When two bodies of different temperatures keep in contact, heat tends to spread from one body to the other. This means that one of them increases its temperature and the other decreases. Thermal Equilibrium
However, this situation is not permanent, but reaches a limit point where there is no more heat exchange. This point is precisely the thermal equilibrium.
Temperature leveling and the zero equilibrium law of thermodynamics
In every thermal equilibrium phenomenon there is a leveling off of the temperature. Thus, when you mix hot water with cold water, the end result is warm water, which represents a temperature equilibrium point.
Upon reaching the thermal balance between two bodies, two parallel phenomena occur: Thermal Equilibrium
1) the heat flow disappears;
2) the temperature remains stable, in other words, through thermal contact the heat stops when the bodies reach the same temperature.
These two processes are part of the so-called theory of heat.
If a cup of coffee is left to cool or a cold beverage is heated gradually, in both cases the zero equilibrium law of thermodynamics occurs . This law states that if a body is brought into contact with another that has a different temperature, heat is transferred from the higher-temperature body to the lower-temperature body until both reach the same temperature. Thermal Equilibrium
When there is no heat transfer, it is customary to say that the two bodies have reached their thermal equilibrium point. The law of zero equilibrium allows us to understand temperature not based on the properties of a substance, but rather on the basis of thermodynamics.
Homeostasis and thermal balance
The organisms interact with the environment . An animal’s internal temperature depends on two factors: the outside temperature and how it affects the body temperature. The homeostasis mechanism is responsible for balancing all vital functions and therefore also body temperature at proper levels. Thermal Equilibrium
If an individual finds himself in a situation with a very low ambient temperature , his homeostatic system will have to react in some way: increasing physical activity, seeking the heat of the sun or consuming food. These strategies allow for an adequate thermal balance.
In humans, control of body temperature takes place in the brain , more particularly in the hypothalamus. This part of the brain works like a thermostat that balances the loss of heat from the human body.