What is Temperature?
In a qualitative mode, we can depict the temperature of an object as that which determines the esthesis of heat or coldness felt from contact with it.
It is easy to show that when two objectsof the same stuff are placed together ( physicists say when they are put in thermic contact ) , the object with the higher temperature cools while the ice chest object becomes warmer until a point is reached after which no more alteration occurs, and to our senses, they feel the same. When the thermal alterations have stopped, we say that the two objects ( physicists define them more strictly as systems ) are in thermic equilibrium. We can so specify the temperature of the system by stating that the temperature is that measure which is the same for both systems when they are in thermic equilibrium.
If we experiment farther with more than two systems, we find that many systems can be brought into thermic equilibrium with each other ; thermic equilibrium does non depend on the sort of object used. Put more exactly,
if two systems are individually in thermal
equilibrium with a 3rd, so they must besides be in thermic equilibrium with each other, and they all have the same temperature regardless of the sort of systems they are.
The statement in italics, called the zeroth jurisprudence of thermodynamics may be restated as follows:
If three or more systems are in thermic contact with each other and all in equilibrium together, so any two taken individually are in equilibrium with one another. ( quotation mark from T. J. Quinn ‘s monograph Temperature )
Now one of the three systems could be an instrument calibrated to mensurate the temperature – i.e. a thermometer. When a graduated thermometer is put in thermic contact with a system and reaches thermic equilibrium, we so have a quantitative step of the temperature of the system. For illustration, a mercury-in-glass clinical thermometer is put under the lingua of a patient and allowed to make thermic equilibrium in the patient ‘s mouth – we so see by how much the silvern quicksilver has expanded in the root and read the graduated table of the thermometer to happen the patient ‘s temperature.