The classical Mechanics was developed on the basis of Newtons three laws they are (i) law of inertia, (ii) law of force and (iii) law of action and reaction. These laws include the concept of absolute mass, absolute space and absolute time. The classical mechanics explains correctly the motion of celestial bodies like planets, stars and macroscopic as well as microscopic terrestrial bodies moving with non-relativistic speeds (v << c, where c being the velocity of light in vacuum). The inadequacies of classical mechanics are as follows: 

(i) It does not hold in the atomic dimension i.e. it can not explain the non-relativistic motion of atoms, electrons, protons etc.

(ii) It could not explain the stability of atoms.

(iii) It could not explain the observed spectrum of black body radiations.

(iv) It could not explain the observed variation of specific heat capacities of metals and gases.

(v) It could not explain the origin of discrete spectra of atoms since according to classical mechanics the energy changes are always continuous. 

(vi) It could not explain large number of observed phenomena like photoelectric effect, compton effect, Raman effect etc. 

These inadequacies of classical mechanics led to the development of Quantum Mechanics.