is thermal equilibrium

The zeroth law also allows us to introduce the concept of temperature of measure the hotness or coldness of body