( ( ( Mechanical ( waves ( transfer energy ) ) ) ( through matter ) ) ( ( called ( the medium ) ) . ) )
(ROOT (S (NP (NP (JJ Mechanical) (NNS waves) (NN transfer) (NN energy)) (PP (IN through) (NP (NN matter)))) (VP (VBD called) (NP (DT the) (NN medium))) (. .)))
Mechanical waves transfer energy through matter called the 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.