text: Thermal physics is the combined study of thermodynamics, statistical mechanics, and kinetic theory of gases.  This umbrella-subject is typically designed for physics students and functions to provide a general introduction to each of three core heat-related subjects.  Other authors, however, define thermal physics loosely as a summation of only thermodynamics and statistical mechanics.
  Thermal physics can be seen as the study of system with larger number  of atom,  it unites thermodynamics to statistical mechanics.