( ( ( ( ( Classical Mechanics ) , ) ( ( the behavior ) ( of ( objects ( of ( macroscopic size ) ) ) ) ) ) , ) ( ( can ( be ( ( ( explained ( as ( ( a ( special case ) ) ( of ( Quantum Mechanics ) ) ) ) ) , ) ( although ( ( in practice ) ( ( Classical Mechanics ) ( was ( understood first ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Classical) (NNP Mechanics)) (, ,) (NP (NP (DT the) (NN behavior)) (PP (IN of) (NP (NP (NNS objects)) (PP (IN of) (NP (JJ macroscopic) (NN size)))))) (, ,)) (VP (MD can) (VP (VB be) (VP (VBN explained) (PP (IN as) (NP (NP (DT a) (JJ special) (NN case)) (PP (IN of) (NP (NNP Quantum) (NNPS Mechanics))))) (, ,) (SBAR (IN although) (S (PP (IN in) (NP (NN practice))) (NP (NNP Classical) (NNP Mechanics)) (VP (VBD was) (VP (VBN understood) (ADVP (RB first))))))))) (. .)))
Classical Mechanics, the behavior of objects of macroscopic size, can be explained as a special case of Quantum  Mechanics, although in practice Classical Mechanics was understood first.
(ROOT (S (NP (NP (DT The) (JJ specialized) (NN study)) (PP (IN of) (NP (NP (DT the) (NN motion)) (PP (IN of) (NP (NP (NNS objects)) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (ADJP (JJ atomic/subatomic) (PP (IN in) (NP (NN size)))))))))))) (VP (VBZ is) (VP (VBN called) (NP (NN quantum) (NNS mechanics)))) (. .)))
The specialized study of the motion of objects that are atomic/subatomic in size is called quantum mechanics.