Molecular, atomic structure and energy transfer

Gases : ‘simple’ collisions do the job. (With the help of statistics.)
But – “macroscopic parameters” (description) needed ... and possible.

A very useful concept : ideal gas

Solids : a lot more complicated.   Actual arrangement of molecules varies.
( Gives rise to all kinds of phenomena )   Still, mechanical models are extremely useful.

Note : “models” – all over the place.

Average kinetic energies of constituents : a full description of everyday phenomena.
This is one of the big triumphs of classical physics.

But ... what about light ?