Thermal physics deals with collections of large numbers of particles - typically 10 to the 23rd power or so. Examples include the air in a balloon, the water in a lake, the electrons in a chunk of metal, and the photons given off by the sun. We can't possibly follow every detail of the motions of so many particles. So in thermal physics we assume that these motions are random, and we use the laws of probability to predict how the material as a whole ought to behave.
Alternatively, we can measure the bulk properties of a material, and from these infer something about the particles it is made of.

Table Of Content
 
Part I Fundamentals1
Energy in Thermal Physics
2 The Second Law
3 Interactions and Implications
Part II Thermodynamics
4 Engines and Refrigerators
5 Free Energy and Chemical Thermodynamics
Part III Statistical Mechanics
6 Boltzmann Statistics
7 Quantum Statistics
8 Systems of Interacting
ParticlesEnd Matter