Heat and Thermodynamics - Introduction
In early days, according to caloric theory of heat, heat was regarded as an invisible and weightless fluid called ?caloric?. The two bodies at different temperatures placed in contact attain thermal equilibrium by the exchange of caloric. The caloric flows from the hot body to the cold body, till their temperature becomes equal. However, this theory failed to explain the production of heat due to friction in the experiments conducted by Court Rumford. Rubbing our hands against each other produces heat. Joule?s paddle wheel experiment led to the production of heat by friction. These observations led to the dynamic theory of heat, according to which heat is a form of energy called thermal energy.
Every body is made up of molecules. Depending on its nature and temperature, the molecules may possess translatory motion, vibratory motion and rotatory motion about its axis. Each type of motion provides some kinetic energy to the molecules. Heat possessed by a body is the total thermal energy of the body, which is the sum of kinetic energies of all the individual molecules of the body.
Temperature of a body is the degree of hotness or coldness of the body. Heat flows from a body at high temperature to a body at low temperature when they are in contact with each other. Modern concept of temperature follows from zeroth law of thermodynamics. Temperature is the thermal state of the body, that decides the direction of flow of heat.
Temperature is now regarded as one of the fundamental quantities.