Macroscopic and Microscopic Approaches

Macroscopic
and Microscopic Approaches


Microscopic approach uses the statistical considerations
and  probability  theory, 
where  we deal with “average” for
all particles under consideration. This is the approach used in the disciplines
known as kinetic theory and statistical mechanics.

In the macroscopic point of view, of classical
thermodynamics, one is concerned with the time-averaged influence of many
molecules that can be perceived by the senses and measured by the instruments.

The pressure exerted by a gas is an example of
this.  It results from the  change 
in momentum of the molecules, as they collide with the wall. Here we are
not concerned with the actions of individual molecules but with the
time-averaged force  on a given  area that can be measured  by a pressure gage.

 

From the macroscopic point of view, we are always  concerned with volumes that are very  large compared to molecular dimensions, and
therefore a system (to be defined next) contains many molecules, and this is
called continuum. The concept of continuum loses validity when the mean free path of molecules
approaches the order of typical
system dimensions


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