( ( Mechanical waves ) ( ( ( transport energy ) ( through ( a medium ) ) ) . ) )
(ROOT (S (NP (JJ Mechanical) (NNS waves)) (VP (VB transport) (NP (NN energy)) (PP (IN through) (NP (DT a) (NN medium)))) (. .)))
Mechanical waves transport energy through a medium.
(ROOT (S (NP (NP (NNP Matter)) (SBAR (IN that) (S (NP (JJ mechanical) (NN wave) (NN energy)) (VP (MD can) (ADVP (RB only)) (VP (VB travel) (PRT (RP through))))))) (VP (VBZ is) (ADJP (JJ medium))) (. .)))
Matter that mechanical wave energy can only travel through is medium.