There are two approaches to the study of thermodynamic. They are known as microscopic approach and macroscopic approach.

Macroscopic view (classical) : I) Fix out attention to certain quantity of matter, substance w/o undergoing into the events occurring at molecular level.
II) the analysis of macro system requires simple mathematical formulae. III) the change in properties can be felt by our senses. IV) In order to describe a system only a few properties are needed. V) examples: P, T

Microscopic view (statistical) : I) Analysis of behaviour of certain matter at molecular level. II) Advanced statistical and mathematical methods are needed to explain the changes in system. III) Properties of individual molecules cannot be sensed. IV) Large no. of variables are needed to describe a system. V) examples: velocity, momentum, impulse, K.E., etc.